The mechanism that final sex-determination is done by not chromosomes but interaction with temperatures that is exposed during differentiation into an embryo, a larva or an adult is called TSD ( temperature-dependent sex determination). TSD is found in lizards, crocodiles, turtles, amphibians, and fishes. This mechanism is thought to have some sort of adaptive significances, because this mechanism remains until the present age, and also has hypothesizes. One of them is “If there is the temperature-dependent in male and female fitness, TSD is probability of adaptive mechanism”.
In this announcement, we assume that male’s survival rate doesn’t depend on incubation temperature, female’s survival rate depends on incubation temperature (monotonic increase), and individuals in nature have a variety of threshold temperatures (v). An embryo becomes male in incubation temperature < v and female in incubation temperature > v.
We construct a model under the assumption. I investigate that female ’s survival rate and variance of temperature in habitat affect expected value of threshold temperature (sex ratio of children) by natural selection.