If such a snail is removed from its attachment, it will become female. Genetics Selection Evolution. Sex-determining mechanisms in reptiles are broadly divided into two main categories: genotypic sex determination GSD and temperature-dependent sex determination TSD.
Estrogen can override temperature and induce ovarian differentiation even at masculinizing temperatures. In researchers established the existence of genotypic sex determination among turtlesa result that weakened support for TSD in reptiles and in vertebrates.
Genetics Selection Evolution. 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. Washington: Smithsonian Books, Journal of Evolutionary Biology.
In Emys, the last third of development appears to be the most critical for sex determination. Adams The consequences of TSD on fitness, or reproductive success, are largely unknown. Non-genetic sex determination occurs when the sex of an organism can be altered during a sensitive period of development due to external factors such as temperature, humidity, or social interactions.
Also, experiments conducted at the pivotal temperature, where temperature is equivocal in its influence, have demonstrated an underlying genetic predisposition to be one sex or the other. Views Read Edit View history.
The evolutionary advantages and disadvantages of temperature-dependent sex determination are discussed in Chapter Recent studies Bergeron et al.
Cite this Page Gilbert SF. Turtles of the World. More examples of context-dependent sex determination will be studied in Chapter Sunderland MA : Sinauer Associates; These chemicals block the conversion of testosterone to estradiol during development so each sex offspring can be produced at all temperatures.
Very near or at the pivotal temperature of sex determination, mixed sex ratios and more rarely intersex individuals.