Gilbert SF. The adaptive significance of TSD is currently not well understood. Young individuals are always male.
Another hypothesis is that aromatase activity may be regulated by Sox9. Bibcode : PLoSO 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.
This correlation is seen to hold under natural conditions as well. PLOS Biology. One of the best-studied reptiles is the European pond turtle, Emys obicularis.
Physiological and Biochemical Zoology. The thermosensitive, or temperature-sensitive, period TSP is the period during development when sex is irreversibly determined. Hormones and temperature show signs of acting in the same pathway, in that less hormone is required to produce a sexual shift as the incubation conditions near the pivotal temperature.
Views Read Edit View history. Sexual Development. As mentioned in Chapter 3, the sex of the echiuroid worm Bonellia depends on where a larva settles.