Hormone levels in yolk decline throughout development in the red-eared slider turtle (Trachemys scripta elegans)

This study investigates the potential effects of maternally derived hormones present in the yolk of reptile eggs. Specifically, we ask when are these hormones utilized by developing red-eared slider turtles (Trachemys scripta elegans), a species with temperature-dependent sex determination (TSD). Eggs were incubated at 27 degrees C, a male-producing temperature, and at 31 degrees C, a female-producing temperature. Concentrations of progesterone, testosterone, and 17beta-estradiol were measured at four points during development: at oviposition, at the start of the temperature sensitive period (TSP), at the end of the TSP, and at hatching. No effects of incubation temperature on yolk hormone concentrations were detected. The highest concentrations of all three hormones were measured at oviposition. Hormone-specific patterns of decline occurred throughout development. Each hormone declined between oviposition and the early TSP. Although estradiol was present in detectable quantities at oviposition, it was virtually undetectable by the early TSP. Testosterone showed no further decline after the early TSP. Progesterone continued to decline between the early and post-TSP. These results demonstrate that maternally derived yolk hormones decline at different rates. Alternative explanations for the disappearance of these yolk hormones are presented.