Critical periods and pivotal temperatures for sexual differentiation in loggerhead sea turtles

Abstract

Eggs of loggerhead sea turtles, Caretta caretta, were incubated at constant temperatures ranging from 24 to 34 °C. At temperatures of 32 °C or above all embryos developed into females as judged by histology of the gonads. At 28 °C or below all developed into males. At 30 °C there were approximately equal numbers of both sexes; 30 °C therefore is the pivotal temperature for the thermal effects on sexual differentiation in this population of turtles. The direction of sexual differentiation is not determined by temperature throughout incubation but by the levels prevailing during a critical period. Experiments with temporary alterations of temperature, either upwards or downwards from the pivotal value, localized the critical period to somewhere between stages 12 and 22 of embryonic development. Definition of the critical period in sea turtles should prove useful both in further work on the theoretical aspects of the phenomenon and in conservation programmes for sea turtles.

Características da reprodução de tartarugas marinhas (Testudines, Cheloniidae) no litoral sul da Bahia, Brasil

“…Embora a duração média da incubação na área de estudo tenha sido inferior à duração pivotal, ela é maior do que a duração no litoral norte da Bahia. Uma vez que, quanto maior a temperatura e, portanto, menor a duração da incubação, maior a produção de fêmeas (Yntema & Mrosovsky 1982), os resultados ora apresentados sugerem que o litoral sul da Bahia gera mais machos em relação ao litoral norte deste estado. De fato já foi verificado que nas áreas de nidificação de C. caretta no litoral do Espírito Santo as durações médias da incubação são mais altas do que no litoral norte da Bahia, resultando em uma maior produção de filhotes machos (Baptistotte et al 1999).…”

Pivotal temperature and sexual dimorphism of Podocnemis expansa hatchlings (Testudines: Podocnemididae) from Bananal Island, Brazil

“…The remaining 89.2% may be attributed to variables such as multiple paternity, (VALENZUELA 2000), genetic influences (VALENZUELA 2001), as well as differing incubation temperatures (higher temperatures determine faster development;YNTEMA & MROSOVSKY 1982). Besides affecting gonadal differentiation, incubation temperatures may influence embryonary development which in turn reflects in the shape of the carapace (STANDING et al 1999).…”

Trace Metal and Organochlorine Pesticide Concentrations in Cold-Stunned Juvenile Kemp's Ridley Turtles (Lepidochelys kempii) from Cape Cod, Massachusetts

“…During each season, a subset of nests was sampled, including nests from each of the arribadas. Average nest temperatures during the middle third of the incubation period were used to predict sex ratios (Yntema and Mrosovsky 1982, Georges et al 1994, Hanson et al 1998) based on the pivotal temperature and transitional range of temperatures predicted for the Kemp's ridley (Aguilar 1987, Shaver et al 1988. The results are consistent with the sand temperature data and suggest that the hatcheries consistently produced overall female-biased sex ratios (Wibbels et al 2000a(Wibbels et al , 2000bGeis 2004;Wibbels 2007).…”