Field and Laboratory Studies of Water Metabolism in Sminthopsis Crassicaudata (Marsupialia : Dasyuridae).

S. crassicaudata is a small insectivorous marsupial which inhabits xeric to mesic habitats in southern Australia. Field and laboratory studies of the water metabolism of this species were carried out to determine the extent to which physiological adaptations contribute to its ability to inhabit arid environments. S. crassicaudata can subsist without drinking water when fed a diet of insects; this independence is made possible primarily by the high water content of the food, and not by physiological restriction of the rate of water usage as in many granivorous desert-dwelling rodents. Mean daily water turnover rates in the laboratory were 50-75% body water, and in the field were 110-190% body water. These high rates are interpreted in terms of lack of selection for water conservation in an animal subsisting on a moist diet; in such animals water turnover rate primarily reflects metabolic rate. These conclusions were supported by comparative studies of the water and energy metabolism of Planigale maculata. This species withstood water deprivation better than did S. crassicaudata, even though it inhabits much wetter environments; this was almost certainly due to its lower metabolic rate and, therefore, lower water turnover rate. These studies suggest that use of insect food by a desert-dwelling small mammal virtually removes the physiological problem of water conservation.