Confirmation of pleisiomorphic daily torpor in mammals: the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea)

Abstract

The characteristics of daily torpor were measured in the round-eared elephant shrew Macroscelides proboscideus (Macroscelidea) in response to ambient temperature and food deprivation. Elephant shrews are an ancient mammal order within a superordinal African clade including hyraxes, elephants, dugongs and the aardvark. M. proboscideus only employed torpor when deprived of food; torpor did not occur under an ad libitum diet at ambient temperatures of 10, 15 and 25 °C. Torpor bout duration ranged from <1 h to ca. 18 h. The times of entry into torpor were restricted to the scotophase, despite normothermic body temperature patterns indicating a rest phase coincident with the photophase. Full arousal was always achieved within the first 3 h of the photophase. When food deprived, the onset of the rest phase, and hence torpor, advanced with respect to the experimental photoperiod. The lowest torpor body temperature measured was 9.41 °C. Daily torpor in M. proboscideus confirms a pleisiomorphic origin of daily heterothermy. Torpor facilitates risk-averse foraging behaviour in these small omnivores by overcoming long-term energy shortfalls generated by the inherent variability of food availability in their semi-arid, El Niño-afflicted habitats.