Temperature-dependent sex determination in three reptile species: the American alligator Alligator mississippiensisthe red-eared slider turtle Trachemys scripta elegansand the alligator snapping turtle Macroclemys temminckii. It is not thought that turtles can reverse their sex after this period.
In this Page. Developmental Dynamics. The results, which found evidence of TSD in four out of five species, confirmed that some vertebrate species exhibit TSD. In these reptiles, the temperature of the eggs during a certain period of development is the deciding factor in determining sex, and small changes in temperature can cause dramatic changes in the sex ratio Bull
Other work centers on a theoretical model the Charnov — Bull model  predicted that selection should favour TSD over chromosome -based systems when "the developmental environment differentially influences male versus female fitness";  this theoretical model was empirically validated thirty years later  but the generality of this hypothesis in reptiles is questioned.
The lizards were female in appearance and were capable of bearing offspring, despite having the ZZ chromosomes usually associated with male lizards. Sign Up. The turtles were incubated at temperatures that produce solely males, both sexes, and solely females. Fertility and Sterility.
It has been proposed  that temperature acts on genes coding for such steroidogenic enzymesand testing of homologous GSD pathways has provided a genic starting point. Figure In this species, individuals pile up on top of one another to form a mound Figure Sunderland MA : Sinauer Associates ;
A study found that hot temperatures altered the expression of the sex chromosomes in Australia's bearded dragon lizards. Variations on this theme also exist. By agreement with the publisher, this book is accessible by the search feature, but cannot be browsed. These chemicals block the conversion of testosterone to estradiol during development so each sex offspring can be produced at all temperatures.
Scientists are still working to understand the evolution of TSD and the implications of climate change for species that exhibit this mechanism of sex determination.