Journal
JOURNAL OF EXPERIMENTAL BIOLOGY
Volume 211, Issue 8, Pages 1326-1335Publisher
COMPANY OF BIOLOGISTS LTD
DOI: 10.1242/jeb.015958
Keywords
thermoregulation; thermal windows; respiration; breathing pattern
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The objectives of this study were to compare the thermoregulatory, metabolic and ventilatory responses to hypoxia of the high altitude bar-headed goose with low altitude waterfowl. All birds were found to reduce body temperature (T-b) during hypoxia, by up to 1 - 1.5 degrees C in severe hypoxia. During prolonged hypoxia, T-b stabilized at a new lower temperature. A regulated increase in heat loss contributed to Tb depression as reflected by increases in bill surface temperatures (up to 5 degrees C) during hypoxia. Bill warming required peripheral chemoreceptor inputs, since vagotomy abolished this response to hypoxia. T-b depression could still occur without bill warming, however, because vagotomized birds reduced T-b as much as intact birds. Compared to both greylag geese and pekin ducks, bar-headed geese required more severe hypoxia to initiate T-b depression and heat loss from the bill. However, when T-b depression or bill warming were expressed relative to arterial O-2 concentration ( rather than inspired O-2) all species were similar; this suggests that enhanced O-2 loading, rather than differences in thermoregulatory control centres, reduces T-b depression during hypoxia in bar-headed geese. Correspondingly, bar-headed geese maintained higher rates of metabolism during severe hypoxia ( 7% inspired O-2), but this was only partly due to differences in T-b. Time domains of the hypoxic ventilatory response also appeared to differ between bar-headed geese and low altitude species. Overall, our results suggest that birds can adjust peripheral heat dissipation to facilitate T-b depression during hypoxia, and that bar-headed geese minimize T-b and metabolic depression as a result of evolutionary adaptations that enhance O-2 transport.
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