Control of breathing and respiratory gas exchange in ducks native to high altitude in the Andes

Abstract

We examined the control of breathing and respiratory gas exchange in six species of high-altitude ducks that independently colonized the high Andes. We compared ducks from high-altitude populations in Peru (Lake Titicaca at ∼3800 m above sea level; Chancay River at ∼3000-4100 m) to closely related populations or species from low altitude. Hypoxic ventilatory responses were measured shortly after capture at the native altitude. In general, ducks responded to acute hypoxia with robust increases in total ventilation and pulmonary O2 extraction. O2 consumption rates were maintained or increased slightly in acute hypoxia, despite ∼1-2°C reductions in body temperature in most species. Two high-altitude taxa – yellow-billed pintail and torrent duck – exhibited higher total ventilation than their low-altitude counterparts, and yellow-billed pintail exhibited greater increases in pulmonary O2 extraction in severe hypoxia. In contrast, three other high-altitude taxa – ruddy duck, cinnamon teal, speckled teal – had similar or slightly reduced total ventilation and pulmonary O2 extraction than low-altitude relatives. Arterial O2 saturation (SaO2) was elevated in yellow-billed pintails at moderate levels of hypoxia, but there were no differences in SaO2 in other high-altitude taxa compared to their close relatives. This finding suggests that improvements in SaO2 in hypoxia can require increases in both breathing and haemoglobin-O2 affinity, because yellow-billed pintail was the only high-altitude duck with concurrent increases in both traits compared to its low-altitude relative. Overall, our results suggest that distinct physiological strategies for coping with hypoxia can exist across different high-altitude lineages, even among those inhabiting very similar high-altitude habitats.