Lecture 8 - Mating Systems

7/28/2019 Lecture 8 - Mating Systems

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MATING SYSTEMSPSYCH 118 April 30, 2013

Tuesday, April 30, 13


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BASIC MATING SYSTEMS

Keep in mind: matingsystems are an integral partof social systems, but do notdefine them

Monogamy (copulation withonly one partner) is NOTpair-bonding



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BASIC MATING SYSTEMS



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MONOGAMYMating with only one individual during a specific breeding season.

Serial monogamyis common. Lifelong monogamy is rare.Tuesday, April 30, 13


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MONOGAMYExample: Oldfield mice



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FOLTZ

Studied 500 oldfield mouse burrows, and genetically tested178 of the families captured.

90% of offspring in burrows were sired by the resident male

Behavioral observations showed that F stayed with the same

M across mating seasons...

...13% of F had no resident male AND more likely to switchmates across breeding seasons...



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MONOGAMY AND FITNESS

Presumablystrong fitnessconsequences to matechoice

Ryan & Altmann (2001)mate choice experiments onoldfield mice



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PROXIMATE UNDERPINNINGS

OF MONOGAMY Prairie voles (Microtus

ochrogaster)

Friendly approach to astranger as a potential mate isprerequisite to forming a pair

bond

Once pair bond established,all behavior to strangers isaggressive



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PROXIMATE UNDERPINNINGS

OF MONOGAMY Aragona et al.

Injected a chemical known to stimulate pair bonding in voles, found itassociated with the rostral shell in the nucleus accumbens, specifically,activation of D1 and D2 receptors for dopamine

D2 activated = pair bond formed

D1 activated = aggression

Recently bonded M showed surge in D1 activation

Blocking D1 led to disappearance of aggression towards unknown F



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POLYGAMY

Mating with more than one individual in the course of a singlebreeding season

Polygyny: One male mating with multiple females

Polyandry: One female mating with multiple males

May be simultaneous orsequential



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POLYGAMY

Increases the variance inreproductive success for thecompeting sex

Variance for competing

polyandrous females is lessthan that for polygynousmales



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FEMALE DEFENSE POLYGYNY

Females are short-lived andhave low fecundity

Females mate shortly afterbecoming adults

Females are grouped closetogether in space



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LEKKING

Males set up and defend asmall arena, which containsno apparent resources

Females come and select amate



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LEKKING

http://youtu.be/AAXf4UMYnoI

http://youtu.be/AAXf4UMYnoIhttp://youtu.be/AAXf4UMYnoI


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FEMALE BENEFITS AND LEKS

Females appear to onlyreceive sperm from lekkingmales... so whats thebenefit?

Good genes... or...

Sexy-son hypothesis



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SEXY-SON HYPOTHESIS

Example: sandfly

(Lutzomyia longipalpi)

Jones et al.

Part 1: 5 M lek,1 virgin F chooses amate.10 times w/ same Ms,different F each.

Part 2: Took least attractive Msfrom Part 1, put them in new leks,force new set of Fs to chooseamong them.

Jones et al. then compared survivaland mating success in offspringfrom both parts:

Both had the same probability ofsurvival (does notsupport goodgenes)

When male offspring from Part 1were put on leks with offspringfrom Part 2, Part 1 males wereselected for mating more often(yes, sexy sons!)



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MALE BENEFITS AND LEKS

Benefits are HUGE (if you are chosen)

If youre not alpha, are there stillbenefits?

Petrie, Krupa & Burke (1999)

Molecular analysis of males on leks:average relateness of males on a lekwas 0.25 (half-siblings)

So even when not selected, there is anindirect fitness benefit to males tomaintain the lek



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CASE STUDY: EVOLUTION OF

POLYGYNY Acrocephaline warblers

Searcy et al. 1999

Range from monogamous topolygynous

Monogamous have higherlevel of paternal care

Habitat quality varies



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LEISLER ET AL.Monogamy usually in poor habitats (takes two to raise chicks). Monogamy

was ancestral, better environments lead to males choosing polygyny.



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POLYANDRY

Social insects

Thornhill & Alcock (1983)

Polyandry leads to reduced within-hive harmony (e.g., wasps)

So why does it sometimes occur?



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POLYANDRY

Sperm replenishment

Material benefits

Genetic benefits

Convenience



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PROMISCUOUS MATING SYSTEMSMales and females each mate with multiple partners in a single

breeding seasonTuesday, April 30, 13


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PROMISCUOUS MATING

SYSTEMS

Two main kinds:

True promiscuity: free for all!

Polygynandry: several

males form pair bonds withseveral femalessimultaneously



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PROMISCUITY AND MENSTRUATIONIncreased diversity of sperm means increased diversity of diseases...could menstruation have evolved to protect promiscuous females?



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ECOLOGY, EVOLUTION, AND

POLYGYNY

Resources limit female reproduction, not access to males

Males are limited by access to females

Using these simple rules, how does ecology inform matingsystems...



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POLYGYNY THRESHOLD

MODEL Used when males holdterritories that females may

choose to enter

Polygyny should occur inpatchy environments (variablequality)

Fitness among comparablyprovisioned monogamous andpolygynous females must beequal



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POLYGYNY THRESHOLD MODELExample: Mate choice in female lark buntings.

Pleszczynska et al.Tuesday, April 30, 13


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PTM AND HUMANS

Kipsigis tribe of Kenya

Colonial policy led to males acquiring variable qualities of land

Number of wives males obtained after resettlement was contingent upon thesize/quality of the land

There was a cost to females for polygyny (reduced number of children), sofemales preferred bachelors over married men when all else was held constant



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EXTRA-PAIR COPULATIONS

Socially monogamous

individuals often copulateoutside the pair bond

EPC for males is easy to see

(more females, moreoffspring)

Why do females do it?



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EXTRA-PAIR COPULATIONS

Fertility insurance (make sureeggs get fertilized)

Maximize genetic diversity ofoffspring

Use EPC to select males with

good genes but who will notform pair bonds

Increase amounts of directbenefits



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EXTRA-PAIR COPULATIONSExample: EPC in indigo buntings.

13% of female indigo bunting matings were EPCs, 27-42% of offspring sired by EPC males!



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SPERM COMPETITIONDirect competition between the sperm of males in the

reproductive tract of females



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SPERM COMPETITION

Quantity of semen(flooding)

Quality of sperm (speed,age)

Sperm plugs >>

Variable roles in sperm(kamikaze sperm hypothesis)



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SPERM COMPETITION IN

HUMANS Baker & Bellis

Number of sperm perejaculate should be a functionof how recently a female hasmated with other males

Hypothesis: the longer theinterval between matings, thegreater the number of sperm



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CRYPTIC FEMALE CHOICE

Ducks!

Forced copulation iscommon

Female internal reproductivetract has evolved to thwartthe efforts of unwantedmales

Lecture 8 - Mating Systems

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