Altitudinal and seasonal effects on aerobic metabolism of deer mice

Summary

I compared the maximal aerobic metabolic rates ($\dot V_{O_2 \max }$), field metabolic rates (FMR), aerobic reserves ($\dot V_{O_2 \max }$-FMR), and basal metabolic rates (BMR) of wild and recently captured deer mice from low (440 m) and high (3800 m) altitudes. To separate the effects of the thermal environment from other altitudinal effects, I examined mice from different altitudes, but similar thermal environments (i.e., summer mice from high altitude and winter mice from low altitude). When the thermal environment was similar,$\dot V_{O_2 \max }$, FMR, and aerobic reserve of low and high altitude mice did not differ, but BMR was significantly higher at high altitude. Thus, in the absence of thermal differences, altitude had only minor effects on the aerobic metabolism of wild or recently captured deer mice.

At low altitude, there was significant seasonal variation in$\dot V_{O_2 \max }$, FMR, and aerobic reserve, but not BMR. BMR was correlated with$\dot V_{O_2 \max }$, but not with FMR. The significant positive correlation of BMR with$\dot V_{O_2 \max }$ indicates a cost of high$\dot V_{O_2 \max }$, because higher BMR increases food requirements and energy use during periods of thermoneutral conditions.