Living at extremes: development at the edges of viable temperature under constant and fluctuating conditions.

In the painted turtle (Chrysemys picta) and the red-eared slider (Trachemys scripta), the temperature that eggs are exposed to during incubation influences many traits of the developing embryo. We tested the effect of fluctuating- versus constant-temperature incubation regimes at the high and low ends of the viable developmental temperature range to assess the effect of incubation environment on offspring development. Eggs were incubated in four treatments: 23 degrees C constant, 23 degrees +/- 3 degrees C, 31 degrees C constant, and 31 degrees +/- 3 degrees C. We assessed incubation duration, hatchling survival, growth, and immune function via a delayed-type hypersensitivity test. We predicted that fluctuations would accelerate developmental time at 23 degrees C and decelerate it at 31 degrees C and that these changes in incubation duration would influence offspring phenotype. We found that fluctuating incubation conditions affected developmental time at both temperatures and that survival, growth, and immune response were increased by temperature fluctuations. These results demonstrate that fluctuating temperatures have a differential impact on offspring phenotype when compared to constant temperatures, and they suggest that hatchling fitness is enhanced under conditions that more closely mimic natural incubation conditions.