NSF Award
2114111
Most organisms respond to environmental temperatures, and these responses are typically studied by comparing individuals held at one temperature to individuals held at a different temperature. This approach misses two important points: 1) temperatures in nature are often variable and exposure to a given temperature can be transient, and 2) it does a poor job quantifying variation in how long it takes individuals to respond to temperature. This project focuses on understanding why some individuals respond to a short exposure to a given temperature, while others do not. Studies will be conducted using the red-eared slider turtle (Trachemys scripta), where incubation temperatures affect sex determination, which provides a clear signal (i.e., formation of a testis or ovary) of how individuals responded to temperature. Specifically, cool incubation temperatures induce testis development and warm incubation temperatures induce ovary development. It is also established that higher levels of estrogens in the egg increase the likelihood that the embryos will develop ovaries. Under natural conditions, embryos routinely experience both testis and ovary inducing temperatures, so studies are aimed at deciphering how long of an exposure to warmer temperatures is necessary to induce ovary development and whether elevated estrogen levels reduce the exposure requirement. Advancing our understanding of how temperature affects sex determination will assist efforts to mitigate the effect of climate change on thermally sensitive species. The project will train a postdoctoral researcher, graduate and undergraduate students, and will engage pre-college students in STEM-related activities. <br/><br/>Recent studies have demonstrated that temperature-dependent sex determination involves epigenetic regulation of critical transcription factors that determine sex. In the red-eared slider turtle (Trachemys scripta), the histone demethylase Kdm6b removes repressive histones marks from the promoter of Dmrt1, which is a conserved regulator of testis development. For this species, testis development is induced at cool incubation temperatures (below 29˚C). This proposal examines how sex determination occurs under ecologically relevant conditions where incubation temperatures fluctuate between those that induce either testis production or ovary production. Projects will focus on the temporal aspect of the response to temperatures since it is established that exposure to specific incubation temperatures is transient in nature and individual embryos vary in whether their gonadal fate is influenced by brief exposures (e.g., heatwaves). Additionally, projects will investigate whether maternal estrogens affect the duration of exposure necessary to induce ovarian development. By characterizing how the expression of genes involved in gonadal differentiation respond to transient exposure to incubation temperature and how estrogens my influence that response, studies will begin to disentangle how molecular responses to warm and cool temperature may vary independently. Understanding how an organism responds to thermal variation will strengthen our understanding of how environmental temperatures regulate biological processes such as sex determination.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
