Latitudinal and Temperature-Dependent Variation in Embryonic Development Rate and Offspring Performance in a Freshwater Turtle.

The thermal environment of embryos differs significantly along a latitudinal cline, and the mechanism by which embryos respond to this geographic temperature variation has attracted increasing attention recently. Here, we carried out a common-garden experiment of egg incubation at two fluctuating temperature regimes to elucidate the latitudinal pattern and thermal dependence of the embryonic development rate and offspring performance in the Chinese soft-shelled turtle (Pelodiscus sinensis). Our results demonstrated significant temperature-by-population interactions on variations in the incubation period and hatchling righting response. The incubation period was shorter and the daily number of heart beats was higher in the medium- and high-latitude populations than in the low-latitude population at low incubation temperatures but not at high temperatures. Offspring from the medium- and high-latitude populations showed a faster righting response than those from the low-latitude population when incubated at low temperatures, whereas offspring from the high-latitude population showed a faster righting response than those from the medium-latitude population when incubated at high temperatures. This indicates that turtle embryos from different latitudinal locations may have evolved divergent thermal sensitivities of embryonic development in response to their respective nest environments.