Interspecific comparisons of physiological parameters such as metabolic rates and temperature regulation, with ecological parameters such as activity patterns and thermoregulatory behavior, often demonstrate that physiology and behavior co-evolve to meet ecological challenges. Hatchling turtles are vulnerable to abiotic hazards such as temperature extremes and desiccation, as they have high surface area-volume ratios, poor locomotor abilities, and cannot easily dig deeply into the substrate. Measuring metabolic rates (SMR), Q10 coefficients, and reaction norm patterns among hatchlings of eleven species allowed us to test for a correlation with post-hatching activity associated with overwintering patterns, between turtles that dramatically differ ecologically. Turtle eggs were either collected locally, incubated and hatched, or hatchlings were bought from breeders. The metabolic rates of hatchlings, approximately 1 month old, were measured as the rate of oxygen consumption (VO2) at 20, 22, 24, 26, 28, and 30oC, using closed–flow respirometry. We performed Kendall’s Coefficient of Rank Correlation tests to compare 24oC, 26oC and 28oC SMR rankings to our predicted SMR rankings, based on overwintering strategy. We calculated Q10s for each species using SMR values at 20oC and 30oC and visually inspected reaction norms.
Results/Conclusions
We attempted to extend previously successful work showing that patterns of cold tolerance, desiccation tolerance, and rehydration ability generally match the overwintering microhabitat of hatchlings of multiple species of turtles, by exploring the physiology of turtle hatchlings soon after hatching and before overwintering. However, we found little agreement between the SMR, Q10 coefficient, or reaction norm patterns we predicted and those we observed in laboratory experiments. There were no significant relationships between our predicted SMR species rankings and actual SMR rankings at 24oC (Τ = 0.10, P = 0.75), 26oC (Τ = 0.38, P = 0.12) or 28oC (Τ = 0.38, P = 0.12). As predicted, the highest Q10s were among species that are active throughout the winter, except one species, that is active in water throughout the winter and had a relatively low Q10 (Emydura subglobosa). Hatchlings that remain active in winter, Apalone ferox and Testudo marginata, also had had steep reaction norms as predicted, and the species that become inactive while overwintering terrestrially, either in the nest or by digging their own refugia, had relatively flat reaction norms. Unexpectedly, one species (Emydura subglobosa) which remains active in water also had relatively flat reaction norms.