Climate Change and Temperature Dependant Sex Determination in Reptiles

Abstract. Despite increasing concern over the possible impact of global temperature change, there is little empirical
evidence of direct temperature effects on biotic interactions in natural systems. Clear aesment of the ecological and evolutionary impact of changing climatic temperature requires a natural system in which populations exhibit a direct unambiguous fitness response to thermal fction. I monitored nests of a population of palnted (Chrysemys pica) with
temperature-dependent sex determination to investigate the causal relationship between local climatic variation in temperature and offspring sex ratio. Consistent with theoretical predictions, annual offspring sex ratio was highly correlated with mean July air temperature, validating concerns about the effect of climate change on population demography. This correlation Implies that even modest increases in mean temperature (<2C) may drastically skew the sex ratio. Statistical evaluation of the variance in climate change indicates that an increase in mean temperature of 4 C would effectively eliminate production of male offspring. Quatitative genetic analyses and behavioral data suggest that populations with temperature-dependent sex determination may be unable to evolve rapidly enough to counteract the negative fitness consequences ofrapid global temperature change. Populations of species with temperature-dependent sex determination may serve as ideal indicators of the biological impact of global temperature change.