Using naturalistic incubation temperatures to demonstrate how variation in the timing and continuity of heat wave exposure influences phenotype

Most organisms are exposed to bouts of warm temperatures during development, yet we know little about how variation in the timing and continuity of heat exposure influences biological processes. If heat waves increase in frequency and duration as predicted, it is necessary to understand how these bouts could affect thermally sensitive species, including reptiles with temperature-dependent sex determination (TSD). In a multi-year study using fluctuating temperatures, we exposed Trachemys scripta embryos to cooler, male-producing temperatures interspersed with warmer, female-producing temperatures (heat waves) that varied in either timing during development or continuity and then analyzed resulting sex ratios. We also quantified the expression of genes involved in testis differentiation (Dmrt1) and ovary differentiation (Cyp19A1) to determine how heat wave continuity affects the expression of genes involved in sexual differentiation. Heat waves applied during the middle of development pro...