Reptile Reproudction pt. 1

the ancestral conditions for reptiles is

temperature-dependent sex determination (TSD) (probably)

[GSD for vertebrates]

how TSD works

temperature releases sex-specific enzymes that will either turn into male or female based on the temp

TSD pattern la

males produced at cooler temperatures, females at warmer temperatures

these reptiles experience TSD pattern la

turtles

squamates

TSD pattern lb

females produced at cooler temperatures, males at warmer temperatures

these reptiles experience TSD pattern lb

tuatara

TSD pattern ll

females produced at both cooler and warmer temperatures, males at intermediate temperatures

these reptiles experience TSD pattern ll

turtles

squamata

crocodylians

The pivotal temperature

constant temperature that results in the production of equal numbers of males and females

genetic sex determination (GSD): in males, the sex-determining region is

present

(testosterone)

genetic sex determination (GSD): in females, the sex-determining region is

absent

for TSD, males produce

5a-reductase

Converts testosterone to dihydrotestosterone

Triggers differentiation into teste

for TSD, females produce

aromatase

Converts testosterone to estradiol (an estrogen)

Triggers differentiation into ovaries

GSD produces what sex ratio

1:1

TSD remains unclear in

adaptive signifigicance (relative to the sex ratio)

The Charnov–Bull model

Predicts that TSD will enhance individual fitness if:

• The fitness of sons is greatest for individuals that hatch from eggs incubated at temperatures that normally produce males

• The fitness of daughters is greatest for individuals that hatch from eggs incubated at temperatures that normally produce females

Eggs in natural nests experience

a daily variation in temperature

an ecological consequence of TSD is

climate change

how climate change affects TSD

• likely to have a negative impact on many reptiles, and species with TSD may be especially at risk

• Change may be too rapid to allow long-lived TSD species such as freshwater turtles and tuatara to avoid extinction through genetically based shifts in their thermal physiology

• TSD species may be able to avoid or reduce bias in sex ratio in response to climate change by adjusting their nesting behavior, at least in the short term

asexual reproduction is present in how many species/families?

40 species of squamates in 7 families

families include: agamid, gekkotan, lacertid, and teiid lizards

three shared features of asexual reproduction

• They originate from hybridization of two or three species

• All individuals are female

• Reproduction is via clonal inheritance

parthenogenesis does not involve

fertilization

Diploid unisexual species are the product of

hybridization between two bisexual species

Triploid unisexual species are the product of

hybridization between a diploid unisexual individual and a male of one of the parental bisexual species or of a third species

Pseudocopulation

the stimulation of sexual behavior may enhance gonadal activity (ovulation)

reptile egg shell function

Makes eggs resistant to water loss while allowing passage of respiratory gases and water vapor

the eggshell has two layers

an outer mineral layer

an underlying organic layer

the mineral layer consists of

• calcium carbonate

• Often organized into discrete shell units - represent the growth of crystals that form the outer surface of the shell

• Thin in some turtles, most squamates

the organic layer (SHELL MEMBRANE) is formed from

multiple layers of proteinaceous fibers

crocodylian shell units are what shaped?

wedge shaped

lizard shell units are what?

poorly defined; relatively thin to the mineral layer

Rigid-shelled eggs of crocodylians, tuatara, and turtles contain

all the water that the embryo will need to complete development

Flexible-shelled eggs of most squamates contain

relatively little water at oviposition- must take up water from the environment

One of the important behavioral components of successful reproduction is the selection of

a nest site where physical conditions will remain suitable during incubation

crocodylians build their nest in a

mound of decaying vegetation

most turtles and lizards build their nests in

a constructed area IN the ground

snakes build their nests where?

casually buried in debris

(Secluded in cavities in the ground or in trees)

gekkotans with rigid-shelled eggs lay their eggs where?

glued to a surface