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Cardiorespiratory responses to hypoxia in high- and low-altitude geese and ducks

University of British Columbia

High-altitude (HA) life is challenging due to the reduced partial pressure of oxygen (hypoxia). Hence, HA vertebrates have evolved increased capacities in their oxygen transport cascade enhancing oxygen transfer. The extent of interspecies variation in these responses within waterfowl, a taxon prolific at HA, remains largely unknown. This thesis investigated 17 waterfowl groups at different altitudes to address the overarching hypotheses that waterfowl use multiple cardiorespiratory strategies to maintain oxygen supply during hypoxia, and that HA exposure alters the waterfowl hypoxic ventilatory and cardiovascular responses. A comprehensive analysis of metabolic, cardiovascular, and ventilatory responses to progressive decreases in equivalent fractional composition of inspired oxygen was made on resting low-altitude (LA) barnacle geese, LA bar-headed geese, HA bar-headed geese, Andean geese, and crested ducks. Andean geese and crested ducks, lifelong HA residents, exhibited fundamentally different mechanisms for maintaining oxygen supply during hypoxia than bar-headed geese, transient HA migrators. Bar-headed geese robustly increased ventilation and heart rate, whereas Andean species increased lung oxygen extraction and stroke volume. Also, HA-reared bar-headed geese exhibited reduced oxygen consumption during hypoxia compared to LA-reared bar-headed geese. Similar cardiovascular studies were performed on five HA duck species (yellow-billed pintail, cinnamon teal, ruddy duck, speckled teal, and Puna teal) in Peru and six related LA duck species (northern pintail, cinnamon teal, ruddy duck, green-winged teal, gadwall, and mallard duck) in the USA. Heart rate and oxygen pulse remained generally unchanged. Instead, most HA ducks exhibited higher blood-oxygen carrying capacity and lower heart rate variability than LA ducks. While heart rate, stroke volume, oxygen pulse, and blood-oxygen carrying capacity contributed to all 17 groups’ hypoxic cardiovascular responses, the predominant responses were increased stroke volume and, in HA taxa, blood-oxygen carrying capacity. Only bar-headed geese increased heart rate appreciably. This thesis identifies multiple cardiovascular and respiratory strategies by which waterfowl maintain oxygen supply during hypoxia, and provides insight into how HA rearing impacts these responses. This thesis also suggests that short-term HA performance utilizes primarily functional enhancements (e.g. rapid heart rate and ventilation increases), whereas lifelong HA residency is supported predominantly by structural changes (e.g. lung and cardiac morphology enhancements).

Text

2016-07-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/58484

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/