Abstract
We tested the hypothesis that immersion hypothermia enhances the diving capabilities of adult and juvenile muskrats by reducing rates of oxygen consumption (V˙O 2). Declines in abdominal body temperature ( T b) comparable to those observed in nature (0.5–3.5 °C) were induced by pre-chilling animals in 6 °C water. Pre-chilling did not reduce diving V˙O 2 of any animal tested in 10 °C or 30 °C water, irrespective of the nature of the dive. Most behavioural indices of dive performance, including average and cumulative dive times, were unaffected by T b reduction in adults, but depressed in hypothermic juveniles (200–400 g). Hypothermia reduced diving heart rate only on short (< 25 s) dives (16% reduction, P = 0.01), but did not affect the temporal onset of diving bradycardia. Post-immersion V˙O 2 was higher for pre-chilled than for normothermic muskrats, but the difference became insignificant on longer (> 90 s) dives. Our findings suggest that the mild hypothermia experienced by muskrats in nature has minimal effect on diving and post-immersion metabolic costs, and thus has little impact on the dive performance of this northern semi-aquatic mammal.
Published Version
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