Male Mating Strategies within a Shifting

Competitive Landscape: Performance and

Phenotypic Correlates of Mate Guarding

Success

by

Megan McPhee

A thesis submitted in conformity with the requirements

for the degree of Master of Science

Ecology and Evolutionary Biology

© Copyright by Megan McPhee 2015

ii

MALE MATING STRATEGIES WITHIN A SHIFTING COMPETITIVE

LANDSCAPE: PERFORMANCE AND PHENOTYPIC CORRELATES OF

MATE GUARDING SUCCESS

Master of Science

2015

Megan McPhee

Ecology and Evolutionary Biology

University of Toronto Scarborough

Mate-guarding males who limit access of rivals to females may be likewise preferred by

females, or their mating advantage may lie only in excluding opponents. In the jumping spider

Phidippus clarus, males guard immature females, mating once females synchronously moult. To

investigate factors contributing to mate guarding success in the field, we compared the

morphology, competitive and courtship success of guarding and non-guarding males collected

throughout their season. Guarders were larger than roamers only during the time when females

moult, and also demonstrated both higher fighting and courtship success independent of size-

related advantages. Thus, high levels of male-male competition during female moult implicates

male-male contests in determining mate-guarding success. Given the proposed significance of

mate guarding to male fitness, heritability of traits related to competitive ability and guarding

may explain the observed correspondence between sexual selection via female choice and male-

male competition.

iii

ACKNOWLEDGMENTS I would like to express extreme gratitude to my co-supervisors, Prof. Maydianne C.B.

Andrade and Prof. Andrew C. Mason, for helping me to follow a dream since childhood and a

passion since adulthood, while providing both the support and freedom in which to do so. Their

direction, expertise and passion for the scientific method were indeed invaluable to me.

I would also like to thank my committee members Prof. Darryl T. Gwynne and Dr.

Kenneth Welch for their input and direction, as well as my funding source NSERC for the

CGSM Scholarship they bestowed upon me. I greatly appreciation the advice and support of all

members of the Andrade and Mason lab, as well as to the students, faculty and staff at UTSC. A

special thanks is owed to Terrence Chang for his ceaseless enthusiasm for our topics of research

and to my parents who were the first to support my scientific endeavors, both intellectually and

financially.

iv

TABLE OF CONTENTS

ACKNOWLEDGMENTS ............................................................................................................................... v

List of Figures ........................................................................................................................................... vi

List of Tables ............................................................................................................................................ vi

Abstract ......................................................................................................................................................... ii

Chapter One: General Introduction ............................................................................................................... 1

Chapter two: Male mating strategies in response to a shifting competitive landscape: A field study .......... 8

Introduction ............................................................................................................................................... 8

Methods .................................................................................................................................................. 14

Research Sites ..................................................................................................................................... 14

Surveying and Collection .................................................................................................................... 14

Morphological Measurements ............................................................................................................. 17

Statistical Analyses ............................................................................................................................. 17

Results ..................................................................................................................................................... 20

Population Structure ............................................................................................................................ 20

Male Size and Guarding Success across the Reproductive Season .................................................... 24

Discussion ............................................................................................................................................... 29

Chapter Three: Male courtship and fighting performance as a function of guarding status ....................... 38

Introduction ............................................................................................................................................. 38

Methods .................................................................................................................................................. 43

P. clarus reproductive behaviour ........................................................................................................ 43

Collection and Housing ....................................................................................................................... 44

Signal Recording ................................................................................................................................. 45

Courtship Trials .................................................................................................................................. 45

Competition Trials .............................................................................................................................. 46

Signal Analysis ................................................................................................................................... 48

Statistical Analyses ............................................................................................................................. 49

Courtship Outcome and Signal Characteristics Related to Status ....................................................... 50

Contest Outcome and Male Characteristics Related to Status ............................................................ 50

Results ..................................................................................................................................................... 51

Courtship Trials and Signal Characteristics Related to Male Status ................................................... 51

Contest Outcome and Signal Characteristics Related to Male Status ................................................. 56

Focal-Male Model: .............................................................................................................................. 60

Discussion ............................................................................................................................................... 63

v

Guarding Male Courtship Success ...................................................................................................... 63

Guarding Male Contest Success ......................................................................................................... 65

Chapter 4: General Conclusion ................................................................................................................... 70

References .................................................................................................................................................. 72

vi

List of Figures Fig. 1. 1. Male Phidippus clarus ................................................................................................................... 9

Fig. 1. 2. Female Phidippus clarus ............................................................................................................... 9

Fig. 2. 1. Field Site Map ............................................................................................................................. 23

Fig. 2. 2. Number and status of males and females collected across the season ......................................... 27

Fig. 2. 3. Proportion of collected males found guarding or roaming across the season .............................. 28

Fig. 2. 4. Male status as a logistic function of body size ............................................................................ 31

Fig. 2. 5. Average body size of guarders and roamers across the season ................................................... 33

Fig. 3. 1. Courtship success as a logistic function of vibration rate for guarders and roamers ................... 59

Fig. 3. 2. Relationship between male body size and courtship vibration rate ............................................. 60

Fig. 3. 3. Contest success for guarders as a logistic function of vibration rate ........................................... 64

Fig. 3. 4. Relationship between body size and aggressive vibration rate .................................................... 67

List of Tables Table 2. 1 PC1 Factor Loadings.................................................................................................................. 24

Table 2. 2. Analysis of predictors of field status ........................................................................................ 30

Table 3. 1. Analysis of courtship outcomes ................................................................................................ 58

Table 3. 2. Both-male analysis of contest outcomes: Relative ................................................................... 62

Table 3. 3. Both-male analysis of contest outcomes: Relative ................................................................... 63

Table 3. 4. Focal-male analysis of contest outcomes: Absolute ................................................................. 66

Table 3. 5. Focal-male analysis of contest outcomes: Relative .................................................................. 66

1

CHAPTER ONE: GENERAL INTRODUCTION

As first acknowledged by Darwin (1859, 1871), sexual selection can shape the evolution

of male and female traits through the effects of two mechanisms; male-male competition and

female mate choice. Empirical and theoretical research on sexual selection since then has tended

to study these processes independently, emphasizing the role of one or the other in the evolution

of traits (Hunt, Breuker, Sadowski, & Moore, 2009). However, male-male competition and

female mate choice rarely occur in isolation (Wong & Candolin, 2005), and their interaction will

influence the outcome of these processes in nature, and thus their evolutionary consequences.

The net effect of competition and choice will partly depend on whether these processes occur

simultaneously or sequentially, and whether the traits that confer success in each process are

convergent or divergent.

In many species, males attempt to limit access of rival males to females (competition) by

guarding. In these cases, competition and choice may occur sequentially, and this temporal

separation between fighting and mating attempts can provide an ideal opportunity to study the

roles of male-male competition and mate-choice on the evolution of mating strategies. Although

mate guarding is common across the animal kingdom (Andersson, 1982) and has been the focus

of various theoretical and empirical studies (e.g. Grafen & Ridley, 1983; Härdling, Kokko, &

Elwood, 2004; Komdeur, 2001; Mathews, 2003), the relative importance of the interaction

between choice and competition in the evolution of guarding has remained a topic of debate

(Estrada, Yildizhan, Schulz, & Gilbert, 2010).

In this thesis, I seek to understand the ecological and physiological factors involved in sexual

selection and how these affect the evolution of guarding strategies of males. To do this, I use a

2

combination of field and laboratory studies to test hypotheses about mate-guarding in the

jumping spider Phidippus clarus (Araneae: Salticidae). P. clarus shows pre-copulatory mate

guarding during a temporally restricted reproductive season (June, July and August) with

relatively synchronous female maturation (Hoefler & Jakob, 2006). This species is found in old

field habitats across temperate North America where it makes use of the upper portions of woody

or herbaceous plants for retreats and nests (Hill, 2014). In June, roaming adult males seek out

and cohabit with immature (final instar) females which nest within silken retreats constructed in

rolled leaves (Hoefler & Jakob, 2006). During their final instar, females build a thick silk

envelope inside the retreat, and apparently do not leave until they moult (pers obs).

Protandry results in a male-biased operational sex ratio during this period of the mating

season, when males compete for opportunities to guard. Males prefer larger females and large

males have an advantage in competition, so the outcome is that males and females pair

assortatively by size (Hoefler 2007). Following a synchronous female moult period (~3 days,

Hoefler & Jakob, 2006) the operational sex ratio shifts to even, and guarding males attempt to

mate with newly-matured females. Guarding males are found on or near the nest, in close

proximity to females. Near the moulting period, males move inside the silk retreat and court

females. After moulting and mating, adult females spend time foraging outside of their nest

during the day (Hoefler & Jakob, 2006; pers obs). It has been suggested that during this period,

guarding no longer occurs, and male mating success will depend on encountering and persuading

previously-mated females to copulate (female receptivity decreases after guarding and mating,

Elias et al 2014; Sivalinghem et al., 2010, Elias et al 2011). Laboratory studies have shown

mature females are capable of mating multiply, however it is unclear how often this occurs in

nature. Although there have been no sperm competition studies in jumping spiders (Schneider &

3

Andrade 2011), first male sperm precedence is the most likely outcome of polyandry since the

morphology of their genitalia is such that the first sperm to enter would be the first to exit at

fertiliization (Elgar 1998). Moreover, first-male sperm precedence is expected to impose strong

selection for protandry and pre-copulatory mate guarding, as seen in P. clarus.

P. clarus males produce variable multi-modal signals (visual and vibrational) that are

important in competition and courtship. As is characteristic of all jumping spiders, P. clarus

possesses a remarkable visual acuity that is important in both prey capture (Li, Jackson, & Lim,

2003) and reproduction (Clark & Morjan, 2001) and males have striking, sexually dimorphic

visual ornaments which are utilized in complex courtship displays and during inter-male

competition (Fig. 1.1, 1.2; Crane, 1949; Jackson, 1982). In P. clarus, in addition to the bright red

colouration of the abdomen, males have enlarged, black forelegs ornamented with black tufts in

contrast to the more cryptic brown and orange females (Figure 1). The forelegs are outstretched

during ritualized competition between males, and are an indicator of size, but they may also be

used directly for grappling when contests escalate to physical combat (Elias et al., 2008). In

addition to visual displays, like some other recently studied salticids, P. clarus males produce

several different types of vibratory signals in both inter- and intra-sexual contexts. Thus, when

guarding males are challenged by rivals, the competitors engage in aggressive, stereotyped visual

and vibratory signalling (Elias et al., 2008; Kasumovic, Elias, Sivalinghem, Mason, & Andrade,

2010). The vibratory signals directed at competitors compared are distinct from those directed at

adult females during courtship and signal features are correlated with success in mating and in

inter-male competition (Elias, Kasumovic, Punzalan, Andrade, & Mason, 2008; Elias,

Sivalinghem, Mason, Andrade, & Kasumovic, 2010; Sivalinghem, Kasumovic, Mason, Andrade,

& Elias, 2010). Guarding males perform intricate courtship displays involving both visual and

4

vibratory signals prior to copulation (Sivalinghem et al., 2010). In addition, recent work shows

that males also direct vibratory signals to immature females during guarding, and these may

affect female receptivity later (Elias, Sivalinghem, Mason, Andrade, & Kasumovic, 2014).

Fig. 1. 1. Male Phidippus clarus. The male is marked (blue paint on abdomen) for individual

identification (see Chapter 3). Image courtesy of Ken Jones.

Fig. 1. 2. Female Phidippus clarus. Image courtesy of Ken Jones.

5

The seasonal shifts in the importance of male-male competition and female choice that occur

across the breeding season make P. clarus an ideal system to investigate how mate-guarding may

translate to mating success for males within a variable environment. Here I assess phenotypic

correlates of performance and fitness in males as a function of their status in the field (successful

guarder or not), and examine how this is reflected in the characteristics of signals and signalling

behaviour, particularly as the competitive environment and sex ratio shift during the mating

season.

In Chapter two, I report the results of a field survey on a natural population of P. clarus

across the mating season. I used collection data to document the phenology and occurrence of

mate guarding, and compare the phenotype of successful guarders to males that are not guarding

(roamers). Larger males are more likely to win fights (Elias et al., 2008; Hoefler, 2007;

Kasumovic, Elias, Punzalan, Mason, & Andrade, 2009; Kasumovic, Mason, Andrade, & Elias,

2011), but the relative size of guarders and roamers may change over time because (1) larger

males commence guarding when females are most reproductively valuable (i.e., near the

female’s moult date, the takeover hypothesis) or (2) successive fights act as a progressively more

restrictive filter on male traits as the female moult date approaches and male motivation to fight

increases (the fight effort hypothesis). I tested a common prediction of both of these

hypotheses—that the most extreme difference in the phenotypic traits of guarders and roamers

would occur near the time of the female’s moult date, when females are most reproductively

valuable to males. While previous work documented the competitive advantage of larger males

(Elias et al., 2008; Hoefler, 2007; Kasumovic, Elias, Punzalan, Mason, & Andrade, 2009;

Kasumovic, Mason, Andrade, & Elias, 2011), it is not clear whether this translates into guarders

being larger than roamers in nature. This is an important point because it has also been shown

6

that competition in P. clarus is mediated by advantages of residents (i.e., males that are already

guarding) over intruders (i.e., roamers) and by a ‘winner’ effect whereby males that have won

previous competitions are more likely to win again compared to males that had previously lost

(Kasumovic et al., 2009, 2010, 2011). Thus it is unclear how to extrapolate from staged

laboratory contexts to field dynamics.

In Chapter Three, I tested whether males differed in their competitive ability or courtship

success as a function of their status as ‘guarders’ or ‘roamers’. In this chapter, I staged

competitive contests between males collected as roamers and guarders in the field. I tested

whether factors other than the relative size of males in these roles (quantified in Chapter Two)

determined guarding status and fight performance (Elias et al., 2008; Hoefler, 2007; Kasumovic

et al., 2009, 2011). I was particularly interested in the effect of variation in behavioural and

aggressive signalling traits of guarders compared to roamers. In this chapter, I also tested

whether courtship success was predicted by the same traits as competitive success. I paired

individual males with unmated females and compared courtship performance and intersexual

signals of guarders and roamers. While previous laboratory work has identified male traits

important in male-male competition and female mate choice respectively, empirical evidence on

how these traits are related to mate-guarding success in nature is lacking.

By assessing seasonal variation in male traits involved in successful mate-guarding and

identifying how these and other traits are related to competitive success and female preferences, I

aim to link the current body of lab-based research in P. clarus to natural phenology and

population dynamics. Features of the mating system and natural history of this species suggest it

could be an ideal model for examining evolutionary consequences of interactions between the

7

multiple mechanisms of sexual selection, particularly as they are linked to variation in the

environment.

8

CHAPTER TWO: MALE MATING STRATEGIES IN RESPONSE TO A

SHIFTING COMPETITIVE LANDSCAPE: A FIELD STUDY

Introduction

Mate-guarding is expected to evolve as a male mating strategy when the paternity

benefits outweigh the time and energy costs associated with guarding (Bel-Venner & Venner,

2006; Komdeur, 2001). Costs include forgoing other possible mating opportunities (Birkhead &

Møller, 1992; G. A. Parker, 1974), restricted feeding during guarding (Alberts, Altmann, &

Wilson, 1996; Girard-Buttoz et al., 2014; Komdeur, 2001; Prenter, Elwood, & Taylor, 2006;

Sparkes, Keogh, & Pary, 1996), energetic or injury costs of agonistic interactions with rival

males (Galimberti, Sanvito, Braschi, & Boitani, 2007; Plaistow, Bollache, & Cezilly, 2003),

higher predation risks (Cooper, 1999; Fahey & Elgar, 1997), and any additional energy

requirements of maintaining close proximity to females (Adams & Greenwood, 1983; Wilcox,

1984) including mate-guarding courtship (Elias et al., 2014). Despite the costs, mate guarding

has evolved in many different taxa where it may manifest as (pre-copulatory) guarding of

subadult or adult potential mates or as post-copulatory guarding of mates; with both forms of

guarding being important in terms of sexual selection on males (Danielsson, 2001; Ward, 1988).

Pre-copulatory guarding entails the additional risk that a guarding male may invest significant

energy and time, and yet end up losing out completely on any reproductive benefits if evicted by

a rival (Bel-Venner & Venner, 2006) or rejected by the female he is guarding (Chuang-Dobbs,

Webster, & Holmes, 2001; Elias et al., 2014; Huffard, Caldwell, & Boneka, 2010; G. A. Parker,

1974; Watson, 1990).

The type of mate-guarding to occur depends primarily on species-specific life history

traits and population dynamics related to reproduction. Post-copulatory guarding of females

9

(after insemination is secured), is predicted in species with longer windows of receptivity or

fertility (Harts & Kokko, 2013), and/or last-male sperm precedence (Holdsworth & Morse,

2000). On the other hand, pre-copulatory guarding typically occurs when acquiring the first

mating with a female has crucial fitness benefits for a male due to restricted periods of

receptivity and/or first male sperm precedence. This form of mate guarding is more likely to

evolve when males can predict female receptivity and when monopolization of females prior to

this time is feasible (Austad, 1982; Clutton-Brock, 1989; G. A. Parker, 1974; Yamamura, 1987).

Despite the additional risk inherent in pre-copulatory mate-guarding, this alternate guarding

tactic has been documented in a wide range of taxa, including mammals (Schubert, Schradin,

Rödel, Pillay, & Ribble, 2009), fish (Morbey, 2002), frogs (Yamamura, 1987), crustaceans

(Bauer & Abdalla, 2001; Cornet, Luquet, & Bollache, 2012; Härdling et al., 2004; Jormalainen,

1998; Plaistow et al., 2003; Wada, Tanaka, & Goshima, 1999), insects (Arakaki et al., 2004;

Estrada et al., 2010), and spiders (Bel-Venner & Venner, 2006; Bridge, Elwood, & Dick, 2000;

Holdsworth & Morse, 2000; Robert R. Jackson, 1986).

Here, I focus on pre-copulatory mate guarding, which is particularly interesting when

males guard immature females. In this case, the maximum possible reproductive gains of

guarding remain constant while the risk of losing those benefits decreases continuously as

females approach sexual maturity, since the time in which take-overs can occur and the energetic

expenditure needed to survive until female maturation decrease with time. Thus it is predicted

that mate guarding should become increasingly profitable as the window of female

receptivity/maturity approaches (Elwood & Dick, 1990; Grafen & Ridley, 1983; G. A. Parker,

1974; Watson, 1990). Results from previous arthropod studies have been consistent with this

prediction, demonstrating that guarding often occurs close to the onset of female sexual

10

receptivity (Cornet et al., 2012; Mathews, 2003), when the time left prior to maturation and

likelihood of a take-over before mating is at its lowest.

The time during a female’s cycle when guarding would be adaptive for a given male will

depend, however, on each male’s competitive ability as this will impact the likelihood of a take-

over, and thus the risks associated with mate guarding (Grafen & Ridley, 1983; Härdling et al.,

2004; G. A. Parker, 1974). Male phenotype (including size) may also affect the likelihood that

the female will accept the male once she is receptive and thus the likelihood of a payoff from

guarding effort (Iyengar & Starks, 2008). Therefore for a searching male that encounters an

immature female, the decision of whether or not to guard will depend on the female’s status

(alone or guarded), developmental stage (likely time to maturity), the likelihood that the female

will accept the male as a mate, and the likelihood that the male could defend against rivals until

she matures within the current competitive environment (Bel-Venner & Venner, 2006; G. A.

Parker, 1974). Male competitive ability, and thus the likelihood of successful guarding, will

often vary with male phenotype and resource holding potential (the capacity of an animal to

defend a resource through an escalated fight against an opponent, RHP; Alonso-Alvarez,

Doutrelant, & Sorci, 2004; Caldwell & Dingle, 1979; Hack, Thompson, & Fernandes, 1997;

Parker, 1974; Simmons, 1986). Among the traits related to competitive ability, male size is

commonly favoured by precopulatory sexual selection (mediated by both competition and

choice; Andersson, 1994; Bonduriansky & Rowe, 2003; Dodson & Schwaab, 2001). A size-

advantage may be especially likely in systems where males compete directly for access to

immature females (Grafen & Ridley, 1983), and several studies have shown that larger males are

at an advantage in obtaining guarding positions (Berrill & Arsenault, 1984; Donaldson &

Adams, 1989; Elgar, De Crespigny, & Ramamurthy, 2003; Johnsen, Lifjeld, & Krokene, 2003;

11

Poirier, Whittingham, & Dunn, 2004) and more specifically in both making takeovers and

resisting such attempts by rival males (Bel-Venner & Venner, 2006; Ward, 1983).

Decisions about when to guard and how much energy to invest in guarding have been the

subject of considerable theoretical work. The takeover hypothesis, first modeled by Grafen &

Ridley (1983) frames mate-guarding as a male decision-making problem, and predicts that when

1) males compete directly for females, 2) guarding is costly to males, and 3) takeovers are

frequent, a size-advantage will allow larger males to start guarding later, when females are closer

to their moult dates. . This and related models were developed with reference to the mate-

guarding crustacean Gammarus pulex where empirical work shows males prefer females closest

to moult (Birkhead & Clarkson, 1980). Despite strong evidence for large male advantages in

male-male competition and size-assortative pairing close to female moult (Cornet et al., 2012;

Jormalainen, 1998; Plaistow et al., 2003), other studies show thatG. pulex males tend to start

guarding females earlier than smaller males (Cornet et al., 2012; Elwood & Dick, 1990; Ward,

1983). The failure to support ‘takeover’ predictions in this species has been attributed to the

relative rarity of takeovers and the low cost of guarding for large males (Elwood & Dick, 1990).

However, empirical evidence in support of the ‘takeover’ hypothesis has been found in the orb-

weaving spider Zygiella x-notata, where experimental studies have shown that 1) direct male-

male competition drives positive selection on guarding male size and, 2) that larger males opt to

guard females closer to their moult date than smaller males (Bel-Venner & Venner, 2006).

However, temporal changes in male phenotypic traits related to mate guarding success

may also be influenced by the outcome of continuous intrasexual competition. The ‘fight effort’

hypothesis proposes that increased male fighting effort for guarding positions is expected as

females approach moult and their reproductive value increases. When all males are highly

12

motivated to fight for high-value females, larger males will usually win. Consistent with this

idea, theory predicts increasingly intense and frequent male-male contests as the female’s moult

approaches (Elwood & Dick, 1990; Härdling et al., 2004). These two hypotheses operate via

different mechanisms (male choice versus direct intrasexual competition) yet both may operate

simultaneously. Despite empirical and theoretical evidence for both the takeover hypothesis and

the fight effort hypothesis, tests of the predicted temporal patterns in male traits influencing

guarding success in nature remain rare.

Here I studied seasonal variation in the phenotype of successful mate-guarding males in a

field population of Phidippus clarus. P. clarus is protrandrous and shows pre-copulatory mate

guarding during a 3-month reproductive season with relatively synchronous female maturation

(Hoefler & Jakob, 2006, Chapter one). These features make P. clarus an ideal taxon to

investigate the temporal predictions of the takeover and fight effort hypotheses. In June, roaming

adult males seek out and cohabit with subadult (final instar) females which nest within silken

retreats constructed in rolled leaves (Hoefler & Jakob, 2006). During cohabitation, males attempt

to repel potential rivals. Lab-based contests suggest males will have higher success if they are

relatively large and heavy (Elias, Sivalinghem, et al., 2010; Hoefler, 2007), and if they locate

females before rivals due to resident and winner effects (Kasumovic et al., 2009, 2011). The

advantage of larger males in contests in combination with a demonstrated male preference for

larger, more fecund females has been implicated in size-assortative cohabitation pairings

observed near female moult-dates in the field (Hoefler, 2007).

Independent of seasonal variation in the benefits of guarding, the intensity of male-male

competition may also change over the course of the breeding season since the sex ratio shifts

from male-biased to even after females moult (Elias, Andrade, & Kasumovic, 2011; Hoefler,

13

2007, 2008; Kasumovic et al., 2010). Since adult females spend time foraging during the day

after moulting (Hoefler & Jakob, 2006; per obs), it has been suggested that male mating success

following the females’ moult may be most strongly dependent on female choice-driven courtship

success (Elias, Sivalinghem, et al., 2010; Sivalinghem et al., 2010). A second goal of this study

was to assess temporal patterns in female occupation of retreats through the season, particularly

with respect to the pre-moult, compared to post-moult, period.

To date, no study has assessed whether male body size underlies cohabitation success in

nature in P. clarus. Furthermore, it is unknown whether there are temporal patterns in the relative

size of guarding males across the season matching those which would be predicted by the

takeover and fight effort hypotheses in this species. Consequently, the objective of this study was

to determine phenotypic correlates of male mate guarding success in P. clarus to test common

predictions of these two hypotheses. I performed a field survey and collection experiment on a

natural population of P. clarus, recording the occurrences of guarding and collecting both

guarding and roaming males throughout the breeding season and assessing size differences

between the two groups. I predicted that males found guarding would be on average larger than

males found roaming, and that this disparity would be greatest immediately preceding and during

the period of synchronous female moult, when the expected male fitness value of cohabitation is

highest. This study would be one of the few tests of predictions made by both the takeover and

fight effort hypotheses in nature, and provide insight into the selective processes involved in the

evolution of male mating tactics within the context of shifting population dynamics.

14

Methods

Research Sites

All field work was conducted throughout the summer months of 2014 in four old fields

(Fig. 2.1) dominated by a variety of grasses and common milkweed (Asclepias syriaca) within

the University of Toronto’s Koeffler Scientific Reserve in Joker’s Hill, King City, ON, Canada

(44° 03’ N, 79° 29’ W). Fields ranged in size from 16 x 50 to 48 x 43 m (Fig. 2.1) and were 10 -

150 m apart. Males were collected from fields 2, 3, and 4 only (Fig. 2.1). Field 1 was susceptible

to flooding and not suitable for regular collection of males, so this field was used exclusively to

collect females for behavioural experiments (Chapter two). The distance between the fields and

(in the case of field 4) borders of dispersion-limiting habitat (forest and a stream) is likely to

have reduced movement of males from one field to the other. However, it is unlikely that overall

population size was significantly affected through my continuous sampling of males within each

field as every collection field was contiguous with other old fields containing similar vegetation,

in which P. clarus have been observed (MCBA pers comm) which could thus serve as a source

for additional males (and see Results).

Surveying and Collection

Artificial retreat tubes (retreats) were constructed using 1.9 cm diameter rubber tubes cut

to be 3.8 cm long and attached at one end of 1.5 m bamboo poles (Backyard X-Scapes).

Artificial retreats were used in order to be able to consistently locate cohabiting pairs since

previous research has demonstrated that P. clarus readily creates retreats within tubing (Hoefler

& Jakob, 2006). The translucent tubing used in this study was covered in opaque duct tape to

make retreats more attractive to retreating females. Before the start of the growing season (April

27, 2015), poles were inserted into the ground at each field in approximately 3 x 3 m grids so

15

that retreats were ~1 m above ground. All retreats were marked with labelled flagging tape for

identification.

Of the four field sites, a field was designated for the collection of virgin females early in

the season for future use in mating and competition trials (field 1=66 retreats, Chapter two),

whereas the remaining three were designated for collection of guarding and roaming adult males

(field 2, n =100 retreats; field 3 n =80; field 4 n=80).

Retreats were surveyed on a bi-weekly basis for P. clarus emergence and retreat

colonization, starting on May 17, 2014. The first immature individuals (females and males were

indistinguishable by eye) were found on June 5, 2014. Following this date, retreats were checked

for occupancy 2 – 3 times a week between 1000 and 1400 hours, and the presence of either

immature females or males occupying marked retreats was recorded. After the first observation

of a cohabiting pair (June 23, 2015), we commenced collections. During each collection day, we

collected all males found cohabiting with immature females in retreats, collected any males

found roaming away from retreats on the same day, and noted the presence and development

stage of any females found in retreats. For all males, the date, status (roaming or guarding), field

location, and associated retreats (for guarders) were recorded. Mature males are readily

recognized given their distinct colouration, foreleg ornaments, and enlarged pedipalps (Hill,

2014). Females that were being guarded by collected males were left in retreats to maximize the

opportunity for male competitive processes to take place between collection days. The

developmental stage (immature or adult) of females was determined based on morphology,

colouration, and size (Hill, 2014). Once collected, all spiders were transported back to the lab for

morphological measuring. We ceased surveys on July 19th 2015 when all females were sexually

16

mature and many had produced egg sacs, and males were no longer being found regularly in the

field (males are relatively short-lived).

Our collection inevitably altered the number of males in our focal fields on our collection

days. Given that P. clarus is common and found throughout the 350 ha field station, it is unlikely

that collection would deplete the local population. We would expect dispersal of males into

fields continuously during this period. If dispersal was not sufficient to counteract the effects of

collection however, given that we did not collect females, our methods would have led to a

progressive shift in the sex ratio such that it would become more female-biased than an

undisturbed population as the mating season progressed. Since lower densities of males would

lead to a decrease in competition-based sexual selection on males over time (Andersson & Iwasa,

1996), it would tend to make it less likely that our predictions from the takeover and fight effort

hypotheses would be supported. Our test of these hypotheses is thus conservative given our

methods.

It is also possible that collecting males would lead to a depletion of males of a particular

size class as the season progressed. For example, this might occur if males mature over weeks

and first-maturing males are either larger (e.g. Neumann & Schneider, 2015; Schneider, 1997) or

smaller than males that mature later (e.g. Uhl, Schmitt, Schäfer, & Blanckenhorn, 2004). This is

not likely to affect our test of the takeover hypothesis since we are comparing guarders and

roamers collected in the same time interval. We nevertheless use our data to test for such an

effect by examining the average size and numbers of males (both guarders and roamers) as a

function of collection date.

17

Morphological Measurements

Spiders were maintained on regular feeding and watering schedules (see Chapter two for

details) until they died, at which time they were preserved in 70% ethanol. After their death, all

males were dissected and digitally photographed (Nikon Digital Camera DXM 1200) using a

Zeiss microscope (Stemi 2000C) and NIS-Elements imaging software (v. 4.0, Nikon). Once

captured, photographs were measured to scale using ImageJ software (Schneider, Rasband, &

Eliceiri, 2012). We measured various aspects of body size, including cephalothorax dimensions

(width and length), the length of the different segments of the leg, as well as the distance

between the two front legs at the coxa on the ventral surface (Table 1). We also measured the

width of the tibial brush, which is a foreleg ornament that may be important in inter-male

signaling of size. We were unable to take measurements of body mass, as survey of all fields and

collection of males was time and labour-intensive, and the large number of individuals collected

made timely weighing unfeasible. However, male size and mass were significantly correlated in

other studies (Sivalinghem et al., 2010).

Statistical Analyses

We used a principle components analysis to reduce potentially correlated morphological

variables into fewer metrics of male body size (Table 1). The first principle component (PC1 –

‘body size’) explained 83.8% of the phenotypic variation seen within the dataset, and had

positive loadings for all measurements, with the heaviest loading on femur, tibia and metatarsus

length, tibial brush and cephalothorax dimensions. As all other components represented an

equally small quantity of phenotypic variation relative to the first (< 10%). Factor scores from

PC1 were used as the single body size index in all further analyses.

18

Fig. 2. 1 Google earth image of the region of the University of Toronto’s Koeffler Scientific

Reserve at Joker’s Hill (King City, ON, Canada, 44° 03’ N, 79° 29’ W) where the study was

conducted. Artificial retreats were placed in each of the 4 outlined fields in a grid to facilitate

regular surveys and collections. Females were collected from retreats in field 1 for studies

described in Chapter two and guarding and roaming males were collected from fields 2-4.

19

Table 2.1. Factor loadings for the first principle component of morphological variables measured

on Phidippus clarus males collected from a field population throughout the breeding season. All

variables loaded most heavily and relatively equally on PC1, thus supporting the use of PC1 as

the single male-size-related phenotypic variable.

PC1

Cephalothorax Width 0.391

Cephalothorax Length 0.343

Coxa length 0.146

Trochanter length 0.116

Femur 0.434

Patella 0.271

Tibia 0.437

Metatarsus 0.314

Tarsus 0.125

Ventral Coxal Gap 0.119

Tibial Brush 0.336

20

To determine whether male body size predicted guarding success, I used backwards

stepwise logistic regression models with male’s collection status (guarding or roaming) as the

categorical response variable. The model included collection field, body size, and collection date

index as predictors. Collection dates were pooled into early-, mid-, and late-season based on our

observed timings of male and female maturation. Early-season (June 23rd – June 29th) was

categorized as the time from first observation of mature males in the field to the date just prior to

the first observation of a mature female. Mid-season (June 30th – July 8th) encompassed the

period of female moulting (from 0 to 100% of observed females mature), and late-season (July

10th – July 18th) was categorized as all collection dates after all females were mature.

Finally, to determine whether there were overall changes in the body size of males

collected as the season progressed a generalized linear mixed model with a gamma error

distribution was used with collection date index as a fixed effect and collection field as a random

factor. Post hoc Tukey’s tests were performed to isolate the cause of any resulting significant

differences in male size across the different periods of the season.

All statistical analyses were performed using R (R Core Team, 2014) or SPSS (v. 23).

Results

Population Structure

Females

While the average occupancy of artificial retreats across the season ranged between 9%

and 21.5% in different fields, occupancy reached 70% on some days, indicating that the artificial

retreats could be readily located and provided suitable retreats for females and males. The

earliest mature cohabiting female was identified on June 30th, while the first mature female

observed roaming (not in a retreat) was found on July 2nd. By July 10th, all females found either

21

in retreats or roaming were mature (Fig. 2.2A). I observed a population-wide female moult

period of 10 days, which is consistent with results from other field studies on different wild

populations of P. clarus (Hoefler & Jakob, 2006).

Males

Confirming protandry in this species, 50% of males observed in the field were mature by

June 20th, 10 days prior to the first mature female appearing. The first instances of cohabitation

were recorded on June 23rd, when 100% of males observed in the population were mature (Fig

2.2B).

Anecdotally, we observed instances of an additional male found on the outside of retreat

tubes of cohabiting pairs, rapid guarder replacement after removal of original resident males, and

males engaging in physical combat next to a retreating female, which in some cases, resulted in

male mortality. Observed copulations only occurred within retreats between cohabiting pairs.

Mate guarding

Although not reported in previous studies, we also observed that mate guarding persisted

past the female moult period, with a relatively high number of males guarding retreating mature

females while other mature females were freely roaming and foraging (Fig 2.2B, Fig. 2.2). Males

were found copulating with females as late at July 16th, and females had laid and were guarding

egg sacs as early as July 14th. The number of cohabitating pairs peaked around June 30th,

coinciding with the start of the female moult period (Fig. 2.2). By July 19th, no cohabiting pairs

were found and roaming adult males were rare while we continued to find mature roaming

females until we ceased our surveys (July 23rd 2015).

22

Fig. 2. 2. Number of P. clarus females (A) and males (B) found in a field population throughout

the breeding season (2014) that were immature (grey) or mature (black) and were found either

inside or on a retreat (circles) or roaming on vegetation away from a retreat (diamonds).

23

Fig. 2. 3. Proportion of males collected guarding females (white bars) or roaming (black bars) at

three periods during the P. clarus breeding season, where females are immature in the Early-

season (June 23-29), are moulting or recently-moulted during the Mid-season (June30-July10)

and are all sexually mature during the Late-season (July 11-18). With approximately equal

sampling effort within each collection period, roaming males were more prevalent than guarding

males early-season than mid- and late-season, however this was not significant (χ2=3.6273, p=

0.1631, df=2). Cohabiting pairs were most prevalent during mid-season, when more than 60% of

males were guarding (also see Fig. 2.2), but guarding remained common through late-season.

Early- and mid-season males guarded immature females, whereas late-season males guarded

mature females.

n=24

n=99 n=88

n=38

n=92 n=82

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Early-season Mid-season Late-season

Pro

port

ion c

oll

ecte

d

Guarders

Roamers

24

Male Size and Guarding Success across the Reproductive Season

Logistic regression analysis using all collection data revealed that larger males were more

likely than smaller males to be found guarding females, however this effect was driven by

differences in the size of guarders and roamers during the peak season (mid-season x status,

β=0.383, p=0.0004; Fig. 2.4, Fig. 2.5, Table 2). Relative to early in the season, late-season males

were more likely to be guarders than roamers (β=0.736, p=0.037, Table 2). The best model for

these data (Table 2.2) also included male size independent of season and collection fields as

main effects, however neither of these variables was significant. A Hosmer-Lemeshow goodness

of fit test for the final model showed no evidence of poor fit (χ2=7.084, df = 8, p = 0.528).

25

Table 2. 2. Summary of final logistic regression model with variables predicting the status of

Phidippus clarus males (roaming or guarding) in a field population.

Variables in Full model Final Model1 variables with Post-hoc tests

Male Size Wald1 = 2.912, df = 1

β=-0.02, p=0.808

Time of Season Wald1 = 4.355, df = 2, p = 0.113

Early vs. Mid: β=0.574, p=0.101

Early vs. Late: β=0.736, p=0.037*

Collection Field Wald1 = 7.630, df = 3, p = 0.054

Field2= β=-0.595, p=0.278

Field3= β=0.166, p=0.745

Field4= β=0.289, p=0.583

Size x Season Wald1 = 13.197, df = 2, p = 0.001

Early vs. Mid= β=0.383, p=0.0004*

Early vs. Late= β=0.143, p=0.191 1Omnibus test of model coefficients, χ2 = 25.27, df = 8, p < 0.001 *Significant at an α=0.05 significance level

26

Fig. 2. 4. Male status (guarder vs. roamer) was a logistic function of male body size index (1st

principle component of body size measurements, Table 2.1). Larger males were more likely to be

guarding than small males (p<0.0001, n = 434).

27

I also tested whether the size of collected males (pooled across status) changed over the

season (Fig. 2.5, grey columns). It is clear that the size of males was related to the period when

they were collected overall (F2,420= 10.353, p< 0.001). However, while early-season males (n =

62) were smaller than males collected in the mid (n = 190, Tukey’s p < 0.001) or late season (n =

170, Tukey’s p < 0.001), there was no difference in the average size of males collected at mid

compared to late season (Tukey’s p = 0.994) despite the continued collection of many (mid: n =

99; late: n = 88) guarding males as the season progressed.

28

Fig. 2. 5. Average body size (PC1) of guarding (white bars), roaming (black bars) and pooled

(grey bars) males across the P. clarus breeding season. Males were significantly smaller early in

the season (Tukey’s, p < 0.05) and guarding males were significantly larger than their roaming

counterparts during mid-season (β = 0.383, df = 2, p = 0.0004). The average size of males did not

significantly change from mid- to late- season (Tukey’s, p > 0.05). Within early- and late-season,

guarding and roaming males where not significantly different in size from one another. (β =

0.143, df = 2, p = 0.191).

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

Early-season Mid-season Late-SeasonM

ale

Siz

e (P

C1)

29

Discussion Phidippus clarus has a relatively intense mating season with protandrous males guarding

immature females, all of which become mature within a 10 day period (Fig. 2.2). Thus the

expected payoff to males from guarding increases from early to mid-season. As predicted by

both the takeover and fight effort hypothesis, I found that guarder males in the field were

significantly larger in body size than their roaming counterparts, but only during mid-season,

immediately prior to and during female moult (Fig. 2.5), even though guarding was observed

throughout the mating season (Fig. 2.2, 2.5). During the early and late season, size differences

between roamers and guarders were not significant despite the large samples of collected males

(and thus, high power). This change in the characteristics of guarding males apparently occurs in

the context of a general seasonal shift in male size. I found evidence that early-season P. clarus

males were in general smaller than males found later in the season (Fig. 2.5). An average

increase in male size with the progression of the season is likely to be the consequence of a

trade-off between body size at maturation and developmental timing, where late-maturing, and

therefore larger males appear in the pool of available males later in the season (Prenter et al.,

2006; Schneider, 1997). This phenomenon however, cannot explain differences observed in male

size between guarding and roaming males at any given time in the season. Thus, it is likely that a

size disparity between guarders and roamers during female moult is the result of elevated sexual

selection on males as it relates to precopulatory mate-guarding.

Given the phenology of P. clarus (Hoefler & Jakob, 2006, Fig. 2.2), theory related to

male mating strategies (Elwood & Dick, 1990; Grafen & Ridley, 1983; Härdling et al., 2004)

predicts that mid-season would represent the period in which precopulatory guarding offers the

greatest benefit with the least cost. Guarding a female immediately prior to her final moult

minimizes opportunities for rival males to make take-overs before the female is receptive and

30

likewise requires the smallest investment in time and energy. Consequently, in conjunction with

synchronous female maturation, this dynamic should result in strong positive selection on traits

related to successful guarding around this period. Consistent with this, I observed direct male-

male contests, takeovers, and high male densities in the field. Studies on other species also

support this idea, as male-male competition has been implicated as the driving force for selection

on guarding males, favouring larger size in the period leading up to female receptivity in

Metellina segmentata (a species with an analogous mating systems to P. clarus; Prenter, Elwood,

& Montgomery, 2003). Field experiments on several orb-weaving spider species (M. mengeii

and Zigenilli x-notata) have confirmed that the advantage of large males in precopulatory

guarding is related to male-male contests, with larger males being better able to perform take-

overs of already-guarded females (Bel-Venner & Venner, 2006; Bridge et al., 2000).

Furthermore, takeovers resulting from a series of male-male conflicts have likewise been

implicated as the cause of a steady increase in the fighting ability of sequential guarders in the

sierra dome spider (Watson, 1990). As fighting ability has been linked to male body size in P.

clarus, an equivalent increase in fighting intensity is expected to be accompanied by an increase

in the size of guarders relative to roamers in the time approaching the female moult. Lab-based

experiments demonstrating size and weight advantages in male-male contests in P. clarus (Elias

et al., 2008; Hoefler, 2007; Kasumovic et al., 2009, 2010, 2011; Sivalinghem et al., 2010),

further support male-male contests as a likely mechanism for the mid-season mate-guarding size-

advantage.

As suggested by the takeover hypothesis, larger, late-developing P. clarus males may opt

to start guarding later when females are nearest their final moult and thus most valuable. Such a

mechanism would explain the observed size-difference between guarders and roamers mid-

31

season, since the resulting influx of large, competitively superior males into the pool of

perspective guarders would result in the replacement of smaller, early-developing guarding

males who had already started guarding. The absence of the size differential early in the season,

when selection for guarding is relaxed, is also consistent with this hypothesis. Guarding males

found during this time were just as small as roaming males, and male size overall was smaller

than later in the season. Small males may be unlikely to achieve takeovers of paired females later

in the season, but if they are present early in the season, they can begin guarding immature

females before larger males become established (Fig 2.2). By securing early ownership

advantages (Kasumovic et al., 2011), small males may maximize their chance of overcoming

size-disadvantages when challenged by larger, later-maturing males, and thus have the best

chance at defending their position until females moult. Early-season conditions for P. clarus may

be mirrored in the experiment performed by Bel-Venner & Venner (2006), where removal of

direct male-male competition resulted in smaller Z. x-notata males successfully guarding the

webs of females.

The evolution of protandry in this species may be due to selection for early development

arising from the advantage of reaching and establishing residency with valuable virgin females

prior to maturity. However, protandry is expected only if the benefits of early maturation

outweigh selection for large body size, which requires longer development (Maklakov, Bilde, &

Lubin, 2004; Schneider, 1997; Uhl et al., 2004). My results support the idea that this trade-off

may differ for different males. The existence of early-maturing males suggests that opting to

guard early may have some degree of reproductive payoff for inferior males that may be unable

to acquire larger body sizes. Thus the presence of a size differential between guarders and

roamers at the mid- but not early-season is consistent with alternative guarding duration

32

decisions by males based on guarding costs and their own relative competitive abilities, as

described by the takeover hypothesis.

However, there is also support in this study for the fight effort hypothesis, with

intensified male aggression and fighting occurring when guarding offers the highest reproductive

value for males (Enquist & Leimar, 1990; Hurd, 2006; Maynard Smith & Parker, 1976). Males

fighting harder for guarding status near the female’s moult would be expected to result in both an

increased frequency and intensity of size-determined male-male contests and ultimately generate

a size difference between successful and unsuccessful guarders in the absence of alternative male

decision making. Studies of other species have shown male preference for more reproductively

valuable females, be it related to time to maturity (Birkhead & Clarkson, 1980; Mathews, 2003)

or female body size (~fecundity; Bel-Venner & Venner, 2006; Cornet et al., 2012; Lawrence,

1986). Furthermore, empirical and theoretical evidence show increased fighting effort in

response to high resource values (Clutton-Brock, 1989; Enquist & Leimar, 1990; Sigurjónsdóttir

& Parker, 1981) and associations between the rate of turnovers and female value (Bel-Venner,

Dray, Allainé, Menu, & Venner, 2008). Since P. clarus males show preference for larger females

that are closer to moulting (Hoefler, 2008), males may also be more motivated to fight over

guarding these preferred females. An increased turnover rate as a consequence of this intensified

fighting would lead to increases in the size difference between guarders and roamers, particularly

since any successful intruding male is expected to be larger, with higher RHP than the resident

male. Although not measured here, heightened male motivation has been shown to lead to an

increased likelihood of escalation to physical combat (Brown, Chimenti, & Siebert, 2007;

Brown, Smith, Moskalik, & Gabriel, 2006; Nosil, 2002; Simmons, 1986; Tachon, Murray, Gray,

& Cade, 1999) and therefore in a heavier reliance on size-related RHP asymmetries in

33

determining guarding success. However, the absence of a size difference between roamers and

guarders early and late in the season is also consistent with fight effort hypothesis. By this

mechanism, the lower resource value of guarding positions over immature females far from

moult or already-mated females would drastically lower male fighting effort for these positions

and thusly uncouple guarding success from the outcomes of RHP-determined fights.

Since female choice also favours large males (Elias, Sivalinghem, et al., 2010;

Sivalinghem et al., 2010), there exists the additional potential for a size difference between

successful and unsuccessful guarders to be the result of females rejecting and rebuffing potential

guarders based on size (Elias, Botero, Andrade, Mason, & Kasumovic, 2010). Since lab-based

experiments have shown that guarding males experience high mating success if allowed to guard

until female maturation (Elias et al., 2014), selection could act on females to become more

aggressive towards less preferred guarders as females approach their final moult. Although

mature females are large and capable of potentially lethal aggression (Elias, Botero, et al., 2010),

immature females are smaller than most mature males, have relatively small legs, and are not

generally observed to be aggressive (pers obs). I argue that these characteristics, in addition to

the immature female’s position --tightly enclosed within a silken retreat-- make it unlikely that

immature females are capable of effectively fighting adult males. While precopulatory female

choice may be acting in more subtle ways than all-out eviction, the effects of male choice and/or

male-male competition during the period of cohabitation are likely to be primary determinants of

mate-guarding success. Since previous research has focused largely on sexual selection in males

with regards to pre-copulatory mate-guarding however, more research is needed in order to fully

investigate this possibility.

34

Since a goal of this research is to address potential mechanisms involved in determining

mate-guarding success within natural populations of P. clarus, it is important to note that

continuous sampling across the breeding season allows for the potential for collection itself to

alter the population structure and thus the competitive and selective environments under study

here. However, equal sampling effort (time spent searching) the consistent prevalence of both

guarders and roamers in large numbers late into the season when accrued sampling effects would

become a concern (Fig 2.5), indicate that any artefact would likely affect roaming and guarding

males equally. Evidence of a size disparity between guarding and roaming males within mid-

season, against a background of an overall increase in average male size (Fig 2.5) further

suggests that population densities and/or dispersal of males between local populations was

sufficient to maintain the variation in size that would be necessary to detect competitive

processes throughout the entire season. Had the consistent removal of guarding males exhausted

the pool of available large males, the average size of guarding males would be expected to

decrease over time. This not being the case, it is unlikely that collection itself significantly

altered natural conditions.

Although guarding males were larger on average than roaming males late in the season,

this difference was not significant. Previous studies have suggested that late in the season,

mature P. clarus females roam and forage during the day (Hoefler & Jakob, 2006; Sivalinghem

et al., 2010), which is consistent with the lack of strong selection on the size of guarding males

observed in this study (Fig 2.3). However, in contrast to previous reports, I observed males

cohabiting with mature females in retreats well after the period of synchronous female moulting.

Cohabitation with mature females often indicates postcopulatory mate guarding in arthropods

(Calbacho-Rosa, Córdoba-Aguilar, & Peretti, 2010), however extended postcopulatory guarding

35

in P. clarus is unlikely given the tendency for mature females to forage away from the retreat

(Hoefler & Jakob, 2006), and the prediction (based on comparisons to other taxa and protandry)

of male sperm precedence (Hoefler, 2007). I observed pairs copulating as well as cohabiting

beyond the synchronous period of female moult, and since spiders in this study were not marked,

it is therefore possible that these observations represent males mating multiply with the same

female, rather than novel pairings. Studies demonstrating decreased receptivity of mated and

guarded female P. clarus exposed these females to novel males rather than the male with which

they had experience (Elias et al., 2014; Sivalinghem et al., 2010). Thus it is possible that females

maintain receptivity with preferred guarding males, therefore making males found copulating

with females late into the season targets of both inter- and intrasexual selection. Superior males

may stand a better chance of acquiring additional paternity by attempting another mating with

their guarded female, rather than risking locating another, potentially less receptive mated female

found roaming. Evaluating these possibilities will require additional information (rather than just

inferences) about sperm limitation and use patterns in P. clarus, and the number of egg sacs

females are likely to produce in a mating season, as these will determine the value of repeated

copulation with the same female for males (Andrade & Banta, 2002; Wedell, Gage, & Parker,

2002). Regardless of these uncertainties, these observations highlight the importance of female

receptivity patterns, and suggest the potential for both male and female choice to be acting

simultaneously on male reproductive success related to mate-guarding.

However, observations of late-season copulation may also represent males mating with

newly-encountered, mated females. If this is the case, then males can accrue additional

reproductive success during the late-season, and this is not exclusively tied to success in

precopulatory mate-guarding. It has previously been proposed that selection on males following

36

female maturity is primarily determined by female choice directed at courtship display traits

(Hoefler, 2007), which may result in a late-season size-advantage for both cohabiting and

roaming males. This may thus explain the similarity in average body size found between these

two groups during this period in this study (Fig 2.5). The opportunity for males to find and court

additional mated females late in the season is anecdotally supported by my observation of high

densities of mature roaming female (pers obs). Additional longitudinal studies that focus on

female phenology and reproduction are necessary to understand the importance of these

observations.

In conclusion, here I show that male body size is positively correlated with mate guarding

success, but only in the period immediately surrounding the female moult in P. clarus. As male

size in this species has been associated with competitive ability, this pattern fits a common

prediction of the takeover and fight effort hypotheses. Consistent with both these hypotheses,

size differences between guarding and roaming males possibly reflect alternative male decision-

making based on guarding durations and/or heightened levels of male fighting effort in

accordance with the increasing reproductive value of mate guarding. Moreover, relaxed selection

on guarding males early and late in the season, as suggested by the lack of a significant size

difference between guarders and roamers, further emphasizes the importance of female patterns

of receptivity as it relates to the cost and benefits of guarding as a male mating strategy. Mate-

guarding early in the season requires more investment of time and energy, so males may not be

as motivated to obtain guarding positions at this time, and/or large males may mature and

attempt to guard only when females are close to moulting. Similarly relaxed selection on traits

related to successful guarding in the late-season may arise because of alternative opportunities

for copulations with previously-mated females found roaming. While it is difficult to distinguish

37

between the male takeover and fight effort models, these two hypotheses are not necessarily

mutually exclusive, as they are predicted under similar conditions, and are influenced by similar

factors. Here, evidence in support of common predictions nonetheless highlights the importance

of temporal variation in intra- and inter-sexual selection in the evolution of male mating tactics

within natural populations.

38

CHAPTER THREE: MALE COURTSHIP AND FIGHTING

PERFORMANCE AS A FUNCTION OF GUARDING STATUS

Introduction Mate-guarding, an attempt to limit mating access of rival males to females, can depend

on the outcomes in male-male contests (e.g. Benton, 1992; Dodson & Schwaab, 2001; Huffard et

al., 2010). The ability to acquire and defend a resource (in this case, a female), known as

resource holding potential (RHP; G. A. Parker, 1974a), is expected to be correlated with male’s

competitive ability. Body size is often used as a proxy for RHP and fighting ability in various

taxa, since size is often positively correlated with competitive success (Austad, 1983;

Christenson & Goist, 1979; Dodson & Beck, 1993; Hack et al., 1997; R.R. Jackson & Cooper,

1991; Suter & Keiley, 1984; Tedore & Johnsen, 2014). It has likewise been shown that

opponents assess signals of RHP produced by their competitors, either as direct signals, such as

size (Andersson, 1976; Clutton-Brock, Albon, Gibson, & Guinness, 1979; Davies & Halliday,

1979; Turner & Huntingford, 1986)) or indirect ones, such as components of bird songs (DuBois,

Nowicki, & Searcy, 2011; Illes, Hall, & Vehrencamp, 2006), push-up displays in lizards (Van

Dyk, Taylor, & Evans, 2007), and dominant frequencies of frog calls (Bee, Perrill, & Owen,

1999). Game theoretical models predict that relative and self-assessment strategies will evolve

where the likelihood of persisting in a contest is based on information about RHP and the costs

and benefits of winning or losing for each male (G. A. Parker, 1974). Some circumstances, such

as unavoidable receiver error or low costs of being deceived, may lead to the evolution of

unreliable signals of RHP (Gardner & Morris, 1989; Wiley, 1994). However, in systems where

bluffing has significant costs (e.g. physical injury), signals should evolve to convey accurate

information about an individual’s RHP (Maynard Smith & Parker, 1976). It is thus expected that

successful mate-guarding males will be those with higher RHP, and that these males will thus be

39

more likely to win fights either through actual fighting ability or through successfully conveying

information about their fighting ability or motivation to their opponents (Johnstone & Norris,

1993; Vehrencamp, 2000).

Pre-copulatory mate-guarding will increase male fitness only if successful guarders

achieve copulation. The most direct way mate guarding leads to increased mating success is by

preventing other males from mating with females. However if a male’s ability to defend a female

is also correlated with overall male viability (or other female-fitness enhancing traits), mate-

guarding males may also experience higher courtship success through being preferred by

females. In this case, in addition to preventing other males from courting/mating with females,

guarding males may have a higher likelihood of copulating if given the opportunity to court.

Females may thus indirectly benefit if successfully guarding males tend to be of superior genetic

quality (Andersson & Simmons, 2006; Benton, 1992; Härdling et al., 2004; Kokko, Jennions, &

Brooks, 2006; Mead & Arnold, 2004; Prenter et al., 2003). However, females may also pay a

cost of restricted access to preferred mates if males who typically guard successfully do not

possess traits favoured by female choice (Jormalainen, 1998). When mating with a dominant

male comes at a substantial cost to a female (e.g. Petersson, Järvi, Olsén, Mayer, & Hedenskog,

1999; Sih, Lauer, & Krupa, 2002), competition-driven mate-guarding may thus result in sexual

conflict (Wong & Candolin, 2005).

The degree to which mate guarding ensures a high quality mate or limits a female’s capacity

to mate with preferred males depends on the association between male traits providing females

with fitness benefits and those providing males with competitive advantages in gaining access to

females (Wong & Candolin, 2005). When the same traits are used for assessment of genetic

quality by females and of fighting ability by contesting opponents, male-male competition can

40

often benefit a female by having a mate-sorting effect in line with female choice (Review in

Berglund, Bisazza, & Pilastro, 1996). While exceptions have been documented (e.g. Howard,

Moorman, & Whiteman, 1997; McCauley, 1982; Petersson, Järvi, Olsén, Mayer, & Hedenskog,

1999), a large male mating advantage via competitive exclusion is often reinforced by female

preference (Reviewed in Hunt et al., 2009).

In the mating system of the jumping spider Phidippus clarus in which precopulatory mate

guarding has evolved, mature males guard retreating immature females from rival males up until

a period of synchronous female moult. Males able to defend females through male-male contests,

involving stereotyped visual and vibratory signals and escalation to physical combat, secure the

opportunity to court and mate with virgin females.

Laboratory experiments with P. clarus have shown that females favour larger (heavier), more

actively vibrating males (Sivalinghem et al., 2010), and such males are more likely to win fights

(Elias et al., 2008; Elias, Sivalinghem, et al., 2010). However, it is also clear that fight dynamics

can be complex, and may not entirely depend on male morphology (Hofmann & Schildberger,

2001). For example, Watson (1990) found that when size differences between sierra dome spider

males (Linyphia litigiosa: Linyphiidae) are less than 20%, contest outcomes are more likely

determined by vigor or persistence. It has also been suggested that willingness to fight

contributes non-trivially to contest outcomes for opponents with RHP-assymmetries (Hofmann

& Schildberger, 2001). Specific to P. clarus, an advantage of males holding guarding positions

over introduced males in fights (‘ownership’ advantages; Kasumovic et al., 2011) has been

demonstrated to outweigh a positive effect of size on the outcome of fights between males

(Hoefler, 2007; Elias et al., 2008). The result is that guarding males may be able to defeat larger

rivals in individual fights. These fights however, may be escalated and costly, particularly if a

41

rival is relatively large (Kasumovic et al., 2011). Moreover, there are both ‘winner’ and ‘loser’

effects in this species which affect the fighting performance of males as a function of their

success in previous contests (although size has a stronger influence on contest outcomes

(Kasumovic et al., 2009, 2010). There is evidence in other taxa that ‘winner’ or ‘loser’ effects

may also extend to male courtship behaviour and success following fights (Amorim & Almada,

2005).

Due to the synchrony of female maturation in P. clarus, selection via male-male competition

(fighting rival males for guarding positions) and female mate choice (female being receptive to

courtship) is expected to occur sequentially, where the first round of selection via competition

occurs distinctly before selection via female mate choice. The first competition-based bout of

selection on males is expected to be relatively strong, since the overall reproductive success of

males unable to acquire the opportunity to court a virgin female through guarding may be

drastically limited (Hunt et al., 2009). Nevertheless, selection via female mate choice may be

likewise strong in P. clarus since mature females are larger than males and can be highly

aggressive and potentially lethal to males (pers obs), thus making coercive mating unlikely. It is

therefore possible that a successfully guarding male that is not favoured by females could be

chased off or killed by his prospective mate once she matures, creating an opening for other,

more female-choice friendly males. A review by Hunt et al. (2009) found that opposing selection

was more likely to occur when mechanisms operate sequentially, therefore it cannot be assumed

that competitive success is equivalent to mating success and that guarding males are also

favoured by female choice. The reinforcing or opposing relationship between male-male

competition and female choice may have significant implications for the operation of sexual

42

selection on P. clarus as it relates to overall male fitness and thus the evolution of mating

strategies.

Instead of mating advantages purely by competitive exclusion, successfully guarding males

in this species may possess traits that are also preferred by females, and thus experience higher

average courtship success rates given the opportunity to court a mature virgin female (Elias et

al., 2014; Jormalainen, 1998; Neff & Svensson, 2013; D. J. Parker & Vahed, 2010). Regardless

of the specific mechanism, recent laboratory research in P. clarus has shown that indeed

guarding males experience high mating rates with their guarded females (Elias et al., 2014),

reinforcing that mate guarding in this species offers crucial reproductive benefits for males

despite the significant costs associated with this strategy. Indeed, the direct costs associated with

precopulatory mate-guarding may be mitigated if female mate choice reinforces selection via

male-male competition and thus offers indirect benefits for males successful in this strategy. The

fitness gain for successful guarders may be further enhanced by decreased receptivity of mated

and cohabited females to other males (Sivalinghem et al. 2010; Elias et al 2014), and the

synchronous nature of the female maturation period.

While laboratory arena-based male-male contests have shown that larger, heavier and

more actively signalling males tend to win fights, laboratory studies to date have not examined

male performance as a function of their guarding status in the field, so it remains unclear how

selection operates via guarding and female choice in natural populations. This is critical because,

for example, how these winner and loser effects, and strong resident advantages play out in

natural contexts is unclear (Hsu, Earley, & Wolf, 2006). Given the proposed importance of mate-

guarding for male reproductive success as a means to secure access to virgin females, the

objective of this study is to assess the influence of male status in the field on performance within

43

the context of male-male competition and female mate choice. Here I ask whether successfully

guarding males possess traits in addition to size and weight which contribute to RHP and mate

guarding success in nature. Additionally, I hypothesize that successfully guarding males are of

higher genetic quality and will be favoured by female preference. Consequently, I predict that

successful guarders will be more likely to win staged contests against roaming males in part due

to non-size related traits that would give guarding males additional advantages in a highly

competitive environment against rivals possessing similar RHP. I further predict that guarding

males will experience higher courtship success than non-guarders (hereafter “roaming males”)

through correlations between traits favoured by mate guarding and mating success. To test these

predictions I examined the outcome of staged mating opportunities and inter-male competition as

a function of naturally-determined male status (guarder or roamer). This study aims to

investigate the consequences of sexual selection related to mate guarding on male traits

associated with performance in male-male contests and courtship.

Methods

P. clarus reproductive behaviour

Courtship behaviour in P. clarus progresses in a predictable sequence (Hoefler, 2008).

After orientating towards a female, the male elevates its body above the substrate through leg

extension, then proceeds to raise and extend its first pair of (ornamented) legs horizontally. He

then waves these legs vertically in unison, along with an abdominal tremulation, while moving in

a typical jumping spider “zig-zag” motion (Forster, 1982) to slowly approach the female. As the

male approaches, an unreceptive female may raise her body from the substrate by straightening

44

her legs and produce aggressive vibrations with her front legs extended horizontally and fangs

exposed. If the male continues to approach while the female is aggressively displaying, she will

often strike the male with her legs or fangs. However, if a female becomes receptive to a

courting male, she will drop her body to the substrate and retract all of her legs. As this occurs,

the male will extend his front legs and touch the female’s cephalothorax several times while

producing vibrations similar in frequency to the initial vibrations but of longer duration. After

several touches, the male proceeds to mount the female, and if left uninterrupted, will turn her

abdomen to the side so he may insert a pedipalp into one of her two genital openings.

Collection and Housing

All spiders were collected from the University of Toronto’s Koffler Scientific reserve at

Joker’s Hill (see chapter 1 for details). During surveys of fields between June 5th and 23rd 2015,

penultimate-instar virgin females were collected from a field not utilized in other studies (Field

1, figure 2.1; Chapter two). Guarding and roaming males were collected throughout the mating

season as outlined in Chapter 2. Once in the lab, all collected males and females were transferred

into individual AMAC plastic cages (5.87 x 5.87 x 7.78 cm), with opaque dividers to maintain

visual isolation between individuals. Spiders were housed on a light:dark 12 hr cycle at 24 C.

Each cage contained a paper tube, to serve as a retreat, and a tree twig for sensory stimulation in

order to minimize the behavioural effects of lab housing (Carducci & Jakob, 2000). Spiders were

provided with water ad libitum via Eppendorf tubes filled with water and plugged with cotton,

and fed a small cricket (1/4 inch Acheta domesticus) twice weekly. Water tubes were replaced

when empty and cricket carcasses were removed every other week. Cages were checked daily

and the death of any spiders were recorded.

45

Signal Recording

Substrate-borne vibrations produced by males during courtship or male-male contests

were recorded using a Laser Doppler Vibrometer (LDV; Polytec OFV 3001 controller, OFV 511

sensor head) attached to a translation stage (Newport model 421), a procedure used successfully

in several studies of this species (Sivalinghem et al., 2010, Elias et al., 2008). Measured signals

were recorded on a digital VCR (Sony DVCAM DSR-20 digital VCR, 48,1000 kHz sampling

rate, Sony, New York, NY) before being analyzed by Raven Pro 1.4 audio software

(Bioacoustics Research Program, 2011). Small pieces of reflective tape (1 mm2) were placed on

the stretched nylon base of the experimental arena to be measurement points for the LDV.

Courtship Trials

Roaming (nR=37) and guarding (nG=38) males were randomly chosen for single-male

courtship trials (ntotal=75) through a random number generator. As there were not enough virgin

females to use a different female for every trial, females (n = 23) were used multiple times. To

limit the effect of successive trials on female behaviour, no female was used more than once a

day, and females were prevented from mating, and so remained virgins throughout the trials. All

experimental spiders were fed 1 – 2 days before the trial to ensure that hunger did not affect

courtship or aggressive behaviour. The experimental arena was made of nylon stretched over a

needlepoint frame with a transparent acetate plastic wall and an open top. The inside top of the

walls were covered in petroleum jelly to prevent spiders from climbing out. The inside was

cleaned with 70% ethanol between trials to remove any chemicals and silk laid down by previous

spiders. Females and males were both weighed before and after trials using an Ohaus Explorer

balance. Male size was measured post-trial, after males had died on their own as described in

chapter 1.

46

To start a trial, a female was placed in the arena and left to acclimate for 3 minutes before

a male was introduced. An individual male was then added to the arena and both were allowed to

interact freely. Along with LDV recordings, trials were recorded using a video camera recorder

(HANDYCAM®NEX-VG10; Sony e-mount lens SEL18200; 44.1 kHz audio sampling rate).

Males were left in the arena until the male began to mount the female, after the female

receptivity display (contracted legs), or until 10 minutes had elapsed from male introduction. A

10 minute cut-off was used, as has been used in previous lab studies with P. clarus (Elias,

Sivalinghem, et al., 2010; Sivalinghem et al., 2010) since males usually initiate interactions

relatively soon after visually detecting a female (mean latency to courtship initiation = 2.3 min).

Furthermore, males that did not successfully court within 10 minutes tended to either court for

only a small number of bouts or had females continuously aggressively display and strike at

them, either scenario suggesting that courtship was unlikely to be successful if trials were

continued past 10 minutes. After a male began mounting, spiders were separated using a camel-

hair paintbrush and returned to their original cages. Females were given a fresh cricket after

every trial to minimize any potential energetic costs of courtship and therefore reduce (though

potentially not fully removing) the influence courtship experience may have on receptivity in

subsequent trials. Individual females were introduced to males of different status in a random

order (i.e. first and subsequent experiences with a guarder or roamer randomly assigned), and no

female was used more than once per day to further limit the effect of experience.

Competition Trials

To investigate male-male competition, I followed a similar protocol to the courtship

trials, except that two similarly-sized males of opposite status (males collected as guarders or

roamers) were introduced simultaneously to the arena which already contained a virgin female

47

introduced 3 minutes earlier (to remove any resident-advantage, e.g., Kasumovic et al., 2011).

All males used in male-male contests were completely naïve within the laboratory context,

having not been previously used in courtship or competition trials (to avoid effects of courtship

experience, Hoefler, 2008, and winner and loser effects, Kasumovic et al., 2010). To prohibit

direct involvement in male-male interactions, females were placed under a small petri dish.

Females could nevertheless transmit visual and vibratory cues that might evoke competitive

behaviours. Females’ chemical cues were also present since females were allowed to roam freely

in the arena for 3 minutes prior to trials. As game theory predicts (Enquist & Leimar, 1990;

Hurd, 2006; Maynard Smith & Parker, 1976), and empirical studies have shown that males

compete more intensely for highly receptive females (i.e. high resource values; Austad, 1983;

Enquist & Leimar, 1987; Riechert, 1979; Wells, 1988) stimulus females (n= 6 virgin females)

were chosen based on demonstrated high receptivity (never aggressively displayed and accepted

mating attempts from at least one male) in the previous courtship trials. Since females were not

able to directly interact with males, and thus remained virgins, the same female was used in up to

12 consecutive trials. Before each trial, a small amount of nontoxic fluorescent paint was applied

to the dorsal abdominal surface of gently restrained males for identification, using a camel-hair

paintbrush. Males were allowed to interact freely during trials. Typically, males would orient

towards each after being released into the arena. Trials were terminated (1) after 10 minutes if

there were no interactions, or (2) after an interaction that was followed by one male turning 180°

to face away from an opponent and moving away in an apparent attempt to flee. An interaction

was defined as a period during which males were oriented towards each other, involving visual

(front legs raised) and/or vibratory (abdominal tremulations), and often the movement of one

male towards the second male.

48

Signal Analysis

Through analysis of recorded video and laser Doppler vibrometry (LDV), features of

male behaviour and signal displays were measured.

For courtship trials, this included active courtship duration, courtship outcome and

vibration rate (both aggressive- and courtship-type). The start of courtship was defined as the

time when the male initiated some form of courtship display (visual and vibratory or just visual)

while oriented towards the female. The active courtship duration was measured as the total

(summed) time a male spent actively displaying (visual and/or vibratory) while oriented towards

the female throughout the trial. This measure did not include periods of latency between bouts of

displaying where male and female interactions completely stopped. Courtship outcome was

categorized as successful if females displayed a receptivity posture (legs retracted) and

unsuccessful otherwise. Mean pulse durations were calculated from the pulse durations of a

randomly chosen subset (n=5) of recorded vibration pulses and vibration rate was measured as

the total number of pulses divided by courtship time. Signals were qualitatively categorized as

courtship or aggressive signals according to published descriptions (Elias et al., 2008;

Sivalinghem et al., 2010), and separate analyses were performed if both signals were produced in

a single trial. Courtship vibrations are longer in duration and are produced concurrently with a

vertical movements of the first legs (mean duration= 0.71 s) whereas aggressive-type vibrations

occur while the legs are maintained in an elevated position and tend to be of higher amplitude

and much shorter (mean duration=0.11 s), often happening in bouts of 2 or 3.

For competition trials, I scored contest outcome (whether the guarder or roamer

retreated/lost), degree of escalation (occurrence of physical combat), fight initiator (whether

guarding or roaming male was the first to display in a given interaction), active fight duration

49

(summed duration of all displays and/or physical combat) and vibration types and rates for each

male. A retreat, and therefore loss, was scored as when a male turned away from an opponent

following aggressive displays on the part of either males and attempted to run in the other

direction. Average vibration rate calculations were only made when it was clear which spider

was signalling (i.e., overlapping signals were not analyzed). The measurement of an interaction

between males commenced with the first display (visual or vibratory) from at least one male.

Statistical Analyses

Male morphological measurements included in our analyses were (1) composite measures

of male body calculated using principle components analysis (PC1 scores, see Chapter one

methods) and (2) male body condition. To obtain a measure of body condition for males that

incorporated mass, residual values for each male from a significant linear regression of male size

and mass were obtained (Jakob, Marshall, & Uetz, 1996; F1,164= 403.9, p=2..2e-16).

Backwards logistic regression analyses were performed to examine predictors of

courtship and contest success in relation to male status (roaming or guarding). Analysis began

with a complete model that included all measured variables and putative interaction effects that

were determined a priori based on the literature on this species (Table 3.1, Table 3.2). Model

selection involved sequentially dropping the least informative variable in successive steps until a

reduced model was obtained. The model that best represented the data was considered to be the

model with the lowest AIC value. For competition trials, the relationship between fight initiation

and status was analyzed using a chi-square test of independence. All statistical analyses were

two-tailed and performed in R (R Core Team, 2014).

50

Courtship Outcome and Signal Characteristics Related to Status

To assess whether male status (roaming versus guarding) affected courtship success, a

generalized linear mixed model with a binary logistic regression link was used with courtship

success as the outcome variable. The model included random effects of female ID and female

experience (1st, 2nd or 3rd trial for a given female) to account for repeated use of females in trials.

Female experience was included as a random effect since models using female experience as a

fixed effect were unresolved, suggesting that experience does not affect courtship outcome.

Initial models included status, male size, condition, pulse duration, vibration rate, season, and

female mass. I also included interaction factors: status x vibration rate and status x season, where

‘season’ is a factor representing the time of the mating season (early, middle, late) when males

were collected. I also performed several simple linear regressions to explore relationships

between body size and courtship vibration rate, courtship duration, and female mass.

Contest Outcome and Male Characteristics Related to Status

To examine which attributes of male opponents predicted overall contest outcome

(whether the winning male was a guarder or a roamer), I tested several models using either

independent or composite (difference) measures of the traits of competing roaming and guarding

males (mass and vibration rate). Since preliminary analysis revealed that mass and size were

highly correlated (F1,164= 403.9, p=2..2e-16) and previous research has emphasized male mass as

a primary determinant of contest outcomes (Elias et al., 2008; Elias, Sivalinghem, et al., 2010),

size and condition were not included in these models to avoid collinearity. Testing both

independent and composite measures of male traits is consistent with game theory models

suggesting that contest outcomes may depend on self-assessment or relative assessment of RHP,

and other studies suggesting correlates of fight outcomes may include the difference between the

traits of competing males (Hammerstein & Parker, 1982; Maynard Smith & Parker, 1976;

51

Mesterton-Gibbons, Marden, Dugatkin, Biology, & Labs, 1996; G. A. Parker, 1974; Taylor &

Elwood, 2003). In addition to male traits, contest duration, occurrence of escalation, status of

initiating male (guarding versus roaming), and female mass were all included as predictor

variables in the models. Preliminary linear regressions showed that male mass and size were

highly correlated.

To determine whether male status predicts success in male-male contests independent of

other measured traits, one focal male within each contest was randomly chosen for analysis. This

was done to be able to use status as an independent variable while avoiding pseudoreplication

from use of males who fought against one another. The full model initially included contest

outcome (winning versus losing) as the dependent variable and the predictors were: male status,

vibration rate, mass, size and initiation of interactions (yes versus no) by focal individuals. Two-

way interaction terms between status x vibration rate and status x season were also included.

Scalar predictor variables were tested both as absolute values and as the difference between the

focal individual and his opponent. To establish the degree to which body size was correlated with

aggressive vibration rate, I performed a simple linear regression with size as the predictor

variable of vibration rate. I then investigated whether guarding or roaming males were more

likely to initiate a fight, regardless of contest outcome, through a Pearson’s χ2 test of

independence.

Results

Courtship Trials and Signal Characteristics Related to Male Status

The final generalized linear mixed model predicting courtship success included female

mass, courtship duration, vibration rate, season, and an interaction between male status and

vibration rate (Table 3.1). Courtship outcome depended strongly on vibratory signal rate and

52

courtship duration, but there was no significant effect of female mass, nor of the time of season

when males were collected (final model, Table 3.1). Males with higher vibration rates and longer

courtships were more likely to mate regardless of status (Figure 3.1). There was a significant

negative correlation between courtship duration and vibration rate (β=-28.3, p <0.001),

suggesting that males with higher vibration rates mated relatively quickly and that males with

low vibration rates could mate successfully if they persisted sufficiently long in courtship.

Female mass and an interaction between male status and vibration rate were marginally

significant (Table 3.1) so I explored these variables further. Heavier females were more likely to

mate, however this was not because such females are courted more intensely by males. A simple

linear regression revealed no association between male courtship effort (vibration rate or

courtship duration) and female weight (β=0.00448, p=0.917 and β=-1.32, p=0.389, respectively).

The interaction between male status and vibration rate arises because courtship success increases

with vibration rate more steeply for guarding males compared to roaming males (Fig. 3.1).

Overall, except at extremely low vibration rates (<5.0 pulses/min), guarding males tended to be

more successful at courtship than roaming males (Fig. 3.1).

In other studies, male size predicts success in fighting (e.g. Bridge et al., 2000;

Lindstrom, 1988) so we also examined this variable further. Simple linear regression revealed

that body size and courtship vibration rate were significantly positively correlated (F1,59= 4.945,

p=0.03; Fig. 3.2), however body size was not included in the final model as an independent

factor (Table 3.1).

53

Table 3. 1. Predictors of courtship success in laboratory trials of Phidippus clarus males

collected in the field as successful guards or as roamers.

Fixed Effects in Full model Final Model

Male status (roamer-guarder) --

Male size --

Male condition --

Mean pulse duration --

Mean vibration rate F1,54=9.647, p=0.00300*

Female courtship experience --

Courtship duration F1,54=9.679, p=0.00300*

Female mass F1,54=3.545, p=0.0650

Time of season F2,54=2.262, p=0.114

Collection field --

Male status x vibration rate F1,54=3.378, p=0.0720

Male status x time of season -- 1 determined as the model with the lowest AIC following backwards stepwise logistic regression

*Significant at α=0.05

-- denotes factor was dropped in final model

54

Fig. 3. 1. Relationship between courtship success in laboratory trials and the courtship vibration

rate of Phidippus clarus males collected in the field as guarders (dashed line, open circles) or

roamers (solid line, filled circles). Curves are independent logistic regressions to visualize

differences between roamers and guarders in the effect of vibration rate on courtship, using

vibration rate of either roamers or guarders as predictors of courtship success (guarders: β=0.110,

p=0.0615; roamers: β=0.0363, p=0.432).

55

Fig. 3. 2. Relationship between male body size index and courtship vibration rate for Phidippus

clarus males collected in the field as guarders (open circles) or roamers (filled circles). Body size

index is the first principle component of a PCA that includes cephalothorax and first leg

measurements, see Table 2.1, Chapter two).

56

Contest Outcome and Signal Characteristics Related to Male Status

Both Males in Model:

Males competing in male-male contest trials were, on average, similar in size (5%

different in mass). In the final logistic regression model for contests between males, the

aggressive vibration rates of both male opponents significantly predicted the contest outcome

(Table 3.2). A Hosmer-Lemeshow goodness of fit test for the final model showed no evidence of

poor fit (χ2 = 7.76, df = 8, p-value = 0.458). The odds of a male winning were positively

correlated with his own aggressive vibration rate (β=0.195, p=0.0294; Table 3.2) and negatively

correlated to the aggressive vibration rates of his opponent (β=-0.197, p=0.0287). The collection

season of both males, along with presence of escalation remained in the final model, however

none significantly predicted contest outcome (Table 3.2). Replacing individual male phenotypic

and signalling traits in the model with composite (difference) measures of mass and vibration

rates resulted in a similar importance of the relative vibration rate of competitors (Table 3.3,

Figure 3.3). However, when relative values of these variables were used, escalation was a

significant predictor of contest outcome. Contests in which roamers were successful were more

likely to involve escalation than contests won by guarders (β=-2.415, p=0.0462). A Hosmer-

Lemeshow goodness of fit test for this final relative model showed no evidence of poor fit (χ2 =

8.5996, df = 8, p-value = 0.3772).

57

Table 3.2. Predictors of success in laboratory staged male-male competition trials between males

collected as guarders (G) or roamers (R) in nature across the mating season from multiple fields.

Backwards step-wise logistic regression analysis of contest outcomes incorporating absolute

measurements of phenotypic traits for both contestants.

Variables in Full model Final Model 1

Competition duration ---

Female mass ---

Roamer season Early – Mid: β=1.38, p=0.486

Early – Late: β=-1.49, p=0.498

Guarder season Early – Mid: β=1.40, p=0.473

Early – Late: β=3.34, p=0.175

Roamer vibration rate β=-0.197, p=0.0287*

Guarder vibration rate β=0.195, p=0.0294

Roamer mass ---

Guarder mass ---

Escalation β=-2.34, p=0.0703

Initiator ---

Guarder collection field ---

Roamer collection field --- 1 determined as the model with the lowest AIC following backwards stepwise logistic regression

*Significant at α=0.05

58

Table 3. 2. Logistic regression analysis of contest outcomes incorporating relative measurements

of contestants’ phenotypic traits.

Variables in Full model Final Model 1

Competition duration ---

Female weight ----

Roamer season Early – Mid: β=1.36, p=0.488

Early – Late: β=-1.44, p=0.508

Guarder season Early – Mid: β=1.39, p=0.475

Early – Late: β=3.25, p=0.175

Relative vibration rate β=0.195, p=0.0284*

Relative mass ---

Escalation β=-2.41, p=0.0462*

Initiator ---

Guarder collection field ---

Roamer collection field --- 1 determined as the model with the lowest AIC following backwards stepwise logistic regression

*Significant at α=0.05

59

Fig. 3. 3. The relationship between the competitive success of Phidippus clarus males collected

in the field as guarders and roamers, and the relative rate of aggressive vibrations produced

during laboratory competition trials.

60

Focal-Male Model:

Analysis of factors predicting the success of one randomly chosen focal male from each

trial allowed direct tests of the effect of male status on contest outcome. The final model

revealed that focal males were more likely to win if their aggressive vibration rate was high, not

independently of, but relative to, their opponents (Table 3.4, β=0.0032, p=0.764 and Table 3.5,

β=0.134, p=0.0187, respectively). A Hosmer-Lemeshow goodness of fit test for the final model

using absolute values showed no evidence of poor fit (χ2 = 1.4328, df = 8, p-value = 0.9938).

Guarding males were significantly more likely to win contests than roaming males overall (Table

3.4, β=-1.75, p=0.0334) but were only marginally more likely to win if the model included

vibration rate and mass values relative to those of their opponent (Table 3.5; β=-1.44, p=0.0568).

A Hosmer-Lemeshow goodness of fit test for the final relative model using relative values

showed no evidence of poor fit (χ2 = 5.744, df = 7, p-value = 0.5699). There were no significant

interactions between male status and vibration rate (Table 3.4). There was no significant effect of

season on the likelihood of a male winning (Table 3.5).

Unlike courtship vibration rates, there was no significant relationship between male size

and aggressive vibration rates (F1,48=1.848, p=0.181; Fig. 3.4).

61

Table 3. 3. Focal-male analysis of contest outcomes in staged competitive trials between field

collected males using absolute measurements of male phenotypic traits.

Variables in Full model Final Model 1

Male status (R relative to G) β=-1.75, p=0.0334

Male mass ---

Mean pulse duration ---

Mean vibration rate β=0.0032, p=0.764

Escalation Present ---

Initiator ---

Collection field ---

Season (mid relative to early) ---

Season (late relative to early) ---

Male status x vibration rate β=0.0580, p=0.137

Male status x season --- 1 determined as the model with the lowest AIC following backwards stepwise logistic regression

*Significant at α=0.05

Table 3. 4. Focal-male analysis of contest outcomes in staged competitive trials between field

collected males using relative measurements of male phenotypic traits.

Variables in Full model Final Model 1

Male status (R relative to G) β=-1.44, p=0.0568

Relative mass ---

Relative pulse duration ---

Relative vibration rate (G - R) β=0.134, p=0.0187

Escalation Present ---

Initiator ---

Collection field ---

Season (mid relative to early) β=-1.09, p=0.278

Season (late relative to early) β=0.421, p=0.686

Status x vibration rate ---

Status x season --- 1 determined as the model with the lowest AIC following backwards stepwise logistic regression

*Significant at α=0.05

62

Fig. 3. 4. Relationship between aggressive vibration rate and body size of randomly chosen focal

males in competitive contests between Phidippus clarus males collected in the field.

63

Along with guarding males being more successful at winning contests than roaming

males when the model included their absolute values of vibration rate and mass, a chi-squared

test revealed that guarding males were significantly more likely to initiate contests than were

roaming males (guarders: 73.3 % of contests; roamers: 26.7 % of contests; χ2= 9.0909, df = 1, p

= 0.00257).

Discussion

Guarding Male Courtship Success

I hypothesized that successfully guarding males experience greater mating success

through competitive exclusion and by being higher genetic quality males and thus possessing

traits favoured by female choice. I predicted that guarding males would experience higher

courtship success than roaming males, but results from courtship trials revealed that guarding

success did not significantly predict courtship success. However, along with the expected

positive effect of courtship vibration rate on mating success, there was a marginally significant

interaction between status and courtship vibration rate. Guarding males tended to experience a

greater increase in courtship success with increasing vibration rate than roaming males and

tended to have a higher courtship success except at the extremely low vibration rates. This

suggests that guarding success, as determined by the outcome of male-male contests, may also be

associated with signalling traits and potentially the efficacy of their transmission within the

context of courtship. Female use of multiple signals or cues in assessing male quality has been

demonstrated in numerous studies (Bro-Jørgensen, 2010; Johnstone, 1996), and while there are

several theories as to why and how multiple signals have evolved, it is widely believed that they

may facilitate detection and/or improve reception of viability indicators (Candolin, 2003; Iwasa

& Pomiankowski, 1994). Given the complex multimodal nature of P. clarus communication

64

(including visual, vibratory and chemosensory), it is feasible that P. clarus females assess males

through multiple modalities simultaneously and respond differentially to signals depending on

the specific cues presented by a given male. Successfully guarding males with superior fighting

ability may give off specific cues that facilitate better detection of the honest information

contained within vibratory signals, and the presence of these cues may therefore explain the

interaction between vibration rate and status found in this study. One such characteristic of

signals that may influence the transmitting of information contained within male vibration rates

(unmeasured here due to limitations of the experimental setup) is signal intensity. Higher

intensities (measured as amplitude) improve signal reception (Ritschard, Riebel, & Brumm,

2010), and it has been shown in birds, insects, and anurans that females base mating decisions on

song or signal amplitudes in addition to frequencies (Arak, 1988; Castellano, Rosso, Laoretti,

Doglio, & Giacoma, 2000; Latimer & Sippel, 1987). Thus it may be that guarders are able to

produce more intense vibrations relative to their body size and can therefore elicit stronger

female preference for any given vibration rate in comparison to roamers. As vibration rate was

the most significant predictor of mating success, this marginal interactive effect may be non-

trivial to male fitness within the context of a highly competitive and restricted breeding season.

The correlation between, and female preference for, high vibration rates and large body

size found in this and other studies, may mean that guarding males are preferred as mates over

roaming males by virtue of being larger. While guarding success did not directly predict a higher

mating success, it is possible that the larger average size and the better signal reception of

guarding male courtship signals mean that males able to successfully defend immature females

may also be favoured by female choice and thus experience higher likelihoods of courtship

success once females moult. This effect has been observed in the broad-headed skink (Eumeces

65

laticeps), where large males who were shown to exclude smaller males from gaining access to

females were likewise favoured by female choice (Cooper & Vitt, 1993). Moreover, the “good

genes” hypothesis (Hamilton & Zuk, 1982) was implicated as the associative mechanism

between female choice and guarding success in this species, with females using the area of head

colouration as an honest signal of male size (Cooper & Vitt, 1993). As it has been proposed that

courtship-related signals are honest indicators of male quality in P. clarus (Sivalinghem et al.,

2010), the association between these signals and traits important in mate guarding success is

likewise consistent with the “good genes” hypothesis. In addition to possessing superior

competitive abilities, guarding males may be of overall superior quality to their roaming

counterparts. Furthermore, since courtship success is ultimately necessary for the evolution of

male mating strategies, differences in female preference between successful and unsuccessful

guarding males in terms of courtship signal efficacy and body size may be significant in terms of

the selection on male traits related to mate guarding in nature.

Guarding Male Contest Success

Results of male-male contests between roaming and guarding opponents found no

significant effect of weight or size differences between opponents. Given that previous research

has found male mass as an important determinant of contest success (Elias et al., 2011, 2008), it

is possible that the average 5% mass difference between opponents in the present study was not

biologically relevant and therefore undetectable through statistical analysis. Supporting a

minimum threshold for an effect of mass/size differences on contest outcomes, Hack et al. (1997)

demonstrated that size-advantages disappeared when size asymmetries dropped below 10%

between opponents of the mate guarding orb-weaver spider M. segmentata.

66

Despite not finding results consistent with previous research on the effect of male size in

staged contests, the significantly larger average size of guarding males found in the field

suggests that this may be an important determinant of mate-guarding success in this species

when size differences are above a specific threshold. Body size has been shown to be an

indicator of RHP, in the context of mate guarding, in various taxa (Austad, 1983; Briffa, 2008;

Clutton-Brock et al., 1979; Wells, 1988). In a study on the scorpion Euscorpius flavicaudis,

Benton (1992) found that larger and stronger males tended to initiate and win more fights, thus

allowing them to hold on to guarding positions for longer. Consequences for mate-guarding of

size asymmetries have likewise been predicted by game theory models, where opponents may

use assessment of resource value and relative or self-assessment of RHP to inform strategic

decisions (Enquist & Leimar, 1983, 1987; Hammerstein & Parker, 1982; G. A. Parker, 1974).

Differences in body size or weight can often be the source of asymmetries in RHP, and this has

been shown empirically within the context of agonistic contests over resources such as territories

and retreat sites (Englund & Olsson, 1990; Lindström & Pampoulie, 2005; Polak, 1994; Reichert

& Gerhardt, 2011; Wells, 1988) and in P. clarus specifically, over mates (Elias et al., 2008;

Kasumovic et al., 2009). Given evidence based on both theoretical and empirical studies, larger,

heavier P. clarus males are predicted to have greater fighting abilities and thus a better ability to

over-come ownership and experience effects of resident males to obtain and defend guarding

positions.

After controlling for the previously established size and weight advantage in male-male

contests, results from this study suggest that aggressive male vibration rate is the most important

predictor of fight success (Table 3.2, 3.3, 3.5). This is consistent with results from previous

studies assessing male competition in P. clarus, where likelihood of winning increased with

67

increasing vibration rate, and likewise with increasing asymmetries in favour of the higher

vibrating male (Elias et al., 2008). Interestingly however, guarding males were still more likely

to win contests even after controlling for vibration rate (Table 3.4). Contrasted with the effect of

vibration rate within a courtship context, the effect of aggressive vibration rate on contest

outcome was not influenced by status (Table 3.4), and aggressive vibration rate was not

significantly correlated with male size. This suggests that the competitive advantage guarding

males possess is not exclusively related to vibratory aspects of a male’s aggressive display,

despite the importance of these signals in the outcomes of staged contests. A greater size

asymmetry between males may have allowed for statistical analysis to detect the correlation

between male size and vibration rate and its influence on contest outcomes. Given the high

density of males during the breeding season and of male size variation, it is likely that in nature

males encounter competitors of all sizes, and thus that size-related vibrational advantages in male

interactions may play a significant role in guarding success. This is even more likely given the

size disparity found between guarding and roaming males (Chapter two).

While results from Chapter two, indicate that male body size and signals containing

information on size (vibration rate) are key factors in determining guarding success, a significant

guarder advantage in male-male fights (Table 3.4) suggests that guarders possess additional traits

contributing to their success. Consistent with the observed fighting advantage after controlling

for size, inherent size-independent components of RHP have been proposed in previous studies

in the absence of a predicted size-advantage in male-male contests (e.g. Reichert & Gerhardt,

2011; Sigurjónsdóttir & Parker, 1981). The absence of a significant interaction between status

and aggressive vibration rate suggests the presence of other guarder traits providing additional

advantages in contests beyond those conveyed by size. There is no clear evidence that guarders

68

are able to produce better, or more effective, aggressive signals as has been suggested in the case

of courtship. Non-vibratory characteristics of guarders may include a higher fight motivation,

which would explain the significantly higher likelihood of guarders initiating fights compared

with roamers. As threat displays may function to transmit information on aggressive motivation

and intentions in addition to direct fighting ability (Hofmann & Schildberger, 2001), a higher

propensity to initiate aggressive displays may play a role in the success of guarding P. clarus

males in nature.

Along with other components of RHP (i.e. size), males may use assessment of

motivational states during encounters in decisions of whether to escalate or retreat (Hofmann &

Schildberger, 2001) and studies have demonstrated that high motivation may enable males to win

against larger opponents (Kotiaho, Alatalo, Mappes, & Parri, 1999; Wagner, 1989). While the

propensity to initiate did not directly translate into contest success here, this trait may give

guarding males an additional advantage where pre-determined males are not forced to interact

within staged contests. The increased likelihood of a roaming male winning once a fight

escalated to true physical fighting between opponents of similar RHP seems to support this idea,

whereby only roaming males possessing comparable RHP would choose to escalate in the face of

an initiating guarding male. When RHP-matched intruding and resident males interact in natural

settings, initial aggressive visual displays conveying information both on willingness to fight and

on body size (via presentation of leg span and tibial brushes) may play a larger role in

determining the outcome of male-male contests than in enclosed arena-based experiments. As it

has been suggested that the importance of body size could be over-estimated in staged

encounters between males (Lindström & Pampoulie, 2005), more research is required to address

this possibility.

69

Overall, the results indicate that guarding and courtship success are correlated, where

males who are successful at guarding in the field also experience heightened courtship success

with females encountered within staged experiments. The observed association between traits

favoured in both contexts suggest that females may also benefit from this mating strategy,

whereby competition facilitates mating opportunities with preferred mates for females. Guarders

do better in both contexts mainly because they are larger and have higher vibration rates.

However, a disproportionate gain from vibratory signal increases within a courtship context and

a size-independent advantage in male-male contests suggests that other inherent traits of guarders

not captured by these analyses may be related to their success in natural field conditions. Given

the capacity for resource value, ownership advantages, experience effects, and readiness to fight

to significantly influence the outcome of male-male contest (Dodson & Schwaab, 2001; Elias et

al., 2008; Enquist & Leimar, 1987; Hack et al., 1997; Hofmann & Schildberger, 2001; Hsu &

Wolf, 2001; Kasumovic et al., 2011), the higher likelihood of guarders to initiate contests may be

associated with size-independent traits that enhance the mate-guarding advantages of larger,

more actively vibrating males in nature.

70

CHAPTER 4: GENERAL CONCLUSION

Results from Chapter two found evidence consistent with selection through precopulatory

mate-guarding favouring large body size in P. clarus males. In conjunction with a large-male

advantage in staged contests (Elias et al., 2008; Hoefler, 2007; Kasumovic et al., 2009, 2010,

2011; Sivalinghem et al., 2010), these findings implicate the role of size-determined outcomes

of direct male-male competition in mate-guarding success in the field. Guarders were

significantly larger than roamers exclusively around the period of female moult. This is expected

if there is heightened competition for guarding positions with females who are close to moulting.

The observed variation in size disparity between guarders and roamers across the season is

consistent with predictions of both the takeover and fight effort hypotheses. Evidence in support

of mutual predictions from these hypotheses suggest that the importance of takeovers between

males and thus direct male-male contests on mate-guarding success in P. clarus is directly tied to

the heightened reproductive value for males of females surrounding their final moult. Given the

protandry in this species and the opportunities for additional matings through courtship instead

of guarding, relaxed selection on male size in mate guarding success early and late in the season

emphasizes the importance of different and potentially opposing selective forces that can interact

to drive the evolution of male mating strategies.

I examined the consequences of such shifting opportunities for male-male competition

and female choice by assessing the association between mate guarding success and male

performance in courtship and competitive contexts. These studies revealed that male signalling

traits determined courtship and contest success. Vibration rates of males predicted courtship and

male-male contest success, the outcomes of which favour more actively vibrating males. As

vibration rates are significantly correlated with male size in both contexts, these results provide

further evidence for the role of male size in mate guarding success in the field and suggest that

71

selection via female choice may reinforce the filtering effect of male competition. In some cases,

mate guarding represents a form of sexual conflict, through for example, disproportionate costs

of guarding to one sex or the exclusion of preferred mates (Arnqvist, 1988; Hirotani, 1994).

However, my results indicate that mate-guarding in P. clarus may offer mutual benefits to males

and females, whereby small, presumably poor-quality males disfavoured by female preference

are denied mating opportunities through competitive exclusion.

While evidence suggests that larger males experience higher guarding success surrounding

the period of female moult and that this selection may be the consequence of direct size-related

male-male contests, guarding males seem to possess traits independent of size that result in some

degree of additional advantages in both courtship and competitive contexts. As guarders

produced marginally more effective courtship signals and were more likely to initiate and win

male-male contests independent of size, processes determining mate guarding success in the field

are likely complex and influenced by the interaction of multiple phenotypic and behavioural

traits. Together, the strong influence of seasonal timing on size-related sexual selection through

mate-guarding with the added presence of size-independent traits conferring guarding advantages

stress the importance of variable environmental conditions and non-static traits on the processes

of sexual selection and their impact on the evolution of reproductive tactics.

72

REFERENCES

Adams, J., & Greenwood, P. J. (1983). Why are males bigger than females in pre-copula pairs of Gammarus pulex? Behavioral Ecology and Sociobiology, 13(4), 239–241. http://doi.org/10.1007/BF00299670

Alberts, S. C., Altmann, J., & Wilson, M. L. (1996). Mate guarding constrains foraging activity of male Baboons. Animal Behaviour, 51(Enomoto 1974), 1269–1277. http://doi.org/10.1006/anbe.1996.0131

Alonso-Alvarez, C., Doutrelant, C., & Sorci, G. (2004). Ultraviolet reflectance affects male-male interactions in the blue tit (Parus caeruleus ultramarinus). Behavioral Ecology, 15(5), 805–809. http://doi.org/10.1093/beheco/arh083

Amorim, M. C. P., & Almada, V. C. (2005). The outcome of male-male encounters affects subsequent sound production during courtship in the cichlid fish Oreochromis mossambicus. Animal Behaviour, 69(3), 595–601. http://doi.org/10.1016/j.anbehav.2004.06.016

Andersson, M. (1976). Social behaviour and communication in the Great Skua, 58(1), 40–77.

Andersson, M. (1982). Sexual selection , natural selection and quality advertisement. Biological Journal of the Linnean Society, 82, 375–393.

Andersson, M. (1994). Sexual Selection. Princeton: Princeton University Press.

Andersson, M., & Iwasa, Y. (1996). Sexual selection. Trends in Ecology and Evolution, 11, 53–58.

Andersson, M., & Simmons, L. W. (2006). Sexual selection and mate choice. Trends in Ecology and Evolution, 21(6), 296–302. http://doi.org/10.1016/j.tree.2006.03.015

Andrade, M. C. B. B., & Banta, E. M. (2002). Value of male remating and functional sterility in redback spiders. Animal Behaviour, 63(5), 857–870. http://doi.org/DOI: 10.1006/anbe.2002.2003

Arak, A. (1988). Female mate selection in the natterjack toad: active choice or passive atraction? Behavioral Ecology and Sociobiology, 22(5), 317–327. http://doi.org/10.1007/BF00295100

Arakaki, N., Kishita, M., Nagayama, A., Fukaya, M., Yasui, H., Akino, T., … Wakamura, S. (2004). Precopulatory mate guarding by the male green chafer, Anomala albopilosa sakishimana Nomura (Coleoptera: Scarabaeidae). Applied Entomology and Zoology, 39(3), 455–462. http://doi.org/10.1303/aez.2004.455

Arnqvist, G. (1988). Mate guarding and sperm displacement in the water strider Gerris lateralis Schumm. (Heteroptera: Gerridae). Freshwater Biology, 19(2), 269–274. http://doi.org/10.1111/j.1365-2427.1988.tb00347.x

Austad, S. N. (1982). First male sperm priority in the bowl and doily spider, Frontinella pyrmaitela (Walkcenaer). Evolution, 36(4), 777–785.

73

Austad, S. N. (1983). A game theoretical interpretation of male combat in the bowl and doily spider (Frontinella pyramitela). Animal Behaviour, 31(1), 59–73. http://doi.org/10.1016/S0003-3472(83)80173-0

Bauer, R. T., & Abdalla, J. H. (2001). Male mating tactics in the shrimp Palaemonetes pugeo (Decapoda, Caridea): Precopulatory mate guarding vs. pure searching. Ethology, 107, 185–199. Retrieved from http://onlinelibrary.wiley.com/doi/10.1046/j.1439-0310.2001.00631.x/full

Bee, M. a., Perrill, S. a., & Owen, P. C. (1999). Size assessment in simulated territorial encounters between male green frogs (Rana clamitans). Behavioral Ecology and Sociobiology, 45(3-4), 177–184. http://doi.org/10.1007/s002650050551

Bel-Venner, M. C., Dray, S., Allainé, D., Menu, F., & Venner, S. (2008). Unexpected male choosiness for mates in a spider. Proceedings. Biological Sciences / The Royal Society, 275(1630), 77–82. http://doi.org/10.1098/rspb.2007.1278

Bel-Venner, & Venner, S. (2006). Mate-guarding strategies and male competitive ability in an orb-weaving spider: results from a field study. Animal Behaviour, 71(6), 1315–1322. http://doi.org/10.1016/j.anbehav.2005.08.010

Benton, T. G. (1992). Determinants of male mating success in a scorpion. Animal Behaviour, 43(1), 125–135. http://doi.org/10.1016/S0003-3472(05)80078-8

Berglund, A., Bisazza, A., & Pilastro, A. (1996). Armaments and ornaments : an evolutionary explanation of traits of dual utility. Biological Journal of the Linnean Society, 58, 385–399.

Berrill, M., & Arsenault, M. (1984). The breeding behaviour of a northern temperate orconectid crayfish, Orconectes rusticus. Animal Behaviour, 32(2), 333–339. http://doi.org/10.1016/S0003-3472(84)80265-1

Birkhead, T. R., & Clarkson, K. (1980). Mate Selection and Precopulatory Guarding in Gammarus pulex. Zeitschrift Für Tierpsychologie, 52(4), 365–380. http://doi.org/10.1111/j.1439-0310.1980.tb00724.x

Birkhead, T. R., & Møller, A. P. (1992). Sperm Competition in Birds: Evolutionary Causes and Consequences. (J. T. A. Dick, Ed.). London: Academic Press.

Bonduriansky, R., & Rowe, L. (2003). Interactions among mechanisms of sexual selection on male body size and head shape in a sexually dimorphic fly. Evolution; International Journal of Organic Evolution, 57(9), 2046–2053. http://doi.org/10.1554/03-047

Bridge, a P., Elwood, R. W., & Dick, J. T. (2000). Imperfect assessment and limited information preclude optimal strategies in male-male fights in the orb-weaving spider Metellina mengei. Proceedings. Biological Sciences / The Royal Society, 267(1440), 273–279. http://doi.org/10.1098/rspb.2000.0997

74

Briffa, M. (2008). Decisions during fights in the house cricket, Acheta domesticus: mutual or self assessment of energy, weapons and size? Animal Behaviour, 75(3), 1053–1062. http://doi.org/10.1016/j.anbehav.2007.08.016

Bro-Jørgensen, J. (2010). Dynamics of multiple signalling systems: animal communication in a world in flux. Trends in Ecology and Evolution, 25(5), 292–300. http://doi.org/10.1016/j.tree.2009.11.003

Brown, W. D., Chimenti, A. J., & Siebert, J. R. (2007). The payoff of fighting in house crickets: Motivational asymmetry increases male aggression and mating success. Ethology, 113(5), 457–465. http://doi.org/10.1111/j.1439-0310.2007.01357.x

Brown, W. D., Smith, A. T., Moskalik, B., & Gabriel, J. (2006). Aggressive contests in house crickets: size, motivation and the information content of aggressive songs. Animal Behaviour, 72(1), 225–233. http://doi.org/10.1016/j.anbehav.2006.01.012

Calbacho-Rosa, L., Córdoba-Aguilar, A., & Peretti, A. (2010). Occurrence and duration of post-copulatory mate guarding in a spider with last sperm precedence. Behaviour, 147(10), 1267–1283. http://doi.org/10.1163/000579510X514544

Caldwell, R. L., & Dingle, J. (1979). The influence of size differential on agonistic encounters in the mantis shrimp, Gonodactylus viridis. Behaviour, 69(3), 255–264. http://doi.org/10.1163/156853979X00502

Candolin, U. (2003). The use of multiple cues in mate choice. Biological Reviews of the Cambridge Philosophical Society, 78(4), 575–595. http://doi.org/10.1017/S1464793103006158

Carducci, J., & Jakob, E. (2000). Rearing environment affects behaviour of jumping spiders. Animal Behaviour, 59(1), 39–46. http://doi.org/10.1006/anbe.1999.1282

Castellano, S., Rosso, A., Laoretti, F., Doglio, S., & Giacoma, C. (2000). Call intensity and female preferences in the European green toad. Ethology, 106(12), 1129–1141. http://doi.org/10.1046/j.1439-0310.2000.00639.x

Christenson, T. E., & Goist, K. C. (1979). Costs and benefits of male-male competition in the orb weaving spider, Nephila clavipes. Behavioral Ecology and Sociobiology, 5(1), 87–92. http://doi.org/10.1007/BF00302697

Chuang-Dobbs, H. C., Webster, M. S., & Holmes, R. T. (2001). The effectiveness of mate guarding by male black-throated blue warblers. Behavioral Ecology, 12(5), 541–546. http://doi.org/10.1093/beheco/12.5.541

Clark, D. L., & Morjan, C. L. (2001). Attracting female attention: the evolution of dimorphic courtship displays in the jumping spider Maevia inclemens (Araneae: Salticidae). Proceedings. Biological Sciences / The Royal Society, 268(1484), 2461–2465. http://doi.org/10.1098/rspb.2001.1819

Clutton-Brock, T. H. (1989). Review Lecture: Mammalian Mating Systems. Proceedings of the Royal Society B: Biological Sciences, 236(1285), 339–372. http://doi.org/10.1098/rspb.1989.0027

75

Clutton-Brock, T. H., Albon, S. D., Gibson, R. M., & Guinness, F. E. (1979). The logical stag: Adaptive aspects of fighting in red deer (Cervus elaphus L.). Animal Behaviour, 27, 211–225. http://doi.org/10.1016/0003-3472(79)90141-6

Cooper, W. E. (1999). Tradeoffs between courtship, fighting, and antipredatory behavior by a lizard, Eumeces laticeps. Behavioral Ecology and Sociobiology, 47(1-2), 54–59. http://doi.org/10.1007/s002650050649

Cooper, W. E., & Vitt, L. J. (1993). Female mate choice of large male broadheaded skinks. Animal Behaviour, 43, 683–693.

Cornet, S., Luquet, G., & Bollache, L. (2012). Influence of female moulting status on pairing decisions. Journal of Zoology, 286, 312–319. http://doi.org/10.1111/j.1469-7998.2011.00882.x

Crane, J. (1949). Comparative biology of salticid spiders at Rancho Grande, Venezuela. Part IV. An analysis of display. Zoologica, 34, 159–215.

Danielsson, I. (2001). Antagonistic pre- and post-copulatory sexual selection on male body size in a water strider (Gerris lacustris). Proceedings. Biological Sciences / The Royal Society, 268(1462), 77–81. http://doi.org/10.1098/rspb.2000.1332

Darwin, C. (1859). On the Origin of Species by Means of Natural Selection. (J. Murray, Ed.). London.

Darwin, C. (1871). The Descent of Man and Selection in Relation to Sex. (J. Murray, Ed.). London.

Davies, N. B., & Halliday, T. R. (1979). Competitive mate searching in male common toads, Bufo bufo. Animal Behaviour, 27(April 1978), 1253–1267. http://doi.org/10.1016/0003-3472(79)90070-8

Dodson, G. N., & Beck, M. W. (1993). Pre-copulatory guarding of penultimate females by male crab spiders, Misumenoides formosipes. Animal Behaviour, 46, 951–959.

Dodson, G. N., & Schwaab, A. T. (2001). Body size, leg autotomy, and prior experience as factors in the fighting success of male crab spiders, Misumenoides formosipes. Journal of Insect Behavior, 14(6), 841–855. http://doi.org/10.1023/A:1013045602493

Donaldson, W. E., & Adams, A. E. (1989). Ethogram of behavior with emphasis on mating for the Tanner crab Chionecetes bairdi Rathbun. Journal of Crustacean Biology, 9(1), 37–53. http://doi.org/10.1163/20021975-99990364

DuBois, A. L., Nowicki, S., & Searcy, W. a. (2011). Discrimination of vocal performance by male swamp sparrows. Behavioral Ecology and Sociobiology, 65(4), 717–726. http://doi.org/10.1007/s00265-010-1073-2

Elgar, M. a, De Crespigny, F. E. C., & Ramamurthy, S. (2003). Male copulation behaviour and the risk of sperm competition. Animal Behaviour, 66, 211–216. http://doi.org/10.1006/anbe.2003.2189

76

Elias, D. O., Andrade, M. C. B., & Kasumovic, M. M. (2011). Dynamic Population Structure and the Evolution of Spider Mating Systems. Spider Physiology and Behaviour (1st ed., Vol. 41). Elsevier Ltd. http://doi.org/10.1016/B978-0-12-415919-8.00002-1

Elias, D. O., Botero, C. a., Andrade, M. C. B., Mason, A. C., & Kasumovic, M. M. (2010). High resource valuation fuels “desperado” fighting tactics in female jumping spiders. Behavioral Ecology, 21(4), 868–875. http://doi.org/10.1093/beheco/arq073

Elias, D. O., Kasumovic, M. M., Punzalan, D., Andrade, M. C. B., & Mason, A. C. (2008). Assessment during aggressive contests between male jumping spiders. Animal Behaviour, 76(3), 901–910. http://doi.org/10.1016/j.anbehav.2008.01.032

Elias, D. O., Sivalinghem, S., Mason, A. C., Andrade, M. C. B., & Kasumovic, M. M. (2010). Vibratory communication in the jumping spider Phidippus clarus: Substrate-borne courtship signals are important for male mating success. Ethology, 116(10), 990–998. http://doi.org/10.1111/j.1439-0310.2010.01815.x

Elias, D. O., Sivalinghem, S., Mason, A. C., Andrade, M. C. B., & Kasumovic, M. M. (2014). Mate-guarding courtship behaviour: tactics in a changing world. Animal Behaviour, 97, 25–33. http://doi.org/10.1016/j.anbehav.2014.08.007

Elwood, R. W., & Dick, J. T. a. (1990). The amorous Gammarus: the relationship between precopula duration and size-assortative mating in G. pulex. Animal Behaviour, 39(5), 828–833. http://doi.org/10.1016/S0003-3472(05)80946-7

Englund, G., & Olsson, T. I. (1990). Fighting and assessment in the net-spinning caddis larva Arctopsyche ladogensis: a test of the sequential assessment game. Animal Behaviour, 39(1), 55–62. http://doi.org/10.1016/S0003-3472(05)80725-0

Enquist, M., & Leimar, O. (1983). Evolution of fighting behaviour: Decision rules and assessment of relative strength. Journal of Theoretical Biology, 102(3), 387–410. http://doi.org/10.1016/0022-5193(83)90376-4

Enquist, M., & Leimar, O. (1987). Evolution of fighting behaviour: The effect of variation in resource value. Journal of Theoretical Biology, 127(2), 187–205. http://doi.org/10.1016/S0022-5193(87)80130-3

Enquist, M., & Leimar, O. (1990). The evolution of fatal fighting. Animal Behaviour, 39(1), 1–9. http://doi.org/10.1016/S0003-3472(05)80721-3

Estrada, C., Yildizhan, S., Schulz, S., & Gilbert, L. E. (2010). Sex-specific chemical cues from immatures facilitate the evolution of mate guarding in Heliconius butterflies. Proceedings. Biological Sciences / The Royal Society, 277(1680), 407–413. http://doi.org/10.1098/rspb.2009.1476

Fahey, B. F., & Elgar, M. a. (1997). Sexual cohabitation as mate-guarding in the leaf-curling spider Phonognatha graeffei keyserling (Araneoidea, Araneae). Behavioral Ecology and Sociobiology, 40(2), 127–133. http://doi.org/10.1007/s002650050325

77

Forster, L. (1982). Visual communication in jumping spiders (Salticidae). In J. S. Witt, P. N.Rovner (Ed.), Spider Communication: Mechanisms and Ecological Significance (p. 161—212). Princeton: Princeton University Press.

Galimberti, F., Sanvito, S., Braschi, C., & Boitani, L. (2007). The cost of success: Reproductive effort in male southern elephant seals (Mirounga leonina). Behavioral Ecology and Sociobiology, 62(2), 159–171. http://doi.org/10.1007/s00265-007-0450-y

Gardner, R., & Morris, M. R. (1989). The evolution of bluffing in animal contests: An ESS aproach. Journal of Theoretical Biology, 137, 235–243.

Girard-Buttoz, C., Heistermann, M., Rahmi, E., Marzec, A., Agil, M., Fauzan, P. A., & Engelhardt, A. (2014). Mate-guarding constrains feeding activity but not energetic status of wild male long-tailed macaques (Macaca fascicularis). Behavioral Ecology and Sociobiology, 68(4), 583–595. http://doi.org/10.1007/s00265-013-1673-8

Grafen, A., & Ridley, M. (1983). A model of mate guarding. Journal of Theoretical Biology, 102(4), 549–567. http://doi.org/10.1016/0022-5193(83)90390-9

Hack, M., Thompson, D., & Fernandes, D. (1997). Fighting in males of the autumn spider, Metellina segmentata: effects of relative body size, prior residency and female value on contest outcome and duration. Ethology, 103(1097), 488–498. http://doi.org/10.1111/j.1439-0310.1997.tb00162.x

Hamilton, W. D., & Zuk, M. (1982). Heritable true fitness and bright birds: a role for parasites? Science, 218(4570), 384–387. http://doi.org/10.1126/science.7123238

Hammerstein, P., & Parker, G. A. (1982). The asymmetric war of attrition. Journal of Theoretical Biology, 96(4), 647–682. http://doi.org/10.1016/0022-5193(82)90235-1

Härdling, R., Kokko, H., & Elwood, R. W. (2004). Priority versus brute force: when should males begin guarding resources? The American Naturalist, 163(2), 240–252. http://doi.org/10.1086/381043

Harts, A. M. F., & Kokko, H. (2013). Understanding promiscuity: When Is seeking additional mates better than guarding an already found one? Evolution, 67(10), 2838–2848. http://doi.org/10.1111/evo.12163

Hill, D. E. (2014). Notes on the jumping spider Phidippus clarus Keyserling 1885 ( Araneae : Salticidae : Dendryphantinae ). Peckhamia, 113(1), 1–32.

Hirotani, A. (1994). Dominance rank, copulatory behaviour and estimated reproductive success in male reindeer. Animal Behaviour. http://doi.org/10.1006/anbe.1994.1318

Hoefler, C. D. (2007). Male mate choice and size-assortative pairing in a jumping spider, Phidippus clarus. Animal Behaviour, 73(6), 943–954. http://doi.org/10.1016/j.anbehav.2006.10.017

Hoefler, C. D. (2008). The costs of male courtship and potential benefits of male choice for large mates in Phidippiis clarus ( Araneae , Salticidae ). The Journal of Arachnology, 36, 210–212.

78

Hoefler, C. D., & Jakob, E. M. (2006). Jumping spiders in space: movement patterns, nest site fidelity and the use of beacons. Animal Behaviour, 71(1), 109–116. http://doi.org/10.1016/j.anbehav.2005.03.033

Hofmann, H. a, & Schildberger, K. (2001). Assessment of strength and willingness to fight during aggressive encounters in crickets. Animal Behaviour, 62(2), 337–348. http://doi.org/10.1006/anbe.2001.1746

Holdsworth, A. R., & Morse, D. H. (2000). Mate guarding and aggression by the crab spider Misumena vatia in relation to female reproductive status and sex ratio. The American Midland Naturalist, 143(1), 201–211. http://doi.org/10.1674/0003-0031(2000)143[0201:MGAABT]2.0.CO;2

Howard, R. D., Moorman, R. S., & Whiteman, H. H. (1997). Differential effects of mate competition and mate choice on eastern tiger salamanders. Animal Behaviour, 53, 1345–1356.

Hsu, Y., Earley, R. L., & Wolf, L. L. (2006). Modulation of aggressive behaviour by fighting experience: mechanisms and contest outcomes. Biological Reviews of the Cambridge Philosophical Society, 81(1), 33–74. http://doi.org/10.1017/S146479310500686X

Hsu, Y., & Wolf, L. L. (2001). The winner and loser effect: what fighting behaviours are influenced? Animal Behaviour, 61(4), 777–786. http://doi.org/10.1006/anbe.2000.1650

Huffard, C. L., Caldwell, R. L., & Boneka, F. (2010). Male-male and male-female aggression may influence mating associations in wild octopuses (Abdopus aculeatus). Journal of Comparative Psychology, 124(1), 38–46. http://doi.org/10.1037/a0017230

Hunt, J., Breuker, C. J., Sadowski, J. a., & Moore, A. J. (2009). Male-male competition, female mate choice and their interaction: Determining total sexual selection. Journal of Evolutionary Biology, 22(1), 13–26. http://doi.org/10.1111/j.1420-9101.2008.01633.x

Hurd, P. L. (2006). Resource holding potential, subjective resource value, and game theoretical models of aggressiveness signalling. Journal of Theoretical Biology, 241(3), 639–648. http://doi.org/10.1016/j.jtbi.2006.01.001

Illes, A. E., Hall, M. L., & Vehrencamp, S. L. (2006). Vocal performance influences male receiver response in the banded wren. Proceedings. Biological Sciences / The Royal Society, 273(1596), 1907–1912. http://doi.org/10.1098/rspb.2006.3535

Iwasa, Y., & Pomiankowski, A. (1994). The evolution of mate preferences for multiple sexual ornaments. Evolution, 48(3), 853–867. http://doi.org/10.2307/2410492

Iyengar, V. K., & Starks, B. D. (2008). Sexual selection in harems: Male competition plays a larger role than female choice in an amphipod. Behavioral Ecology, 19(3), 642–649. http://doi.org/10.1093/beheco/arn009

79

Jackson, R. R. (1982). The behaviour of communicating in jumping spiders. In J. S. Rovner (Ed.), Spider communication: mechanisms and ecological significance (pp. 213–247). Princeton: Princeton University Press.

Jackson, R. R. (1986). Cohabitation of males and juvenile females: a prevalent mating tactic of spiders. Journal of Natural History, 20(5), 1193–1210. http://doi.org/10.1080/00222938600770791

Jackson, R. R., & Cooper, K. J. (1991). The influence of body size and prior residency on the outcome of male-male interactions of Marpissa marina, a New Zealand jumping spider (Araneae Salticidae). Ethology Ecology & Evolution, 3(1), 79–82. http://doi.org/10.1080/08927014.1991.9525391

Jakob, E. M., Marshall, S. D., & Uetz, G. W. (1996). Estimating fitness : A comparison of body condition indices. Oikos, 77(1), 61–67.

Johnsen, A., Lifjeld, J. T., & Krokene, C. (2003). Age-related variation in mate-guarding intensity in the bluethroat (Luscinia s. svecica). Ethology, 109(2), 147–158. http://doi.org/10.1046/j.1439-0310.2003.00861.x

Johnstone, R. A. (1996). Multiple displays in animal communication:`Backup signals’ and `multiple messages'. Philosophical Transactions of the Royal Society B: Biological Sciences, 351(1337), 329–338. http://doi.org/10.1098/rstb.1996.0026

Johnstone, R. A., & Norris, K. (1993). Badges of status and the cost of aggression. Behavioral Ecology and Sociobiology, 32(2), 127–134. http://doi.org/10.1007/BF00164045

Jormalainen, V. (1998). Precopulatory mate guarding in crustaceans: Male competitive strategy and intersexual conflict, 73(3), 275–304.

Kasumovic, M. M., Elias, D. O., Punzalan, D., Mason, A. C., & Andrade, M. C. B. (2009). Experience affects the outcome of agonistic contests without affecting the selective advantage of size. Animal Behaviour, 77(6), 1533–1538. http://doi.org/10.1016/j.anbehav.2009.02.026

Kasumovic, M. M., Elias, D. O., Sivalinghem, S., Mason, A. C., & Andrade, M. C. B. (2010). Examination of prior contest experience and the retention of winner and loser effects. Behavioral Ecology : Official Journal of the International Society for Behavioral Ecology, 21(2), 404–409. http://doi.org/10.1093/beheco/arp204

Kasumovic, M. M., Mason, A. C., Andrade, M. C. B., & Elias, D. O. (2011). The relative importance of RHP and resource quality in contests with ownership asymmetries. Behavioral Ecology, 22(1), 39–45. http://doi.org/10.1093/beheco/arq161

Kokko, H., Jennions, M., & Brooks, R. (2006). Unifying and testing models of sexual selection. Annual Review of Ecology, Evolution, and Systematics, 37, 43–66. http://doi.org/10.1146/annurev.ecolsys.37.091305.110259

80

Komdeur, J. (2001). Mate guarding in the Seychelles warbler is energetically costly and adjusted to paternity risk. Proceedings. Biological Sciences / The Royal Society, 268(1481), 2103–2111. http://doi.org/10.1098/rspb.2001.1750

Kotiaho, J. S., Alatalo, R. V., Mappes, J., & Parri, S. (1999). Honesty of agonistic signalling and effects of size and motivation asymmetry in contests. Acta Ethologica, 2(1), 13–21. http://doi.org/10.1007/PL00012227

Latimer, W., & Sippel, M. (1987). Acoustic cues for female choice and male competition in Tettigonia cantans. Animal Behaviour, 35(3), 887–900. http://doi.org/10.1016/S0003-3472(87)80124-0

Lawrence, W. S. (1986). Male choice and competition in Tetraopes tetraophthalmus: effects of local sex ratio variation. Behavioral Ecology and Sociobiology, 18(4), 289–296. http://doi.org/10.1007/BF00300006

Li, D., Jackson, R., & Lim, M. (2003). Influence of background and prey orientation on an ambushing predator’s decisions. Behaviour, 140(6), 739–764. http://doi.org/10.1163/156853903322370652

Lindstrom, K. (1988). Male-male competition for nest sites in the sand goby, Pomatoschistus minutus. Oikos, 53(1), 67–73. http://doi.org/10.2307/3565664

Lindström, K., & Pampoulie, C. (2005). Effects of resource holding potential and resource value on tenure at nest sites in sand gobies. Behavioral Ecology, 16(1), 70–74. http://doi.org/10.1093/beheco/arh132

Maklakov, A. a., Bilde, T., & Lubin, Y. (2004). Sexual selection for increased male body size and protandry in a spider. Animal Behaviour, 68(5), 1041–1048. http://doi.org/10.1016/j.anbehav.2004.02.010

Mathews, L. M. (2003). Tests of the mate-guarding hypothesis for social monogamy: Male snapping shrimp prefer to associate with high-value females. Behavioral Ecology, 14(1), 63–67. http://doi.org/10.1093/beheco/14.1.63

Maynard Smith, J., & Parker, G. A. (1976). The logic of asymmetric contests. Animal Behaviour, 24(1), 159–175. http://doi.org/10.1016/S0003-3472(76)80110-8

McCauley, D. E. (1982). The behavioural components of sexual selection in the milkweed beetle Tetraopes tetraophthalmus. Animal Behaviour, 30(1), 23–28. http://doi.org/10.1016/S0003-3472(82)80232-7

Mead, L. S., & Arnold, S. J. (2004). Quantitative genetic models of sexual selection. Trends in Ecology and Evolution, 19(5), 264–271. http://doi.org/10.1016/j.tree.2004.03.003

Mesterton-Gibbons, M., Marden, J. H., Dugatkin, L. a, Biology, D., & Labs, M. (1996). On wars of attrition without assessment. Journal of Theoretical Biology, 181(1), 65–83. http://doi.org/10.1006/jtbi.1996.0115

81

Morbey, Y. E. (2002). The mate-guarding behaviour of male kokanee Oncorhynchus nerka. Behaviour, 139(4), 507–528.

Neff, B. D., & Svensson, E. I. (2013). Polyandry and alternative mating tactics. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 368(1613), 20120045. http://doi.org/10.1098/rstb.2012.0045

Neumann, R., & Schneider, J. M. (2015). Differential investment and size-related mating strategies facilitate extreme size variation in contesting male spiders. Animal Behaviour, 101, 107–115. http://doi.org/10.1016/j.anbehav.2014.12.027

Nosil, P. (2002). Food fights in house crickets, Acheta domesticus, and the effects of body size and hunger level. Canadian Journal of Zoology, 80, 409–417. http://doi.org/10.1139/Z02-018

Parker, D. J., & Vahed, K. (2010). The intensity of pre- and post-copulatory mate guarding in relation to spermatophore transfer in the cricket Gryllus bimaculatus. Journal of Ethology, 28(2), 245–249. http://doi.org/10.1007/s10164-009-0176-6

Parker, G. A. (1974). Assessment strategy and the evolution of fighting behaviour. Journal of Theoretical Biology, 47(1), 223–243. http://doi.org/10.1016/0022-5193(74)90111-8

Petersson, E., Järvi, T., Olsén, H., Mayer, I., & Hedenskog, M. (1999). Male-male competition and female choice in brown trout. Animal Behaviour, 57(4), 777–783. http://doi.org/10.1006/anbe.1998.1043

Plaistow, S. J., Bollache, L., & Cezilly, F. (2003). Energetically costly precopulatory mate guarding in the amphipod Gammarus pulex: causes and consequences. Animal Behaviour, 65, 683–691. http://doi.org/10.1006/anbe.2003.2116

Poirier, N. E., Whittingham, L. a., & Dunn, P. O. (2004). Males achieve greater reproductive success through multiple broods than through extrapair mating in house wrens. Animal Behaviour, 67(6), 1109–1116. http://doi.org/10.1016/j.anbehav.2003.06.020

Polak, M. (1994). Large size advantage and assessment of resource holding potential in male Polistes fuscatus. http://doi.org/10.1006/anbe.1994.1355

Prenter, J., Elwood, R. W., & Montgomery, I. W. (2003). Mate guarding, competition and variation in size in male orb-web spiders, Metellina segmentata: a field experiment. Animal Behaviour, 66(6), 1053–1058. http://doi.org/10.1006/anbe.2003.2266

Prenter, J., Elwood, R. W., & Taylor, P. W. (2006). Self-assessment by males during energetically costly contests over precopula females in amphipods. Animal Behaviour, 72(4), 861–868. http://doi.org/10.1016/j.anbehav.2006.01.023

Reichert, M. S., & Gerhardt, H. C. (2011). The role of body size on the outcome, escalation and duration of contests in the grey treefrog, Hyla versicolor. Animal Behaviour, 82(6), 1357–1366. http://doi.org/10.1016/j.anbehav.2011.09.019

82

Riechert, S. E. (1979). Games spiders play: II. Resource assessment strategies. Behavioral Ecology and Sociobiology, 6(2), 121–128.

Ritschard, M., Riebel, K., & Brumm, H. (2010). Female zebra finches prefer high-amplitude song. Animal Behaviour, 79(4), 877–883. http://doi.org/10.1016/j.anbehav.2009.12.038

Schneider, J. M. (1997). Timing of maturation and the mating system of the spider, Stegodyphus lineatus (Eresidae): how important is body size? Biological Journal of the Linnean Society, 60, 517–525.

Schneider, Rasband, & Eliceiri. (2012). NIH Image to ImageJ: 25 years of image analysis. Nature Methods, 9(7), 671–675. http://doi.org/10.1038/nmeth.2089

Schubert, M., Schradin, C., Rödel, H. G., Pillay, N., & Ribble, D. O. (2009). Male mate guarding in a socially monogamous mammal, the round-eared sengi: On costs and trade-offs. Behavioral Ecology and Sociobiology, 64(2), 257–264. http://doi.org/10.1007/s00265-009-0842-2

Sigurjónsdóttir, H., & Parker, G. A. (1981). Dung fly struggles: Evidence for assessment strategy. Behavioral Ecology and Sociobiology, 8(3), 219–230. http://doi.org/10.1007/BF00299834

Sih, A., Lauer, M., & Krupa, J. J. (2002). Path analysis and the relative importance of male-female conflict, female choice and male-male competition in water striders, 63, 1079–1089. http://doi.org/10.1006/anbe.2002.2002

Simmons, L. W. (1986). Inter-male competition and mating success in the field cricket, Gryllus bimaculatus (de Geer). Animal Behaviour, 34(2), 567–579. http://doi.org/10.1016/S0003-3472(86)80126-9

Sivalinghem, S., Kasumovic, M. M., Mason, A. C., Andrade, M. C. B., & Elias, D. O. (2010). Vibratory communication in the jumping spider Phidippus clarus: polyandry, male courtship signals, and mating success. Behavioral Ecology, 21(6), 1308–1314. http://doi.org/10.1093/beheco/arq150

Sparkes, T. C., Keogh, D. P., & Pary, R. a. (1996). Energetic costs of mate guarding behavior in male stream-dwelling isopods. Oecologia, 106(2), 166–171. http://doi.org/10.1007/BF00328595

Suter, R. B., & Keiley, M. (1984). Agonistic interactions between male pyramila (Araneae, Linyphiidae). Behavioral Ecology and Sociobiology, 15(1), 1–7.

Tachon, G., Murray, a M., Gray, D. a, & Cade, W. H. (1999). Agonistic displays and the benefits of fighting in the field cricket, Gryllus bimaculatus. Journal of Insect Behavior, 12(4), 533–543. Retrieved from <Go to ISI>://000083375600011

Taylor, P. W., & Elwood, R. W. (2003). The mismeasure of animal contests. Animal Behaviour, 65, 1195–1202. http://doi.org/10.1006/anbe.2003.2169

Tedore, C., & Johnsen, S. (2014). Visual mutual assessment of size in male Lyssomanes viridis jumping spider contests. Behavioral Ecology, 26(2), 510–518. http://doi.org/10.1093/beheco/aru222

83

Turner, G. F., & Huntingford, F. A. (1986). A problem for game theory analysis: assessment and intention in male mouthbrooder contests. Animal Behaviour, 34(4), 961–970. http://doi.org/10.1016/S0003-3472(86)80155-5

Uhl, G., Schmitt, S., Schäfer, M. a., & Blanckenhorn, W. (2004). Food and sex-specific growth strategies in a spider. Evolutionary Ecology Research, 6(4), 523–540.

Van Dyk, D. a., Taylor, a. J., & Evans, C. S. (2007). Assessment of repeated displays: a test of possible mechanisms. Journal of Experimental Biology, 210(17), 3027–3035. http://doi.org/10.1242/jeb.007492

Vehrencamp, S. L. (2000). Handicap, index, and conventional signal elements of bird song. In Y. Espmark, T. Amundsen, & G. Rosenqvist (Eds.), Animal Signals: Signalling and Signal Design in Animal Communication (pp. 277–300). Trondheim, Norway: Tapir Academic Press.

Wada, S., Tanaka, K., & Goshima, S. (1999). Precopulatory mate guarding in the hermit crab Pagurus middendorffii (Brandt) (Decapoda: Paguridae): Effects of population parameters on male guarding duration. Journal of Experimental Marine Biology and Ecology, 239(2), 289–298. http://doi.org/10.1016/S0022-0981(99)00045-3

Wagner, W. E. (1989). Fighting, assessment, and frequency alteration in Blanchard’s cricket frog. Behavioral Ecology and Sociobiology, 25(6), 429–436. http://doi.org/10.1007/BF00300189

Ward, P. I. (1983). Advantages and a disadvantage of large size for male Gammarus pulex (Crustacea: Amphipoda). Behavioral Ecology and Sociobiology, 14(1), 69–76. http://doi.org/10.1007/BF00366658

Ward, P. I. (1988). Sexual selection, natural selection, and body size in Gammarus pulex (Amphipoda). The American Naturalist, 131(3), 348–359. http://doi.org/10.1086/521238

Watson, P. J. (1990). Female-enhanced male competition determines the first mate and principal sire in the spider Linyphia litigiosa (Linyphiidae). Behavioral Ecology and Sociobiology, 26(2), 77–90. http://doi.org/10.1007/BF00171577

Wedell, N., Gage, M. J. G., & Parker, G. A. (2002). Sperm competition, male prudence and sperm-limited females. Trends in Ecology and Evolution, 17(7), 313–320. http://doi.org/10.1016/S0169-5347(02)02533-8

Wells, M. S. (1988). Effects of body size and resource value on fighting behaviour in a jumping spider. Animal Behaviour, 36(2), 321–326. http://doi.org/10.1016/S0003-3472(88)80001-0

Wilcox, R. S. (1984). Male copulatory guarding enhances female foraging in a water strider. Behavioral Ecology and Sociobiology, 15(3), 171–174. http://doi.org/10.1007/BF00292971

Wiley, R. (1994). The evolution of communication: information and manipulation. In L. Real (Ed.), Behavioural mechanisms in evolutionary ecology (pp. 157–184). Chicago: University of Chicago Press.

84

Wong, B. B. M., & Candolin, U. (2005). How is female mate choice affected by male competition? Biological Reviews of the Cambridge Philosophical Society, 80(4), 559–571. http://doi.org/10.1017/S1464793105006809

Yamamura, N. (1987). A model on correlation between precopulatory guarding and short receptivity to copulation. Journal of Theoretical Biology, 127(2), 171–180. http://doi.org/10.1016/S0022-5193(87)80128-5