Effects of Incubation Temperatures on Sexual Differentiation in the Turtle, Chelydra serpentha

Eggs of the common snapping turtle, Chelydra serpentinu, were incubated at constant temperatures ranging from 20°C to 30°C. At hatching, the oviducts were absent or incomplete in males; the testes were differentiated. In females at hatching, the oviduct was intact but in some cases the gonad retained bisexual characteristics. Three months after hatching, the ovary was differentiated and contained follicles. Eggs incubated at 20°C and at 30°C developed into females in 100% of the cases. At 26°C. 99% of the individuals were males; at 24"C, 100% were males. More males than females developed at incubation temperatures of 22°C and 28°C. In populations of turtles, females usually outnumber males. The first and most extensive study on incidence of sex in turtles was done by Hildebrand ('29) who recorded sex in over a thousand specimens of Malaclemys hatched in pens at Beaufort, North Carolina; the ratio was 1 male to 4.4 females. In reports by Risely ('33~11, Cagle ('42, '50) and Tinkle ('611, females were usually found more frequently in nature than males. Recently, Pieau ('71, '72, '73a, b) incubated eggs of Emys orbicularis and Testudo graeca under controlled laboratory conditions and found that temperatures during incubation were determinants of sexual differentiation. Information relating sex differentiation to incubation temperature in Chelydra serpentina is presented here. These observations on Chelydra confirm in general the findings of Pieau.