Oxygen transport during progressive hypoxia in high-altitude and sea-level waterfowl

Abstract

Under conditions of progressive hypoxia, oxygen transport was compared in bar-headed geese ( Anser indicus), a species which breeds on the Tibetan Plateau and migrates at altitudes up to 9200 m, and Pekin ducks ( Anas platyrhynchos, forma domestica), a similarly sized, sea-level waterfowl that does not fly. Pekin ducks showed no altitude-induced behavioral effects ( e.g., restlessness) up to 7620 m, while bar-headed geese tolerated 10,668 m with no observable changes. Ventilatory and cardiac responses to hypoxia as functions of Pa O 2 followed a typical hyperbolic contour, but the response began at almost 20 Torr lower in the bar-headed goose. Both ventilation and cardiac, output appeared to follow a common response curve for the two species, when the independent variable was expressed as arterial oxygen content. The goose had a high oxgen affinity hemoglobin, compared with the duck; the oxyhemoglobin dissociation curves of both shifted slightly to the right as a result of acclimation to 5640 m; but only the duck developed erythrocytosis as a consequence of acclimation. User sea level conditions the duck maintained a higher venous P O 2 , but with acute hypoxic exposure P v O 2 was higher in the goose. Following acclimation, cardiac output in the duck was lower than in the pre-acclimatized state, but in the goose it was higher up to the altitude at which it migrates. The selective pressures leading to the evolution of favorable oxygen transport in the bar-headed goose are discussed.