While the sex of most snakes and most lizards is determined by sex chromosomes at the time of fertilization, the sex of most turtles and all species of crocodilians is determined by the environment after fertilization. The threshold temperature at which the sex ratio is even is The next phase can be either male or female, depending on the animal's position in the mound.
From Wikipedia, the free encyclopedia. PLOS One. Species in the genotypic group, like mammals and birds, have sex chromosomes, which in reptiles come in two major types.
Shine, R. The highlands are colder with a higher magnitude of annual temperature fluctuation and a shorter activity season, delaying maturity, thus GSD is favored so sex ratios are not skewed. Cuervo, W. Support Center Support Center. Search Article search Search.
In some species, including most mammals and insects, sex is determined solely by chromosomes; in other species, sex is a matter of environmental conditions. This hypothesis is supported by the persistence of TSD in certain populations of spotted skink Niveoscincus ocellatus , a small lizard in Tasmania, where it is advantageous to have females early in the season.
This model indicates that there is no genetic predisposition for the embryo of a temperature-sensitive reptile to develop as either male or female, so the early embryo does not have a "sex" until it enters the thermosensitive period of its development.
Did you know? Although few previous studies had supported the theory in reptiles, Pieau proposed TSD as an alternative to genotypic sex determination. Most turtles are subject to temperature-dependent sex determination.