Genetic Polymorphisms in Aromatase (cyp19a1) Are Not Associated with Gonadal Phenotypes in Red-Eared Slider Turtle Hatchlings Developed at a Pivotal Temperature.

Embryonic gonad sex in many reptilian species is determined by the incubation temperature of the egg, a differentiation process known as temperature-dependent sex determination (TSD). Incubation at the pivotal temperature (PvT) results in approximately an equal number of offspring of both sexes. We investigated the potential contribution of genetic variations that drives the gonadal differentiation into testes or ovaries under this temperature in the red-eared slider turtle (Trachemys scripta). Four male and 4 female hatchlings of eggs that had been incubated at the PvT were examined for polymorphisms at an approximately 23-kb region of the aromatase (cyp19a1) gene. By aligning the red-eared slider aromatase gene to a reference genome of the western painted turtle (Chrysemys picta bellii), we discovered 22 exonic and 1,268 intronic polymorphisms. Of these, 12 (55%) exonic polymorphisms were unique to the individuals of the red-eared slider; 10 were synonymous and 2 were nonsynonymous changes. We found no pattern in these genetic variants as well as intronic variants that are consistently different between male and female hatchlings at the PvT. Overall, our study suggests that polymorphisms within the aromatase gene - at least by themselves - do not constrain the gonad sex differentiation in embryos developed at the PvT.