ESD and Asexual Reproduction

sex determination in embryos

genetic

• at fertilization

temperature dependent

• during early development

sex determination

genetic is ancestral

one sex is heterogametic (2 different sex chromosomes)

one sex is homogametic (2 same sex chromosomes)

affects expression of specific genes

• affects production of specific proteins and hormones

only genetic in amphibians and mammals

ESD in crocs

both in lizards, snakes, turtles

temperature dependent determination

3 patterns

• males from cooler nests (turtles)

• females from cooler nests (some lepidosaurs; tuataras)

• females from coolest and warmest nests, males from intermediate (turtles, crocs, lizards)

  • some have few males produced at all temps

ESD & production of both sexes

species vary in range of temps where both sexes produced

always a somewhat narrow range

ESD mechanism

temperature sensitivity in embryos before gonad differentiation

temperatures lead to change in hormones

temperature dependent enzyme aromatase

ecological implications of ESD

for species with genetically determined sex, the sex ratio generally fluctuates around 1:1

with ESD potential for variance is much greater

asexual reproduction

most vertebrates reproduce sexually

some vertebrates reproduce asexually

all asexual have

• female populations

• clonal inheritance

• hybrid origin

  • high heterozygosity

3 types

asexual reproduction

parthenogenesis

clonal reproduction of females

no males, no sperm, no mating

some lizards and snakes

sometimes pseudocopulation

some diploid, some triploid

asexual reproduction

kleptogenesis

mating of male and female, sperm is either

• not incorporated

• partially incorporated

steal some male gametes some times, lose some female gametes, or keep all

ambystoma

mistakes

• new polyploids

asexual reproduction

hybridogenesis

hemiclonal

only one frog complex

need mates

• backcross to one hybrid

• no male gametes

female gemates clone that hald

depend on parent taxa