Heterothermy in elephant shrews, Elephantulus spp. (Macroscelidea): Daily torpor or hibernation?

The physiological parameters of heterothermy (e.g. minimum body temperature and oxygen consumption, percentage metabolic reduction, and bout length) were measured in two species of Elephantulus elephant shrews (Elephantulus myurus and Elephantulus rozeti; Macroscelidea) as a function of ambient temperature. Both species displayed deep torpor whereby the body temperatures of ca. 5 °C and oxygen consumption as low as 2% of basal metabolic rate were attained. Torpor bout length (n = 57 bouts) never exceeded 24 h. These data are characteristic of both hibernation (minimum body temperature and metabolism) and daily torpor (bout length), and argue that these two physiological responses may not necessarily have separate evolutionary origins.