Ventilation changes associated with hatching and maturation of an endothermic phenotype in the Pekin duck, Anas platyrhynchos domestica

Ventilation changes associated with hatching and maturation of au endothermic phenotype in the Pekin duck, Anas platyrhynchos domestica. Am J Physiol Regul Integr Comp Physiol 310: R766 R775, 2016. First published January 27, 2016; doi:10.1152/ajpregu.00274.2015. Precocial birds begin embryonic life with an ectothermic metabolic phenotype and rapidly develop an endothermic phenotype after hatching. Switching to a high-energy, endothermic phenotype requires high-functioning respiratory and cardiovascular systems to deliver sufficient environmental oxygen to the tissues. We measured tidal volume (V-T), breathing frequency (f), minute ventilation (Vu), and whole-animal oxygen consumption (V-o2,) in response to gradual cooling from 37.5 degrees C (externally pipped paranates, EP) or 35 degrees C (hatchlings) to 20 degrees C along with response to hypercapnia during developmental transition from an ectothermic, EP paranatc to endothermic hatchling. To examine potential eggshell constraints on EP ventilation, we repeated these experiments in artificially hatched early and late EP paranates. Hatchlings and artificially hatched late HP paranates were able to increase Vol significantly in response to cooling. EP paranates had high f that decreased with cooling, coupled with an unchanging low V-T and did not respond to hypercapnia. Hatchlings had significantly lower f and higher V-T and V-E that increased with cooling and hypercapnia. Its response to artificial hatching, all ventilation values quickly reached those of hatchlings and responded to hypercapnia. The timing of artificial hatching influenced the temperature response, with only artificially hatched late EP animals, exhibiting the hatchling ventilation response to cooling. We suggest one potential constraint on ventilatory responses of EP paranates is the rigid eggshell, limiting air sac expansion during inhalation and constraining V-T. Upon natural or artificial hatching, the V-T limitation is removed and the animal is able to increase V-T, V-E, and thus V-o2, and exhibit an endothermic phenotype.