COLBERT, P; SPENCER, R-J; JANZEN, F.J.; Iowa State University: Hatch or Wait II: Synchronous hatching is not a predator-avoidance strategy in turtles.

Synchrony in the timing of births may have evolved as a predator-avoidance strategy as it dilutes the risk of predation upon vulnerable newborn and naive young. Synchronous hatching of sibs within a nest occurs in birds and turtles. However, the costs of synchronous hatching to some individuals include reduced development. Some species of turtle remain in the nest for upwards of a year after hatching (overwintering) and selection for synchronous hatching to facilitate group emergence would not be strong. We induced developmental asynchrony within clutches of the painted turtle, Chrysemys picta, which overwinters within the nest and emerges the following spring. Asynchrony was established by dividing clutches and incubating them at either 26C or 30C. Eggs were then reunited with their clutch-mates and hatching occurred synchronously in some of these groups. Synchrony occurred because less advanced eggs hatched earlier than the control embryos. We also tested whether turtles that hatched earlier were developmentally less advanced than their sibs by conducting correction trials. Recently hatched turtles were placed on their carapace and the time spent correcting their position was measured. We found that, despite clutch effects, turtles that emerged earlier than their sibs were less coordinated and spent longer time correcting themselves. Thus, less advanced embryos within a clutch hatch prematurely to ensure synchrony of hatching. Synchronous hatching in C. picta contradicts the theory that synchronous hatching aids quick emergence and group formation. We predict that synchronous hatching may be a primitive trait that is widespread among turtles.