FAQ : Detailed View! Is there a SPECIFIC temperature to determine whether the egg of a sea turtle is female? For all sea turtles, the direction of sexual differentiation is dependent on sand temperatures during the middle third of incubation. Warmer sand temperatures produce more or all female hatchlings, and cooler sand temperatures produce more or all males. The pivotal temperature is the constant incubation temperature that produces equal numbers of male and female hatchling sea turtles. The transitional range of temperatures (TRT) is the range of temperatures that produces both sexes (for more details on these standardized definitions, see Mrosovsky and Pieau 1991). Only a handful of studies have determined the pivotal temperature and TRT for certain sea turtle populations. So far, the pivotal temperature seems to be nearly always close to 29 °C or 82 °F (see Mrosovsky 1994 for more details). On the other hand, the TRT seems to vary quite a bit more. For example, leatherback sea turtles from French Guiana in South America have a transitional range of temperatures that span <0.75 °C or <1 °F, whereas green sea turtles from Suriname have a transitional range of temperature >3 °C or >6 °F (Mrosovsky et al. 1984; Chevalier et al. 1999). Because of the variability of the TRT in different sea turtle species and populations, and because we have studied incubation temperatures and sex ratio in only a few different populations, it is impossible to say what egg incubation temperature will absolutely produce a female sea turtle hatchling. Probably, incubation temperatures greater than 33 °C or 91.4 °F are likely to produce only females, but it is not known for sure. There is an alternative, sure-fire way to produce female sea turtle hatchlings from developing eggs: simply place a drop of estrogen on the egg during the first half of incubation (Crews et al. 1994). Chevalier, J., M. H. Godfrey, and M. Girondot. 1999. Significant difference of temperature-dependent sex determination between French Guiana (Atlantic) and Playa Grande (Costa-Rica, Pacific) leatherbacks (Dermochelys coriacea). Annales des Sciences Naturelles 20:147-152. Crews, D., J. M. Bergeron, J. J. Bull, D. Flores, A. Tousignant, J. K. Skipper, and T. Wibbels. 1994. Temperature-dependent sex determination in reptiles: proximate mechanisms, ultimate outcomes, and practical applications. Developmental Genetics 15:297-312. Mrosovsky, N. 1994. Sex ratios of sea turtles. Journal of Experimental Zoology 270:16-27. Mrosovsky, N., P. H. Dutton, and C. P. Whitmore. 1984. Sex ratios of two species of sea turtle nesting in Suriname. Canadian Journal of Zoology 62:2227-2239. Mrosovsky, N., and C. Pieau. 1991. Transitional range of temperature, pivotal temperatures and thermosensitive stages for sex determination in reptiles. Amphibia-Reptilia 12:169-179. Answer by Matthew Godfrey (North Carolina Wildlife Resources Commission) Submitted by: abe woo -- abe_woo@hotmail.com Search Looking for something in particular? More search options