Comparative aspects of the metabolism and thermal biology of elephant‐shrews (Macroscelidea)

Abstract

ABSTRACTThe metabolic rates of elephant‐shrews are typical of eutherian mammals and follow allometric relationships. They do not exhibit ‘primitive’ characteristics in relation to thermal biology as shown by other insectivores, and their reduced metabolic rates are interpreted as adaptive responses to habitat variables. Stable body temperatures are maintained over a wide range of environmental extremes. Hyperthermia is prevented by evaporative water loss and peripheral vasodilation, whereas hypothermia is probably more widespread than current data suggest. Elephantulus rozeti from the Atlas Mountains of North Africa has been shown to exhibit spontaneous daily torpor. Although the metabolic rates of macroscelids approximate those of tupaiids, they differ in maintaining a high stable body temperature below the thermoneutral zone.The ecophysiology of the species comprising the three genera studied are different. Petrodromus (tetradactylus) maintains a relatively low body temperature and metabolic rate, but has the lowest relative evaporative water loss and the highest absolute thermal conductance. These characteristics are correlated with a thermally stable but warm, humid environment, and are not explained by taxonomy. The thermal biology and metabolism of species of the other two genera, Macroscelides and Elephantulus, are interpreted as adaptations to thermally variable, arid environments. Although physiologically well adapted, the thermal and metabolic strategy of Macroscelides (proboscideus) is greatly influenced by its nocturnal behaviour and use of a burrow. The body temperatures and metabolic rates of Elephantulus species are markedly similar, and evaporative water loss varies with water availability in their respective habitats. Species differences are discussed in relation to habitat, behaviour and taxonomy.It is suggested that the common metabolic characteristics of elephant‐shrews were evolved in a stem ancestor, whereas adaptive characters include physiological and behavioural responses to control evaporative water loss and thermal conductance. The metabolic strategy of elephantshrews contributes to their ecological and evolutionary success.