sex ratio Flashcards
how is sex determined in many reptiles
by temperature
what does frequency dependent selection favour
the rarer sex since on average the rarer sex per individual has more offspring net effect is to produce equal sex ratio due to driving factor
concerns primary sex ratio (at birth not adult sex ratio)
it is independent of the breeding system (monogamy/ polygamy etc)
how does non random mating effect sex ratio
for example in instances on inbreeding females are preferred
ESS: evolutionarily stable strategy; optimum sex ratio
what is interesting about the parasitic wasp
nasonia vitripennis
lays eggs in a caterpillar, after hatching they breed straight away, if only one wasp has laid eggs in the caterpillar then leads to large amounts of inbreeding, no dispersal
wasps can control sex since males are haploids and females are diploids, so sex is controlled through fertilisation, proportion of males increases as number of wasps laying eggs in caterpillar increases.
what is the spider mite experiment
males are haploid, females are diploid
placed under different environments where increased local mate competition such as inbreeding produces fewer males
how does environmental favourability effect sr
parents should invest in females in bad environment sin
and should invest in males in a good environment
seychelles warbler; some females stay at nest and help males disperse, in good environments there was a female biased sex ratio since helpers bring many insects to nest increasing parents fitness, in bad environments there was a male biased sex ratio since helpers compete for food and reduce parents fitness, birds control sex ratio by influencing which sex chromosomes get into the egg, since the female is heterogametic (ZW)
what type of animals have sex determined by environent
crocodiles, turtles, fish, crustacea; temperature controls sex; favoured if parents do not control offspring environment
jacky lizard; short lived lizard; males are produced at an intermediate temperature whilst females are produced at extreme temperatures, this may be controlled by hormone manipulation, through this males and females were produced at varied temperatures, males had highest chance of lifetime reproductive success at intermediate temperatures, whilst females had lowest at intermediate and highest at high temperatures.
how might environment determining sex negatively effect an animal
sea turtle population in great barrier reef; sex depends on sand temp, high temperatures produce females and low males, however due to global warming, in north barrier reef where it is warmer there is 99% female offspring however in the south there is 67%, line between males and females; 29.3 degrees C
what is the difference between nuclear and cytoplasmic genes
nuclear genes are subject to meiosis and inherited from both sexes
cytoplasmic genes only transmitted by female, hences cytoplasmic genes favour female broods via; parthenogenesis, feminisation and killing males in animals and cytoplasmic male sterility in plants
what is parthenogenesis and how does it effect parasitoid wasp
an individual female will only produce female offspring;
occurs in parasitoid wasp, normally males are haploid however they produce females without fertilisation; mechanism is that unfertalised eggs undergo failure of 1st or 2nd mitotic division and becomes diploid
caused by intracellular wolbachia bacteria since they are not transmitted by males, benefits bacteria since they are transmitted to all offspring
parthenogenesis; reproduction without feritilisation
in wolbachia infected females produces all female broods, uninfected female produces even sex ratio, however males with PSR ‘B chromosome’ produce all male broods fertilised by sperm even though fertlised are normally female, all offspring become PSR, example of host coadaptation
how does feminization effect the woodlouse
in woodlice females are ZW, males ZZ
infected mothers with wolbachia produce all female broods, prevents male development by inhibiting androgenic gland and hormones for testes, inhibits male hormones, default sex is female
woodlice have 2 types of resistance to wolbachia; lowers wolbachia transmission in egg and another one prevents feminisation
in some populations the W chromosome is lost, all individuals are ZZ and sex determination is controlled by wolbachia infection
in some populations there is no W chromosome and no wolbachia infection; sex determination by f element in nuclear genome, f element is insert of 83% of wolbachia genome, acts as a neo W chromosome
how do cytoplasmic factors cause male killers
caused by cytoplasmic bacteria; produce all female brood, male eggs die, caused by variety of bacteria such as alpha proteobacteria and wolbachia in ladybirds
what is a male killing mechanism
in drosophila infected by spiroplasma
single X male has higher rate of gene expression than double X in female, the single X attracts MSL proteins (male specific lethal), the infection attacks the MSL proteins in mitosis which causes DNA damage and breaks to X chromosome which induces p53 apoptosis and embryonic death
give an example of male killer suppressors
study of hyplominas bolina, 2 seperate populations; polynesia and thailand
in polynesia female ratio was 100:1, males are ones that lack wolbachia infection
in thailand there is 1:1 ratio however both are infected with wolbachia, the thai nuclear genome suppresses wolbachia male killing
give an example of cytoplasmic male sterility
gynodioecy; hermaphrodite and female plants do not produce functional pollen
caused by mitochondrial genes, chimeric genes (recombinant), causing apoptosis of male tissues; benefit to mitochondria is to redirect resources to female function and increase seed production,
there are Rf resistance genes in nucleus which provide resistance, evolved to combat mitochondrial genes causing male sterility
