HEAT WAVE TIMING, CONTINUITY, AND LENGTH AFFECT TEMPERATURE-DEPENDENT SEX DETERMINATION IN A FRESHWATER TURTLE

Publication Date

4-5-2019

Document Type

Poster

Degree Type

Graduate

Department

Biological Sciences

Mentor

Rachel Bowden

Mentor Department

Biological Sciences

Abstract

Climate change has the potential to threaten thermally sensitive species, such as reptiles with temperature-dependent sex determination (TSD), if heat waves increase in frequency and length as predicted. In species with TSD, temperature affects sex determination most acutely during the thermosensitive period (TSP), which falls in the middle third of development as defined by constant temperature studies. Presently, we know little about how the timing during development or continuity of heat waves affects sex determination. We hypothesized that exposure to daily fluctuations of 25±3°C (which produce all males) and heat waves of 29.5±3°C that varied in either timing during development or continuity would affect resulting sex ratios in Trachemys scripta. Exposure to a 15-day heat wave early or late in development did not significantly affect sex ratios (all male-biased), but heat waves occurring between days 24 and 45 resulted in an average sex ratio of 80% female. Further, the observed TSP was shorter than the TSP defined by constant temperature studies. Only the 12-day heat wave early in the TSP produced a female-biased sex ratio in the continuity study. Decreasing continuity resulted in male-biased sex ratios, resulting from continuity effects or lowered sensitivity later in the TSP. We also quantified Dmrt and aromatase expression following 6, 9, 12, and 16 days of heat wave exposure to determine how heat waves affect gene expression. Aromatase expression was significantly up-regulated after 12- and 16-day heat waves, while Dmrt1 expression did not significantly change over the course of the heat wave. These results clarify the timing and length of the TSP and provide information on the timing of up-regulation of aromatase expression under fluctuating conditions. Further, these data provide detailed insight into the physiological effects of climate change, in the form of heat waves, on species with TSD.

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