The sex of many reptile species is set by temperature. New research reported in the journal GENETICS identifies the first gene associated with temperature-dependent sex determination in any reptile. Variation at this gene in snapping turtles contributes to geographic differences in the way sex ratio is influenced by temperature. Understanding the genetics of sex determination could help predict how reptiles will evolve in response to climate change. In crocodiles, alligators, and certain lizard and turtle species, an embryo can become either a male or a female depending on the temperatures it experiences while in the egg. Rapid climate change may threaten the future of some of these species by skewing the sex ratio. For example, by some estimates temperature rises over the next century will cause painted turtles to produce only females. Such species may also evolve in response to climate change. Biologists are trying to understand how these animals will be affected by and adapt to rising global temperatures.

But little is known about how this temperature-dependent switch between ovaries and testes is regulated. To look for clues to the molecular mechanisms behind this process, study leader Turk Rhen (University of North Dakota) and his colleagues investigate how genes influence sex determination in common snapping turtles. The advantage of focusing on this rugged-looking North American native is that sex is determined in a brief five-day window during the 65-day egg incubation: the temperature-sensitive period. If the incubation temperature during the temperature-sensitive period is changed from a "male-producing temperature" (26.5°C or 79.7°F) to a "female-producing temperature" (31°C or 87.8°F), all the eggs will hatch into females.