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

Sexual vs. Asexual Reproduction

Sexual male gamete + female gamete = zygote

haploid sperm haploid egg diploid offspring

Meiosis - recombination leads to genetically variable gametes

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

Sexual vs. Asexual Reproduction

Figure 7-1 Pough et al.

2001

No recombination

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.

R. lessonae R. ribidunda

R. esculenta

RL, RLL, RRL

femalemale

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

Parthenogenesis

• When females reproduce without the involvement of males or sperm

• Offspring “clones” of their mother• Occurs in 7 lizard clades & 2 snake clades

Reproduction (neuronal, hormonal, behavioral)

Figure 7-3 Pough et al.

2001

light, heat, moisture

space, food, habitatpop. density, hierarchy

gonadotropin releasing hormone

estrogen testosterone

Reproduction (patterns)

Figure 7-4 Pough et al.

2001Timing - behavior - physiology

Temperate vs. Tropical ?

Sperm Storage?

Most Common?

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

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)

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

Pough et al. 2001

Pough et al. 2001

TSD

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.

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)

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

Rana berlandieri, Big Bend N.P., Texas

Pough et al. 2001

Pough et al. 2001

Salamanders

Pough et al. 2001

Anurans

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

Stebbins and Cohen, 1995

Anuran metamorphosis

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

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

Heterochrony - common evolutionary tool

rate offset onset

e.g., Ambystoma

A. tigrinum

A. mexicanum

Figure 7-11 Pough et al.

2001

(obligate vs. facultative)

Ambystoma mexicanum (paedomorphic)

Ambystoma tigrinum (larval)

Ambystoma tigrinum (adult)

Pough et al. 2001

Pough et al. 2001

paedomorphosis

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

Pough et al. 2001

Male Parental Care in Eleutherodactylus coqui

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

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

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?

Uta

Rana cascadae

Xenosaurus

Mating Systems and Sexual Selection

Sexual Dimorphism

African reedfrog, Hyperolius argus

veiled chameleon

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

Mating Systems and Sexual Selection

Sexual Selection

Darwin 1871 as cited in Pough et al. 2001

male

male

male

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

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

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?

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

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

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

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

Rana sylvatica

Bufo bufo, Scaphiopus

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

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…

Male

Male

Female

Female

Explosive

1980

1981

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

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

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

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

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

• Chorus = anuran males calling from particular perches

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

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

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

Some males mate many times Many males don’t mate at all

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

Sacrifice energy reserves and foraging opportunities

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

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

Pough et al. 2001

Male

Males wrestling

Female Amplexus

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

Alternative Mating Tactics

Small males more likely to behave as satellites

Small satellites

density and satellites

Mating Systems and Sexual Selection

Sperm Competition - amount - vigor - longevity

Male vs. Female size - sexual selection - clutch size - ecological roles (diet)

Uta stansburiana

Atelopus