Temporal Effects of Heat Waves on Sex Ratios and Gene Expression in a Freshwater Turtle
As climate change progresses, average global temperatures are predicted to continue to increase as a result of longer, more frequent heat waves. This thermal variability arising from climate change has the potential to threaten thermally sensitive ectotherms, such as reptiles with temperature-dependent sex determination (TSD). In many turtle species with TSD, cooler temperatures produce males and warmer temperatures produce females by inducing the expression of testis and ovary associated genes, respectively. Dmrt1 is one such gene associated with testis development while aromatase is associated with ovary development. I hypothesized that the timing of when embryos experience a heat wave during development will affect their propensity to develop as males or females by affecting the expression of Dmrt1 and aromatase. Using ecologically relevant fluctuating temperature treatments, I varied the timing to which red-eared slider (Trachemys scripta) embryos were exposed to 15-day heat waves during incubation and analyzed resulting sex ratios. I also collected embryonic tissues during heat waves of 15 and 20 days to analyze Dmrt1 and aromatase expression. I found that heat waves that at least partially occurred during days 20-40 of development produced mostly females, with a heat wave applied during days 24-38 resulting in 89% females. A heat wave applied during days 38-52 of development only produced 6% females, despite it occurring during the predicted window over which sex determination should still be sensitive to temperature. I also found that aromatase was up-regulated in response to a heat wave of 20 days while Dmrt1 was up-regulated in the absence of a simulated heat wave. Overall, these results provide insights on the timing and length of the period over which sex determination is sensitive to temperature, and suggest that the window of sensitivity is likely to vary depending upon the thermal conditions experienced during development. These results also clarify the timing of up-regulation of certain sex determining genes and further our understanding of how sex ratios in species with TSD might respond to climate change.
Breitenbach, Anthony, "Temporal Effects of Heat Waves on Sex Ratios and Gene Expression in a Freshwater Turtle" (2018). University Research Symposium. 19.