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

Characterizing how organisms respond to transient temperatures may further
our understanding of their susceptibility to climate change. Past studies
in the freshwater turtle, Trachemys scripta, have demonstrated that the
timing and duration of 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 snap exposure may affect gonadal development and
the production of males. We investigated how cold snap timing affects
gonadal gene expression in T. scripta embryos and how the duration of an
early cold snap influences resulting hatchling sex ratios. Results show
that responsiveness to cold changes rapidly across development, such that
genes that responded when exposure began on incubation day 14 responded
differently when exposure occurred just 4 or 8 days later. Sex ratio data
revealed that embryos experiencing an early cold snap also require a long
exposure (20 days) before most commit to testis development, suggesting
warm baseline temperatures may lower their sensitivity to later cold snap
exposures. These results highlight how individual responses to incubation
temperature can change rapidly across development in turtles and have
important effects on sex ratios.