We measured temperature-induced differences in metabolic rates and growth by embryos of three turtle species, Macrochelys temminckii, Trachemys scripta, and Apalone spinifera, at different, constant, temperatures. Oxygen consumption rate (VO2) was measured during development and used to characterize changes in metabolism and calculate total O2 consumption. Results from eggs incubated at different temperatures were used to calculate Q10s at different stages of development and to look for evidence of metabolic compensation. Total O2 consumption over the course of incubation was lowest at high incubation temperatures, and late-term metabolic rate Q10s were <2 in all three species. Both results were consistent with positive metabolic compensation. However, incubation temperature effects on egg mass-corrected hatchling size varied among species. Apalone spinifera hatchling mass was unaffected by temperature, whereas T. scripta mass was greatest at high temperatures and M. temminckii mass was lowest at high temperatures. Hatchling mass？:？length relationships tended to correlate negatively with temperature in all three species. Although we cannot reject positive metabolic compensation as a contributor to the observed VO2 patterns, there is precedence for drawing the more parsimonious conclusion that differences in yolk-free size alone produced the observed incubation temperature differences without energetic canalization by temperature acclimation during incubation. 1. Introduction Although the suite of biochemical activities that contributes to an organism’s metabolism is complex and therefore challenging to model [1], strong relationships exist between body temperature and whole-organism metabolic rate [2]. Various thermoregulatory mechanisms are employed by animals to dissociate body temperature from ambient temperature. Endothermy has evolved repeatedly as a physiological means of surviving suboptimal thermal conditions, but ectothermic species often rely primarily on behavioral strategies to regulate body temperature. In addition to behavior, however, ectotherms may exhibit physiological mechanisms to address thermal constraints of their environment. Solutions for surviving inhospitable temperatures may include manipulating biochemical reaction rates by varying enzyme concentrations or receptor densities, production of chaperone proteins to increase the range of temperatures over which target enzymes remain functional [3], changing the composition of cell membranes to affect permeability and (rarely) producing temperature-specific isozymes [4–6]. In
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