Temperature regulation and water economy in desert wolves

Abstract

The wolf, Canis lupus, inhabits deserts at the margins of its broad circumpolar, holarctic range. The wolf subspecies C. l. pallipes (adult body mass 18-22 kg) inhabits arid areas in Israel. Other desert-dwelling canids of similar size reduce their internal heat load through low metabolic rate, but must drink water to survive. To ascertain whether desert wolves behave similarly we measured metabolic rate and evaporative water loss in three hand-reared female wolves under controlled conditions, at ambient temperatures between 0 and 40°C. Using tritiated water, we also measured their total body water and water turnover rates while they were kept in a 0·16 ha outdoor enclosure with shade and water available ad lib. The wolves had a wide thermal-neutral zone which included all test ambient temperatures. Mean standard metabolic rate was 1·20 W·kg -1 in winter and 1·59 W kg -1 in summer; winter and summer standard metabolic rates were respectively, 33·6% and 12·15% lower than predicted allometrically. Evaporative water loss was significantly higher in summer than in winter. Total body water averaged 68% of body mass in both seasons, but mean water turnover rate was significantly higher in summer (97·52 ml·kg -1·day -1) than in winter (27·45 ml · kg -1 · day -1). After 21 h of water deprivation in late summer, wolves lost 11·8% of their initial body mass. They made up 44% of their water deficit in their first post-dehydration drink and the rest over 24 h. Morphological examination of kidneys from 2 road-killed males indicated no extraordinary renal concentrating ability. The data suggests that wolves must drink to meet the physiological challenge posed by the hot desert climate.