Snapping turtles (Chelydra serpentina) demonstrate temperature-dependent sex determination (TSD): intermediate egg incubation temperatures (23-27 degreesC) produce males, while extreme temperatures produce females. Snapping turtles are also sexually dimorphic: adult males are typically larger than females. Previous researchers hypothesized that male-producing egg temperatures enhanced the growth rate of juvenile turtles, resulting in the adult dimorphism and potentially providing an adaptive benefit for TSD. In reptiles, the choice of ambient temperature can also influence growth. I measured the effect of egg incubation temperature on juvenile growth rate and water temperature choice of C. serpentina. Eggs were incubated in the laboratory at 21.5, 24.5, 27.5 or 30.5 degreesC to produce both sexes, all males, both sexes or all females, respectively. Egg temperature was linearly and negatively correlated with growth rate of both male and female juveniles. Thus, growth was enhanced, but not maximized, by male-producing egg temperatures. Egg temperature was also negatively correlated with juvenile temperature choice such that, on average, turtles from 21.5 degreesC eggs selected 28 degreesC water, while turtles from 30.5 degreesC eggs chose 24.5 degreesC water. Additionally, these temperature choices were highly repeatable, even following a 6 month hibernation period at 7 degreesC. Thus, while male egg temperatures do not directly maximize growth, multiple effects of embryonic temperature may combine to create long-lasting differences in the behavioral physiology of male and female C. serpentina. Such differences could be important to the ecology and evolution of TSD.
Identification of different critical embryonic periods to modify egg incubation temperature in mule ducks
