Dissertation Research: The Evolutionary Significance of Environmental Sex Determination

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The proposed research is designed to identify factors that account for the adaptive significance of temperature-dependent sex determination (TSD) in reptiles and to assess the impact of environmental conditions on natural populations of reptiles with TSD. The influence of incubation temperature on growth and behavior of juveniles of two species of turtles (common snapping turtles, Chelydra serpentina and spiny softshell turtles, Trionyx spiniferus) will be examined. Correlation of one or both of these traits with incubation temperature and offspring sex would provide the first concrete evidence for the adaptive significance of TSD. The effects of current climatic temperatures on hatchling sex ratios of painted turtles (Chrysemys picta) also will be measured. This project will provide much-needed baseline information on how typical fluctuations in local summer temperatures influence the structure of natural populations with TSD. Additionally, to investigate implications of the predicted global warming on species with TSD, genetic variation, in response of sex ratios to incubation temperature will be examined. Without such genetic variation, species with TSD may be susceptible to extinction if local temperatures change sufficiently and rapidly to greatly skew the sex ratio. The synthesis of the results of these studies will elucidate the evolutionary significance of TSD.