Thermoregulation, metabolism, and water economy in the golden mouse ( Ochrotomys nuttalli)

Abstract

Abstract 1. Thermoregulation, metabolism, and water relationships in the golden mouse ( Ochrotomys nuttalli ) were studied using two groups of animals (“field”-in captivity less than a month; “laboratory”-in captivity over a year). 2. Mean T b of field and laboratory groups combined was 36·38°C and was independent of T a between 5 and 35°C. Extreme lethargy reduced heat stress at high T a . 3. The thermal neutral zone, BMR, and conductance of field subjects were 29·5–36°C, 1·39 cm 3 /g-hr, and 0·23 cm 3 /g-hr/°C, respectively. 4. Values of various parameters of water economy in field individuals (unless otherwise noted) were: normal water consumption, 0·233 ml/g-day; weight loss after 2 days water deprivation, 22%; mean pulmocutaneous water loss between 5 and 33°C, 2·7 mg/g-hr; minimum H 2 O/O 2 ratio, 1·47 (laboratory group); mean urine production, 0·061 ml/g-day on ad libitum water to 0·024 ml/g-day after 2 days water deprivation; mean urine concentration of normally hydrated mice, 1386 mOsm/kg, increasing to 2686 mOsm/kg after 2 days without water; maximum urine/serum ratio, 9·5; mean normal and maximum fecal water content, 56 and 48%, respectively. 5. Compared with mice of the related genus Peromyscus, Ochrotomys has comparable thermoregulatory ability, low BMR, high conductance, and water relationships generally resembling species and subspecies from mesic habitats. 6. The low BMR and the tendency to become lethargic at high T a may be adaptive in reducing heat stress in exposed nests during high summer daytime temperatures. The relatively high conductance, tendency to maintain normal T b at low T a , and lack of specialized water conservation mechanisms may play a significant role in limiting the golden mouse to relatively moist forest environments in southern United States.