Meeting Abstract
Birds begin embryonic life with an ectothermic phenotype and develop an endothermic phenotype after hatching. Precocial species, like the Pekin duck, make this transition rapidly upon hatching. Switching to endothermic phenotype requires high-functioning respiratory and cardiovascular systems to deliver sufficient oxygen from the environment and to the tissues. Here we measured tidal volume (VT), breathing frequency (ƒ), minute ventilation (VE), and whole-animal oxygen consumption (Vo2) during the developmental transition from externally pipped (EP) paranate to endothermic hatchling. We measured Vo2, VT, and ƒ as animals gradually cooled from 37.5C (EP) or 35C (hatchling) to 20C. An additional set of experiments examined hatchling responses to hypercapnia. Only hatchling Vo2 significantly increased in response to cooling. EP paranates had high ƒ that decreased with cooling, whereas hatchling ƒ was significantly lower and increased with cooling. Hatchling VT was significantly higher compared with that of EP paranates. During cooling, VT increased in both ages, but only at the coldest temperatures. Hatchling VE increased significantly during cooling, mainly due to increased ƒ, whereas EP paranate VE remained constant. In hatchlings, increasing CO2 to 4% resulted in ƒ, VT, and VE increasing significantly. We suggest that one potential constraint on an endothermic ventilatory response of EP paranates is the rigid eggshell, limiting air sac expansion during inhalation and constraining VT. Upon hatching, VT limitation is removed and the animal is able to increase VT, VE, Vo2 and exhibit an endothermic phenotype.
