LTREB: Long-term Research on Environmental Gender Determination in a Model System (Chrysemys)

Iowa State University, Ames IA

Investigators

Abstract

0089680 Janzen In contrast to the sex-determining mechanisms of most vertebrates, sex in many reptiles is determined by environmental temperatures determined during embryonic development. The unusual nature of this sex-determination system, with its potential to produce strongly-biased sex rations, 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 demograpic parameters, namely offspring and population sex ratios, is unclear in reptiles with TSD. Furthermore, the role of nest-site choice in this system is virtually unexplored, especially across the long reproductive lifespans that characterize these taxa, despite its significance in most theoretical models of sex-ratio evolution. Predation, biased or otherwise, also occupies a significant role in theoretical models of population dynamics but its impact on offspring sex ratio is unknown. Organisms with TSD are ideal model systems with which to explore the impact of these major factors on population dynamics and sex-ratio evolution in nature. The proposed LTREB research will investigate several significant aspects of the evolutionary ecology of TSD in a natural population of long-lived painted turtles, which has been studied in detail since 1988. First, how does long-term climatic variation covary with annual cohort sex ratio and thus influence population demography and the evolution of TSD? Second, do females with TSD exhibit long-term ontogenetic repeatability of nst-site choice with respect to available thermal environments and thereby provide a target for evolutionary response to sex-ratio selection imposed by rapid climate change and human habitat modification? Third, what are the long-term spatio-temporal dynamics of nest predation and offspring sex ratio in a natural population with TSD and thus their impacts on population demography and sex-ratio evolution? Obtaining answers to such questions assumes greater urgency given rapid climate change and human habitat modification.