Temperature-dependent sex determination of a sea turtle, Caretta caretta, from Miyazaki, Japan

Abstract

Eggs of Caretta caretta collected from Miyazaki, Japan, were incubated at constant temperatures and a fluctuating temperature. A temperature shift experiment was also conducted. Three clutches, comprising 332 eggs in total, were used for the experiments. The mean hatching success was 0.73. The incubation period was fitted to the equation, D = 1265.56164–78.04757 T+1.25232 T² (r² = 0.951), where D is incubation duration (days) and T is the incubation temperature (°C). In all experiments, all hatchlings were clearly one sex or the other. At constant temperatures, the sex ratio (proportion of males) was 1.0 at 27.7°C, 0.52 at 28.7°C, 0.51 at 29.7°C and 0.00 at 30.7°C. By the probit regression, the estimated critical temperature, the incubation temperature giving 50% males, was 29.4°C and the estimated critical duration, the incubation duration giving 50% males, was 54.7 days. At the fluctuating temperature, 27.7 (12h) and 30.7°C (12h), the sex ratio was 0.53. In the temperature shift experiment, the incubation temperature was 27.7°C for 19 days and then was shifted to 30.7°C. The obtained sex ratio,0.11, was close to the sex ratio expected at the mean temperature weighted by the developmental speed.