Hatching synchrony and survival in early life in the painted turtle, Chrysemys picta
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Synchrony in the timing of births is thought to have evolved as a general predator avoidance strategy. In turtles, synchronous hatching promotes synchronous emergence from the nest and may limit predation by swamping and confusing predators or simply dilute the per capita risk of predation. However, synchronization of hatching in natural nests is complicated by the occurrence of thermal gradients, which promote developmental asynchrony. In the first chapter of the thesis, I examined the potential for hatching synchrony in Chrysemys picta, a species in which the drive to hatch synchronously should be absent because neonates remain in the nest throughout the winter. I also assessed the mechanism by which synchrony occurs and explored potential trade-offs between synchronous hatching and performance. Although hatching synchrony did not occur, underdeveloped embryos attempted to catch-up to more advanced sibs via a mechanism consistent with shortening the incubation period. In addition, a trade-off between hatching synchronously and performance was evident. In the second chapter, I experimentally assessed the influence of accelerated hatching on hatching success, winter survival, and survival during terrestrial migration from the nest. I also examined the effects of incubation temperature on hatching success, and offspring sex and body size (carapace length and hatchling mass) on survival and migration time. Early-hatching individuals did not suffer fitness costs relative to their sibs at any stage considered in this study. Incubation treatment had a significant effect on migration time, but in the opposite direction that we predicted. Incubation temperature did not affect hatching success, and offspring sex did not affect survival when all treatment groups were considered. Incubation treatments significantly influenced offspring body size, which was negatively correlated with migration time, but had no effect on survival during terrestrial migration. Lack of a fitness cost associated with hatching synchrony is consistent with a single, predator avoidance origin for this trait and retention in C. picta via phylogenetic inertia.