Flexibility in body temperature rhythms of free-living natal mole-rats (Cryptomys hottentotus natalensis)

The subterranean niche is a specialised and particularly challenging environment to obtain direct physiological and behavioural measurements from free-living animals. Rhythmicity has been examined in many mole-rat species in the laboratory, but field reports are relatively scarce. We implanted Natal mole-rats with temperature loggers in summer and winter to record core body temperature (T_b), before releasing the animals again. Animals were recaptured after two months to recover the loggers. Natal mole-rats can maintain rhythmicity of their T_b in their natural habitat and display seasonal differences in their T_b rhythms. During winter mole-rats have unimodal T_b rhythms, whereas in summer many animals have bimodal T_b patterns, which may be related to temperatures in the foraging burrows close to the soil surface. Individuals from the same colonies frequently exhibited similar rhythms, especially in the larger colonies, which may indicate social entrainment of rhythms. Males and females differ in their seasonal variation of T_b, with males having more variation in winter, while the opposite was true for females. Entire colonies may undergo sporadic torpor bouts, presumably to conserve energy, but the trigger for these events is unknown. This is the first report of torpor occurring in an African mole-rat species. The ability to respond to environmental and social cues, while rhythms remain flexible, can provide an adaptive advantage to animals living in challenging and energetically demanding habitats.