Meeting Abstract
Species that occur across broad geographic ranges often experience substantial variation in ambient temperature. Because temperature is critical to many biological functions, how different populations have adapted to local thermal environments has been an important question in evolutionary biology. This is particularly important in species with temperature-dependent sex determination (TSD), whereby developmental temperature has a direct impact on the primary sex ratio, and hence population demographics. We used the painted turtle (Chrysemys picta) to assess how TSD is adjusted across widespread populations that experience different climates. Specifically, we test hypotheses derived from a long-standing theoretical framework that primary sex ratios under TSD are adjusted through changes in the sex determining response of embryos to incubation temperature and/or maternal nesting behavior. Lab experiments aimed at quantifying sex-determining reaction norms across seven populations (Illinois, Minnesota, Kansas, Nebraska, New Mexico, Idaho, Oregon) provide little evidence that populations differ in how developmental temperature affects offspring sex ratio; pivotal temperatures were approximately 28 C across all populations. Thus, TSD may be adjusted across populations via maternal nesting behavior. To address this, we have collected field data on nest microhabitat (e.g., nest temperature, overstory cover, depth) and the timing of nesting at six of our study sites. These data will provide a comprehensive understanding of how long-lived taxa with TSD accommodate geographic variation in temperature, and how they may adjust to predicted climate change scenarios in the future.
