SPENCER, R-J; Iowa State University: Adaptive significance of TSD in turtles: Sex specific fitness advantages of overwintering in painted turtles.

Temperature dependent sex determination (TSD) has evolved independently in many taxa. Underlying the theory of an adaptive significance of TSD is that there are sex specific fitness advantages of particular incubation temperatures. These advantages have primarily focused on immediate (egg survival) or long (growth and maturity) term effects of incubation temperature. However, Chrysemys picta hatchlings overwinter in the nest and each nest potentially experiences different temperature regimes for upwards of a year. Hatchlings must rely on initial yolk reserves during this period and ground temperatures can fluctuate between -10�C and 35�C. I determined whether sex specific differences in survival and performance of C. picta existed at different overwintering temperature regimes. Clutch mates were separated into either a �hot� or �cold overwintering temperature regimes and I determined individual survival, metabolic rates and the amount of yolk reserves used from fall-spring. I found that males had lower metabolic rates than females in the cooler fall and spring simulated nest temperatures. Similarly, females in the warmer fall and spring simulated nest temperatures had lower metabolic rates than males. Metabolic rates in the winter simulated nest temperatures were extremely low and not significantly different between treatments. Survival rates and yolk reserve utilization was also different between treatments. My results suggests that the maintenance of TSD may be adaptive for overwintering in C. picta because metabolic rates, energy use and survival were sex specific to particular temperature regimes. Consequently, the best adapted sex is produced irrespective of nest site selection.