Scaling of Energy Metabolism and Evaporative Water Loss in Heteromyid Rodents

Oxygen consumption (V̇o2), evaporative water loss (ṁwe), and body temperature (Tb) of 117 individuals of 13 species of heteromyid rodents were determined at ambient air temperatures (Ta) of 5, 15, 25, and 35 C; the 13 species encompass all five genera in the family Heteromyidae, cover the range in habitat distribution, and vary in body mass from 8 to 130 g. The relationship between V̇o2 and Ta generally follows the Scholander model in the 13 species, although the three nonxeric species (Heteromys desmarestianus, Liomys irroratus, L. salvini) exhibit a thermoneutral point, not a zone, within the Ta's measured. Thermal conductances, ṁwe, and Tb do not vary between Ta's of 5-25 C but do increase at 35 C, except for ṁwe in three Perognathus spp. The allometric relationships of mass-specific V̇o2, ṁwe, and thermal conductances to body mass have similar slopes relative to other eutherian mammals; however, the relationships in heteromyids are depressed below those of other eutherians at all temperatures. In general, these physiological variables are depressed in the semixeric-and xeric-dwelling heteromyid species but are similar to those predicted for other eutherians of the same body mass in the three nonxeric heteromyid species. The reduced levels of metabolism and evaporative water loss are considered adaptive for energy and water conservation linked to the family's dietary specialism, granivory.