DODD, K. L.*; MURDOCK, C.; WIBBELS, T.; Univ. of Alabama, Birmingham; Univ. of Alabama, Birmingham; Univ. of Alabama, Birmingham: Clutch-specific Variation of Sex Ratios in a Reptile with Temperature-dependent Sex Determination

Many reptiles exhibit temperature-dependent sex determination (TSD) in which the incubation temperature of the egg determines the sex of the embryo. The physiology of TSD is not well understood. However, estrogen has been hypothesized to play a key role. It has been suggested that estrogen in the yolk can affect the sex ratios by altering the pivotal temperature (i.e., the temperature producing a 1:1 sex ratio) and by causing increases in the numbers of females toward the end of the nesting season. This study analyzed sex ratios of Trachemys scripta, a turtle with TSD, by incubating eggs at the pivotal temperature. For each of three nesting seasons (2000, 2001, 2003), sex ratios were examined in forty to fifty-five clutches throughout the nesting season. The results indicate that the pivotal temperature in T. scripta varies between clutches. Data from the 2003 season supported the hypothesis that the pivotal temperature may vary toward the end of the season, resulting in the production of more females. However, data from the 2000 and 2001 season did not support this hypothesis.