Does torpor of elephant shrews differ from that of other heterothermic mammals?

Abstract

Torpor bouts of elephant shrews are intermediate in duration to those of daily heterotherms and hibernating mammals, but their body temperatures (Tbs) and metabolic rates are very low and similar to those of hibernating mammals. We quantified the thermal physiology of the Cape rock elephant shrew ('Elephantulus edwardii'), a species endemic to high-altitude regions of South Africa, where winters are cold and wet, and tested whether it displays multiday torpor characteristic of hibernators at low ambient temperature (Ta). 'E. edwardii' regularly displayed torpor over a wide range of Tas. Occurrence of torpor and duration of torpor bouts increased with decreasing Ta. Whereas normothermic Tb was stable, Tb in torpid individuals fell with Ta. The mean Tb - Ta differential at the minimum Tb was 0.7°C, and the mean minimum Tb at Ta 8.9°C was 9.3°C. Duration of torpor bouts ranged from 6.5 to 44 h and was correlated negatively with Ta and Tb during torpor. Time required for the reduction of Tb to a Tb - Ta differential of <2.0°C was faster for >1-day torpor bouts than those lasting ≤1 day, suggesting that the duration of a bout might be determined at the beginning, not during, a bout. The nature of heterothermy in E. edwardii seems qualitatively similar to that of other elephant shrews, although torpor is somewhat deeper and longer in this species. Temporal patterns of torpor in E. edwardii differ from those of most cold-climate hibernators, likely for ecological rather than physiological reasons.