Body cooling and the diving capabilities of muskrats (Ondatra zibethicus): A test of the adaptive hypothermia hypothesis

摘要

We tested the hypothesis that immersion hypothermia enhances the diving capabilities of adult and juvenile muskrats by reducing rates of oxygen consumption (VO2). Declines in abdominal body temperature (T-b) comparable to those observed in nature (0.5-3.5 degrees C) were induced by pre-chilling animals in 6 degrees C water. Pre-chilling did not reduce diving VO2 of any animal tested in 10 degrees C or 30 degrees C water, irrespective of the nature of the dive. Most behavioural indices of dive performance, including average and cumulative dive times, were unaffected by Tb reduction in adults, but depressed in hypothermic juveniles (200-400g). 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 VO2 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. (c) 2006 Elsevier Inc. All rights reserved.