The microclimate of the subterranean ecotope is rather stable. Particularly in the nest chamber, which in giant Zambian mole-
This constant temperature enables a lower basal rate of metabolism. In the thermally buffered environment of the underground “incubator,” it is possible to abandon complex and complicated morphological and physiological mechanisms of thermoregulation. Indeed, subterranean mammals tend to hypothermia (lowering the body temperature on average 89.6–96.8°F [32–36°C]). Body temperature is partly dependent upon the ambient temperature.
This relaxed thermoregulation (heterothermia) is most pronounced in the smallest (and the only hairless representative) among the subterranean mammals, the naked mole-
However, high humidity and relatively high temperatures, which can occur on sunny days in shallow foraging burrows, may result in thermoregulatory problems. In the absence of evaporative and convective cooling, overheating and thermal stress would seem to be inevitable, since burrowing is energetically demanding and most mammals can tolerate dry, warm climate better than humid, warm climate. Subterranean mammals living in warmer environments have high thermal conductance, which means that the animals may exchange heat (cool or warm themselves) relatively easily through direct physical contact between themselves and the soil.
As in poikilothermic reptiles, behavioral thermoregulation is of particular importance in heterothermic mammals. Thus, the animals can adapt timing and duration of their working activity to ambient temperatures in shallow burrows. Comparative and experimental physiological research of thermoregulation and energetics has a long tradition since McNab in 1966 first compared the metabolic rate of five subterranean rodent species and emphasized their shared adaptive convergence syndrome: low resting metabolic rate (involving also lower ventilation and heart rates than would be expected on the basis of body size), low body temperature, and high thermal conductance. Since then, additional physiological data have been obtained on diverse species of subterranean mammals supporting the earlier conclusions by McNab.