Responsiveness to cold snaps by turtle embryos depends on exposure timing and duration

<p>Characterizing how organisms respond to transient temperatures may further our understanding of their susceptibility to climate change. In animals with temperature-dependent sex determination (TSD), unusual transient temperatures during incubation result in sex bias and may therefore impair population breeding capacity. Past studies in the red-eared slider turtle (<em>Trachemys scripta</em>) have demonstrated that the timing and duration of heat exposure ("heat waves") can have major implications for the response of genes involved in gonadal development and the production of female hatchlings. Yet, no study has considered how the response of these genes to transient cold exposure ("cold snaps") may affect gene expression and influence the resulting production of males.</p> <p>We investigated how cold snap timing and duration affect gonadal gene expression in <em>T. scripta</em> embryos. Additionally, we explored the effect of early cold snap exposure duration on resulting hatchling sex ratios. Results show that responsiveness to cool temperatures changes rapidly across development, such that genes that responded to cold snaps when exposure began on incubation day 14 responded differently when cold exposure occurred just 4 to 8 days later. The sex ratio experiment revealed that embryos experiencing an early cold snap also require a long exposure (&gt; 20 days) before most commit to testis development, further suggesting that early development under warm temperatures may lower their sensitivity to later cold snaps. These results highlight how individual responses to incubation temperature can change rapidly across development in turtles and have important effects on sex ratios. We discuss how variation in responsiveness to transient temperatures might help maintain mixed-sex ratios under variable thermal conditions in nature and may permit adaptive population responses to climate change.</p>