Transcript Lecture 2 Reproduction

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
Pough et al., 2001
- deleterious mutations
Komodo Dragon female ZW male ZZ
Hybridogenesis - e.g., Rana; female genome unchanged
Gynogenesis - e.g., Ambystoma; no genes from male
Sexual vs. Asexual Reproduction
No
recombination
Figure 7-1
Pough et al. 2001
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
male
female
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
Figure 7-3
Pough et al. 2001
Reproduction (neuronal, hormonal, behavioral)
light, heat, moisture
space, food, habitat
pop. density, hierarchy
gonadotropin releasing hormone
estrogen
testosterone
Reproduction (patterns)
Figure 7-4
Pough et al. 2001
Timing
- 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)
Egg
- ovary to oviduct
- yolk (from liver)
Amphibians (anamniotic)
Figure 7-5
Pough et al. 2001
Reptiles (amniotic egg)
- shell
- membranes
- H2O, protection
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
TSD
Pough et al. 2001
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)
Notophthalmus viridescens (Eastern Newt)
Paedomorphosis
skip the adult stage
Notophthalmus
add a juvenile eft stage
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
Salamanders
Pough et al. 2001
Anurans
Pough et al. 2001
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
Gas exchange, water, temperature
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
Birds, crocs, tuataras, some turtles - ~no water uptake
Squamates and some turtles - lots of water uptake
Heterochrony - common evolutionary tool
rate
offset
onset
e.g., Ambystoma
A. mexicanum
A. tigrinum
(obligate vs.
facultative)
Figure 7-11
Pough et al. 2001
Ambystoma mexicanum
(paedomorphic)
Ambystoma tigrinum
(larval)
Ambystoma tigrinum
(adult)
Pough et al. 2001
paedomorphosis
Pough et al. 2001
Parental Care
costs vs. benefits to parents
Amphibs
caecilians
- egg attendance (all)
salamanders - egg attendance (20%)
anurans
- diverse (10%)
- egg attendance, transport
- egg and tadpole development (outside oviduct)
- tadpole guarding, transport
- tadpole feeding
Pipa pipa
Rheobatrachus vitellinus
Male Parental Care in Eleutherodactylus coqui
Pough et al. 2001
Parental Care
Reptiles
turtles
crocs
squamates
- rare, ineffective?
- all, vocalizations
- some
Python regius
-
nest defense
egg attendance (several snakes)
egg brooding (e.g., Pythons)
hatchling attendance
(a few viviparous species,
e.g., some Crotalus)
Viviparity (Parental Care)
= retention of embryos in oviduct until
development complete
Found 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
- assoc. with cold (in squamates)
- trade-offs
- lecithotrophy
- placentotrophy
- matrotrophy
Fig. 17-13
Stebbins and Cohen, 1995
Life History
Figure 7-20
Pough et al. 2001
Reproductive Effort
(RCM, relative clutch mass)
- current vs. future
- current vs. survival
Energy per Progeny
1 vs. 50,000 eggs/clutch
egg size optimized? constrained?
parental care and viviparity => few large
Trade-offs?
Xenosaurus
Rana cascadae
Uta
Mating Systems and Sexual Selection
Sexual Dimorphism
veiled chameleon
African reedfrog, Hyperolius argus
Mating Systems and Sexual Selection
Sexual Selection
-Directional selection that acts on genetically variable
phenotypic traits that affect the reproductive success
of the individuals of a particular sex
- secondary sexual characteristics
Coloration
Size
Crests
-Usually in the male
b/c females are the limiting resource
Mating Systems and Sexual Selection
Sexual Selection
male
Darwin 1871 as cited in
Pough et al. 2001
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 scramble
2. Few dispersed = males go searching
3. Intermediate = many options…
- Mate guarding
- Signalling to attract
- dispersed
- lekking
- Defend territories
- food resources
- nesting sites
Grade into each other
Intraspecific variation
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
-Spatial aggregation
some Thamnophis,
Natrix (spring at den)
Males outnumber females
(e.g., 10-1)
male-male competition
Pough et al. 2001
including
Sexual Interference
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
Thamnophis sirtalis parietalis – males swamp the few females that emerge…
High numbers of male garter snakes die soon after emerging
from hibernation because they are attacked by crows. Shemales at the center of a mating ball, however, are less
exposed to predators – also remain warmer…
Explosive
Male
1980
Female
1981
Male
Female
Mating Systems and Sexual Selection
Mating Systems
Mate Searching
- some salamanders
- common in reptiles
- turtles and tortoises
- snakes
tend to be solitary
follow pheromones
Thamnophis sirtalis
- populations may vary
density
fewer, widely dispersed = more search time and
more waiting
- widely foraging lizards
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 male
Atelopus (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 Selection
Mating Systems
Leks= 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 cristatus
Marine iguana
• Chorus = anuran males calling from
particular perches
Mating Systems and Sexual Selection
Mating Systems
Resource 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
Male size and vigor may be correlated
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)
Mating Systems and Sexual Selection
Mating Systems
Resource 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
e.g. Amount of time male anuran spends in chorus
positively correlated with mating success
Sacrifice energy reserves
and foraging opportunities
Salamander lesson:
Explosive aggregations (~Ambystoma)
males deposit many, many spermatophores
most not picked up by a female
Courtship (~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
~
Larger body size
Also important for
territorial species
(indirectly)
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
Male-male assessment
- size
- color
- repeat encounters
Pough et al. 2001
Male
Males wrestling
Female
Pough et al. 2001
Amplexus
Mating Systems and Sexual Selection
Alternative Mating Tactics
- Sneaking/Satellite
- Female Mimicry
- Sexual Interference
Uta stansburiana
orange super male
blue mate guarder
yellow sneaker
Pough et al. 2001
Small satellites
Alternative Mating Tactics
Small males more likely
to behave as 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