Field and Maximal Metabolic Rates of Deer Mice (Peromyscus maniculatus) at Low and High Altitudes

Abstract

The field metabolic rates (FMRs) of deer mice (Peromyscus maniculatus) were studied at low (1,230 m) and high (3,800 m) altitudes by means of the doubly labeled water (DLW) technique. Maximal rate of oxygen consumption ($\dot{V}O_{2}max$) during acute cold exposure was also measured The ratio of FMR: Vozmax was used as an indicator of the potential for metabolic constraints. Mean FMR was 57% greater at high altitude than at low altitude. Despite theoretical predictions and limited previous evidence that $\dot{V}O_{2}max$ declines with altitude, mean $\dot{V}O_{2}max$ did not differ between low and high altitudes. $\dot{V}O_{2}$ was sustainable at $\dot{V}O_{2}max$ for at least 2 h. At high altitude, mean FMR was 57% of mean $\dot{V}O_{2}max$, while at low altitude, mean FMR was only 36% of mean $\dot{V}O_{2}max$. Particularly during their active periods, deer mice at high altitude operate closer to the maximal $\dot{V}O_{2}$ that is sustainable than do deer mice at low altitude.