Development of endothermy and concomitant increases in cardiac and skeletal muscle mitochondrial respiration in the precocial Pekin duck (Anas platyrhynchos domestica)

Abstract

Attaining endothermic homeothermy occurs at different times post-hatching in birds and is associated with maturation of metabolic and aerobic capacity. Simultaneous measurements at the organism, organ, and cellular levels during the transition to endothermy reveal means by which this change in phenotype occurs. We examined development of endothermy in precocial Pekin ducks (Anas platyrhynchos domestica) by measuring whole animal O2 consumption (V̇o2) as animals cooled from 35 to 15°C. We measured heart ventricle mass, an indicator of O2 delivery capacity, and mitochondrial respiration in permeabilized skeletal and cardiac muscle to elucidate associated changes in mitochondrial capacities at the cellular level. We examined animals on day 24 of incubation through 7 days post hatching (dph). V̇o2 of embryos decreased when cooling from 35 to 15°C; V̇o2 of hatchlings, beginning on day 0 dph increased during cooling with a lower critical temperature of 32°C. Yolk-free body mass did not change between internal pipping and hatching but, the heart and thigh skeletal muscle grew at faster rates than the rest of the body as the animals transitioned from an externally pipped paranate to a hatchling. Large changes in OXPHOS capacity occurred during ontogeny in both thigh muscles, the primary site of shivering, and cardiac ventricles. Thus, increased metabolic capacity necessary to attain endothermy was associated with augmented metabolic capacity of the tissue and augmented increasing O2 delivery capacity, both of which were attained rapidly at hatching.