Reptile Reproduction pt. 2

Eggshells of viviparous species are

extremely thin

(Vascularized tissues of the uterine wall and chorioallantoic membrane)

gas exchange occurs where? (in the egg)

Chorioallantoic placenta

the yolk sac placenta is unique to

squamates

(Implicated in nutrient secretion by the uterus and nutrient absorption by embryonic tissues)

placentotrophy characteristics

Viviparous squamates

Nutrients are transferred to the embryo from the mother

why are squamates the only viviparous reptiles?

Predisposed for viviparity because development is initiated at fertilization, and by the time of oviposition embryos have reached limb bud stages

(in other reptiles, normal embryonic development proceeds only after the eggs are deposited)

what is the nature of transition between oviparity and viviparity

• Relatively long periods of egg retention

• Relatively short incubation periods

• Relatively thin eggshells

• The ability to extend egg retention without impairing developmen

what environmental conditions favor the evolution of viviaparity

• Associated with cold climates and evolved there

• Not restricted to cold climates

parental care benefits

increased survival of young

parental care costs

• investment of time and energy

• reduced survival

• reduced future reproductive output

very little snakes exhibit what?

parental care

the most common type of parental care exhibited by lizards is

egg attendance

A few species of large varanids use

termites to babysit their eggs

male reproductive organs include

hemipenes

spermatophores

female reproductive organs include

oogenesis

cleavage (embryonic development)

[hatching] Retraction of the amnion detaches the chorioallantois from the surface of the eggshell and

pulls it after the amnion

[hatching] as a result, all the extraembryonic membranes are gathered together with the

amnion forming a sleeve over the yolk sac

[hatching] Muscular contractions of the amnion push the yolk sac and the inner allantoic membrane into

the abdominal cavity

The basic pattern of development is directed by a common set of what genes?

HOX genes

phenotypic plasticity

The capacity for a genotype to express more than one phenotype depending on

environmental conditions

reproductive cycles

 Gonadal maturation

 Mating

 Fertilization

 Embryogenesis

 Hatching or Birth

 Parental Care

types of gonadal maturation

spermatogenesis, oogenesis, and vitellogenesis

Associated (prenuptial) gonadal cycle characterisitics

• Fertilization occurs shortly after mating

• Crocodylians and most lizards

• Typical of tropical and subtropical latitudes

Disassociated (postnuptial) gonadal cycle characteristics

• Fertilization occurs after a period of sperm storage in the reproductive tract of males, females, or both

• Temperate-zone snakes and turtles

• Occurs occasionally in other taxa, and at tropical and subtropical latitudes as well

When the number of offspring produced per year is adjusted for

adult body size, what happens?

• Species or populations with fast life histories produce many small offspring

• Species or populations with slow life histories produce a few large offspring during a breeding season