SPENCER, R-J; JANZEN, F.J.; Iowa State University: Ecology and evolution of TSD in turtles: The value of long-term research and the effects of climate change.

Sex in many reptiles is determined permanently by environmental temperatures experienced during embryonic development. The unusual nature of this sex-determining system, with its potential to produce strongly-biased sex ratios, has generated considerable interest in its evolutionary origin and biological significance. Nonetheless, little is understood about the importance of many aspects of this temperature-dependent sex determination (TSD) that could lend insight into these fundamental questions. In particular, the impact of long-term climatic variation on crucial demographic parameters, namely offspring and population sex ratios, is unclear in reptiles with TSD. We have been studying a population of painted turtles on the Mississippi River for the last 16 years. Here we present data on clutch variation of sex ratios from individual female within years. We found that clutches are heavily biased towards one sex or the other in the first clutch of a season; however, second clutches predominantly consist of mixed sexes or are biased towards the other sex. An increasing production of males is not favored because ambient temperatures increase throughout the summer. We test several ecological, physiological and molecular theories to determine how convergence to mixed clutch sex ratios within years may evolve. We also present demographic models of how climate change may alter sex ratios and the potential effect on population parameters and dynamics.