HUDDLING BEHAVIOR FACILITATES HOMEOTHERMY IN THE NAKED MOLE RAT HETEROCEPHALUS-GLABER

Heterocephalus glaber (the naked mole rat) is a highly social mammal, living in large underground colonies in equatorial Africa. Isolated naked mole rats exhibit unusual thermoregulation and cannot regulate body temperature (T(b)). Thermoregulatory parameters, namely VO2, evaporative water loss (EWL), and T(b), were therefore examined when these animals were housed in groups ranging from two to eight animals. Oxygen consumption at low ambient temperatures (T(a)'s), irrespective of the experimental group size, increased with increasing T(a) in a poikilothermic manner. Changes in VO2 with increasing T(a) switched to an endothermic pattern at T(a)'s ranging from 25-degrees-C (for groups of eight) to 27-degrees-C (for pairs). Huddling behavior confers savings in both energy expenditure and evaporative water loss. These are most pronounced at high T(a)'s. For instance, at T(a) = 32-degrees-C (within the "thermoneutral zone"), groups of eight animals use 78% of the Vo2 and 69% of EWL used by pairs. Body temperature of animals housed in pairs is directly proportional to T(a) over the entire experimental T(a) range (14-degrees-37-degrees-C). Over the T(a) range normally encountered in their warm equatorial burrows (29-degrees-32-degrees-C), animals that were housed in groups of four or more tightly controlled T(b) (within 1-degrees-C). Data presented here suggest that huddling behavior not only saves energy and water, so essential in an arid environment where food is sparsely distributed, but huddling also plays a very important thermoregulatory role in these otherwise nonendothermic mammals. Huddling ensures that, in their natural habitat, naked mole rats are able to control T(b) and are indeed homeotherms.