The thermal performance curve for aerobic metabolism of a flying endotherm

Performance benefits of stable, warm muscles are believed to be important for the evolution of endothermy in mammals, birds, and flying insects. However, thermal performance curves have never been measured for a free-flying endotherm, as it is challenging to vary body temperatures of these animals, and maximal flight performance is difficult to elicit. We varied air temperatures and gas densities to manipulate thoracic temperatures of flying honey bees from 29-44°C, with low air densities used to increase flight metabolic rates to maximal values. Honey bees showed a clear thermal performance curve with an optimal temperature of 39°C. Maximal flight metabolic rates increased by ~2% per 1°C increase in thoracic temperature at suboptimal thoracic temperatures, but decreased ~5% per 1°C increase as the bees continued to heat up. This study provides the first quantification of the maximal metabolic performance benefit of thermoregulation in an endotherm. These data directly support aerobic capacity models for benefits of thermoregulation in honey bees, and suggest that improved aerobic capacity likely contributes to the multiple origins of endothermic heterothermy in bees and other insects.