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Reproduction
Mating - physiological - morphological - behavioral/social events
Tied to life history (annual and life cycle)
Interesting variations - asexual reproduction - sperm storage - viviparity - parental care - sex determination - heterochrony
Pough et al., 2001
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Sexual vs. Asexual Reproduction
Sexual male gamete + female gamete = zygote
haploid sperm haploid egg diploid offspring
Meiosis - recombination leads to genetically variable gametes
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Sexual vs. Asexual Reproduction
Asexual ~ hybrid origin ~ female populations ~ clonal reproduction
Parthenogenesis - 30 species of squamate - many Cnemidophorus (1/3)
- pseudocopulation - deleterious mutationsKomodo Dragon female ZW male ZZ
Hybridogenesis - e.g., Rana; female genome unchangedGynogenesis - e.g., Ambystoma; no genes from male
Pough et al., 2001
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Sexual vs. Asexual Reproduction
Figure 7-1 Pough et al.
2001
No recombination
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Hybridogenesis
When females produced via hybridization between 2 closely related species produce only female offspring (all genetically identical to the mother)
This mode marks hybrids between two parental species (A,B) who are able to reproduce by backcrossing with one of the parents.
These hybrid normally contain two chromosome sets (AB, one from each parent species) in their body cells, but in the gonads the chromosome set of one parent is lost, so that only one set remains (A or B), with A in their gonads, hybrids can backcross with B and vice versa.
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R. lessonae R. ribidunda
R. esculenta
RL, RLL, RRL
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femalemale
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Gynogenesis
• Egg development activated by a spermatozoon, but to which the male gamete contributes no genetic material
• Ambystoma laterale-jeffersonianum complex: females use sperm from a sympatric, diploid male to initiate the development of the eggs without incorporating the male genome
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Parthenogenesis
• When females reproduce without the involvement of males or sperm
• Offspring “clones” of their mother• Occurs in 7 lizard clades & 2 snake clades
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Reproduction (neuronal, hormonal, behavioral)
Figure 7-3 Pough et al.
2001
light, heat, moisture
space, food, habitatpop. density, hierarchy
gonadotropin releasing hormone
estrogen testosterone
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Reproduction (patterns)
Figure 7-4 Pough et al.
2001Timing - behavior - physiology
Temperate vs. Tropical ?
Sperm Storage?
Most Common?
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Reproduction (fertilization)
Amphibians External = ancestral
Internal: Caecilians - phallodeum (almost all) Salamanders - spermatophore (most) Anurans - ‘tail’ or cloacal apposition (quite rare)
Reptiles Internal
Sphenodontids - cloacal apposition Turtles and Crocs - penis Squamates - hemipenes
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Reproduction (gametes)
Figure 7-5 Pough et al.
2001
Reptiles (amniotic egg)
- shell - membranes - H2O, protection
Amphibians (anamniotic)
Egg - ovary to oviduct - yolk (from liver)
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Reproduction (nutrition and sex determination)
oviparous <--> viviparous (more when talk about parental care)
Lecithotrophic - rely on yolk Placentotrophic - additional nutrients from mother
GSD - Genotypic Sex Determination heterogamety, variable in herps
TSD - Temp.-dependent Sex Determination many reptiles not known to occur in amphibs
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Pough et al. 2001
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Pough et al. 2001
TSD
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TSD
- During middle third or half of development - Gene activity temp. dependent? - alter testosterone (in yolk from mother) - Females:
aromatase produced converts testosterone to estradiol (estrogen) stimulates creation of ovaries and more estrogen secondary sexual characteristics etc.
-Males: 5alpha-reductase produced converts testosterone to dihydrotestosterone stimulates creation of testes and more androgens secondary sexual characteristics etc.
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Amphibian Life Cycles and Reproductive Modes
Common: egg --> larva --> adult
Direct Development skip the larval
stage (e.g.,
Eleutherodactylus) Paedomorphosis
skip the adult stageNotophthalmus
add a juvenile eft stage
Notophthalmus viridescens (Eastern Newt)
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Amphibian Life Cycles and Reproductive Modes
Caecilians - mostly oviparous --> larvae or direct
Salamanders - oviparous (pond, stream, nonaquatic)
- direct in Plethodontids Anurans - oviparous ancestrally
- eggs variable, correlated with habitat
(clumps, strings, foam, etc.) - trend to move on to land
small pools seed husks bromeliads, etc.
- multiple evol. of direct development
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Rana berlandieri, Big Bend N.P., Texas
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Pough et al. 2001
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Pough et al. 2001
Salamanders
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Pough et al. 2001
Anurans
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Amphibian Larval Development and Metamorphosis
Caecilians - basically small adults with gills
- lose eyes, gain tentacles Salamanders - small adults with gills, larval dentition
- always carnivorous
Anurans - variable - days to years as tadpole
- metamorphosis is dramatic (suspension feeding to carnivore)
adult gut and stomach develop jaws, teeth, tongue eyelids, lungs, ossification
Dendrobates auratus
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Stebbins and Cohen, 1995
Anuran metamorphosis
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Metamorphosis
• Density dependent variation – when growth conditions are poor, larvae should metamorphose near the minimum size; when conditions are good, larvae should metamorphose near the maximum size
• Plasticity in larval growth• paedomorphosis
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Reptilian Egg and Embryonic Development
Oviparity or viviparity - no larval stage
Shell - calcium carbonate layer, fibrous inner layer
- thin to thick (vary the outer mineral layer)- thinnest in viviparous species
~ thin if take water from environment
Gas exchange, water, temperature
Birds, crocs, tuataras, some turtles - ~no water uptakeSquamates and some turtles - lots of water uptake
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Heterochrony - common evolutionary tool
rate offset onset
e.g., Ambystoma
A. tigrinum
A. mexicanum
Figure 7-11 Pough et al.
2001
(obligate vs. facultative)
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Ambystoma mexicanum (paedomorphic)
Ambystoma tigrinum (larval)
Ambystoma tigrinum (adult)
Pough et al. 2001
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Pough et al. 2001
paedomorphosis
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Parental Care costs vs. benefits to parentsAmphibs
caecilians - egg attendance (all) salamanders - egg attendance
(20%) anurans - diverse (10%)- egg attendance, transport
Rheobatrachus vitellinus
- egg and tadpole development (outside oviduct)- tadpole guarding, transport - tadpole feeding
Pipa pipa
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Pough et al. 2001
Male Parental Care in Eleutherodactylus coqui
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Parental Care
Reptiles turtles - rare, ineffective? crocs - all, vocalizations squamates - some
- nest defense- egg attendance (several snakes)- egg brooding (e.g., Pythons)
- hatchling attendance (a few viviparous species, e.g., some Crotalus)
Python regius
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Viviparity (Parental Care) = retention of embryos in oviduct until
development completeFound in - some caecilians (~20%) - a few frogs - a few salamanders (some Salamandrids) - some squamates (~20%); no turtles, crocs
- reduced shell thickness - increased gas exchange - maintenance of hormone levels
- lecithotrophy - placentotrophy - matrotrophy
- assoc. with cold (in squamates) - trade-offs
Fig. 17-13 Stebbins and Cohen, 1995
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Life History
Reproductive Effort (RCM, relative clutch mass) - current vs. future - current vs. survival
Energy per Progeny 1 vs. 50,000 eggs/clutch
Figure 7-20 Pough et al.
2001
parental care and viviparity => few large
egg size optimized? constrained?
Trade-offs?
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Uta
Rana cascadae
Xenosaurus
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Mating Systems and Sexual Selection
Sexual Dimorphism
African reedfrog, Hyperolius argus
veiled chameleon
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Mating Systems and Sexual Selection
Sexual Selection
- secondary sexual characteristics
-Directional selection that acts on genetically variable phenotypic traits that affect the reproductive success of the individuals of a particular sex
Coloration Size Crests
-Usually in the male b/c females are the limiting resource
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Mating Systems and Sexual Selection
Sexual Selection
Darwin 1871 as cited in Pough et al. 2001
male
male
male
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Mating Systems and Sexual Selection
Sexual Selection
Two components:
1. Male – male competition for access to females
2. Female choice (of which male to mate with)
Pough et al. 2001
Pough et al. 2001
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Males more affected by sexual selection than females
• Females – spend energy on egg production ability
• Males – a whole lot of little cheap sperm
• Magnitude of sperm production favors fertilization of eggs from many females
• Males do not need to find quality mates, rather quantity mates
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Mating Systems and Sexual Selection
Mating Systems
Most herps polygynous
- Individual male reproductive success variable
- Some males mate with more than one female
- Many males don’t mate at all
Females Choose By?
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Why do females prefer certain phenotypic traits?
1) Direct Benefit: Certain male characters (nuptial gifts of food or defensive compounds, care provided to offspring)
2) Good genes: Male characters are "indicators" of "good genes", i.e.,
3) Sensory bias or sensory drive: some aspect of the sensory world biases females
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Natural Selection vs. Sexual Selection
• Sexual Selection and Natural Selection may actually oppose each other – Increased color/ behavior that attracts
predation– Increased cost of maintaining a territory– Heavy weaponry
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Mating Systems and Sexual Selection
Mating Systems
Behavioral tactics used by males depends on the spatial and temporal distribution of females:1. Many clumped briefly = explosive scramble2. Few dispersed = males go searching
3. Intermediate = many options…
- Mate guarding
Grade into each other Intraspecific variation
- Signalling to attract - dispersed - lekking
- Defend territories - food resources - nesting sites
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Mating Systems and Sexual Selection
Mating Systems
Explosive Mating Aggregations
- Temporary ponds Spea, Scaphiopus, ~Rana
-Flood the world with sperm-some ambystomatid salamanders and frogs
Pough et al. 2001
-Spatial aggregationsome Thamnophis, Natrix (spring at
den)Males outnumber females (e.g., 10-1) male-male competition
Sexual Interferenceincluding
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Rana sylvatica
Bufo bufo, Scaphiopus
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Sperm Competition
• Multiple paternity– the red-eyed tree frog
(Agalychnis callidryas), the Australian frog (Crinia georgiana), and the common frog (Rana temporaria).
• Genetically superior sperm more likely to survive (better to mate with several males)
Chiromantis xeramplina – African gray treefrog
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High numbers of male garter snakes die soon after emerging from hibernation because they are attacked by crows. She-males at the center of a mating ball, however, are less exposed to predators – also remain warmer…
Thamnophis sirtalis parietalis – males swamp the few females that emerge…
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Male
Male
Female
Female
Explosive
1980
1981
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Mating Systems and Sexual Selection
Mating Systems
Mate Searching
- some salamanders
- common in reptiles
- turtles and tortoises - snakes tend to be solitary follow pheromones
- populations may vary density fewer, widely dispersed = more search time and
more waiting - widely foraging lizards
Thamnophis sirtalis
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Mating Systems and Sexual Selection
Mating Systems
Mate Searching
- Crotalus viridis
Overwinter in communal dens Disperse in spring and forage widely Males search for females in midsummer Most males don’t find a female Long term strategy
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Mating Systems and Sexual Selection
Mating Systems
Mate Guarding: If searching for mate is costly, then it may be worthwhile to invest energy in guarding her from other males
- amplexus in anurans and salamanders
salamander - male may physically carry away female- male with enlarged teeth used to deter other maleAtelopus (Bufonidae)-male may amplex weeks/months before breeding season- costs to female and male
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Mating Systems and Sexual Selection
Mating Systems
Mate Guarding
Gopherus agassizii - Male searches for female - Stays with her many days - Wards off other males
use of gular Territorial lizards - male will guard female - forfeit other females photos by Roger A. Repp
Tiliqua rogusa - multi-year pair bonds
Some Snakes - often wrestling contests - ‘topping’
Crotalus atrox
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Mating Systems and Sexual SelectionMating SystemsLeks= aggregations of males that gather in sites, defend small territories, and display for females
Females choose males based on their traits -color, size, vigor, display structures
Triturus cristatusMarine iguana
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• Chorus = anuran males calling from particular perches
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Mating Systems and Sexual SelectionMating SystemsResource Defense
Resources attractive to females - oviposition sites - feeding areas
Male mating success depends more on resource quality than on the characteristics of the male per se
Not common in salamanders, but: Cryptobranchids with external fertilization - defend territories with nesting sites
Red-backed salamanders (Plethodon cinereus) - female judges territory quality based on male feces (termites better than ants)
Male size and vigor may be correlated
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Mating Systems and Sexual SelectionMating SystemsResource Defense
Resources attractive to females - oviposition sites - feeding areas
Rana clamitans (green frogs) Rana catesbeiana (bullfrog)
Territories guarded for ~2 months (during breeding season) appropriate oviposition sites (water temperature)
Territorial Lizards Male with large quality territory likely to encompass many female territories
Pough et al. 2001
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Mating Systems and Sexual Selection
Male Reproductive Success
Some males mate many times Many males don’t mate at all
Variance in reproductive success leads to strong sexual selection and sexual dimorphism
- Search time - Competition - Attractiveness - Handling time - Parental care
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Some males mate many times Many males don’t mate at all
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Mating Systems and Sexual Selection
Male Persistence and Allocation of Resources
Stamina
Salamander lesson:
e.g. Amount of time male anuran spends in chorus positively correlated with mating successSacrifice energy
reserves and foraging opportunities
Explosive aggregations (~Ambystoma) males deposit many, many
spermatophores most not picked up by a femaleCourtship (~Salamandridae, Plethodontidae) males court extensively, deposit few spermatophores – female
picks up
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Sacrifice energy reserves and foraging opportunities
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Mating Systems and Sexual Selection
Male Competitive Ability
- explosive breeding aggregations - mate searching - mate guarding
Also important for territorial species (indirectly)
~ Larger body size
Pough et al. 2001
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Mating Systems and Sexual Selection
Male Competitive Ability/ Sexual Dimorphism
- Frog fangs - Frog wrestling - Frog trunk muscles - Newt tail fins - Lizard biting - Snake wrestling
Pough et al. 2001
Male-male assessment - size - color - repeat encounters
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Pough et al. 2001
Male
Males wrestling
Female Amplexus
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Mating Systems and Sexual Selection
Alternative Mating Tactics
- Sneaking/Satellite - Female Mimicry - Sexual Interference
Pough et al. 2001
Uta stansburiana orange super male blue mate guarder yellow sneaker
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Alternative Mating Tactics
Small males more likely to behave as satellites
Small satellites
density and satellites
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Mating Systems and Sexual Selection
Sperm Competition - amount - vigor - longevity
Male vs. Female size - sexual selection - clutch size - ecological roles (diet)
Uta stansburiana
Atelopus