48.1 Thursday, Jan. 5 Are intraspecific correlations between minimum and maximum metabolic output in birds consistent with the aerobic capacity model for the evolution of endothermy? SWANSON, David L*; THOMAS, Nathan E.; Univ. of South Dakota, Vermillion; Shippensburg Univ., Shippensburg, PA email@example.com
The underlying assumption of the aerobic capacity model for the evolution of endothermy is that basal (BMR) and maximal aerobic metabolic rates are phenotypically correlated. However, because BMR is largely a function of central organs whereas maximal metabolic output is largely a function of skeletal muscles, the mechanistic underpinnings for their correlation is not obvious. Interspecific studies in birds generally support a phenotypic correlation between BMR and maximal metabolic output. If the aerobic capacity model is valid, these phenotypic correlations should also extend to intraspecific comparisons. We measured BMR, Msum (maximum thermoregulatory metabolic rate) and MMR (maximum exercise metabolic rate in a hop-flutter chamber) in winter for dark-eyed juncos (Junco hyemalis) and American goldfinches (Carduelis tristis; Msum and MMR only) and examined correlations among these variables. For both raw metabolic rates and residuals from allometric regressions, BMR was not significantly correlated with either Msum or MMR in juncos. Moreover, no significant correlation between Msum and MMR or their allometric residuals occurred for either species. These data suggest that central organ and exercise organ metabolic levels are not inextricably linked and that muscular capacities for exercise and shivering do not necessarily vary in tandem in individual birds. Why intraspecific and interspecific avian studies show differing results and the significance of these differences to the aerobic capacity model are unknown, and resolution of these questions will require additional studies of potential mechanistic links between minimal and maximal metabolic output.