Development of Endothermy: Getting to the Heart of the Problem
Precocial birds develop from ectothermy to endothermy during the final days of incubation and the first 24 hours after hatching. Onset of endothermy and ability to thermoregulate are coupled with ductus arteriosus closure and an upregulation of metabolic activity. The present study examined changes in whole animal oxygen consumption as an indicator of endothermic capacity in precocial Pekin ducklings (Anas pekin). Parameters of heart mass, hemoglobin, and hematocrit were measured to elucidate changes in blood oxygen carrying capacity. Mitochondrial respiration in permeabilized cardiac fibers from left and right ventricles was measured to examine cellular level metabolic capacity. Measurements were made on day 24 of incubation, at internal and external pipping stages, and at 12 to 24 hours after hatching. When exposed to cold temperature, ducklings maintained an elevated body temperature and metabolic rate only after hatching. As ducks aged, there was significant increase in body mass, coupled with a decrease in yolk sac mass. No significant differences were documented in hemoglobin or hematocrit between age groups. At the onset of endothermy, hatchling relative ventricle size was significantly larger than earlier stages of development. Increased heart mass was associated with increased cardiac oxidative phosphorylation (OXPHOS) through Complex I in the left, but not right ventricle. In hatchlingsn OXPHOS through Complex I + II within the left ventricle increased significantly compared with the right. These results suggest increased ventricle size and mitochondrial respiration within the left ventricle of hatchlings occurs in response to increased energy demand brought about by acquisition of endothermy and the closing of the ductus arteriosus. This project is funded by NSF OS 1146758 (EMD).