Meeting Abstract
Animals living in extreme environments must be able to accommodate any associated increased energy demands. High altitude is one such environment that includes stressors such as hypoxia. Most studies have emphasized the max (VO2max) and min (BMR) energy expenditures. VO2max is measured with forced exercise while BMR is measured under conditions rarely measured in nature. However, the effects of normal and voluntary activity are often ignored in controlled laboratory studies using captive animals. To understand the effects of normal and ‘preferred’ activity in caged animal systems, our study examines the costs of voluntary wheel running at both high and low altitude in deer mice (Peromsycus maniculatus). We wondered how voluntary activity might change to accommodate the physiological costs of hypoxia or other physiological parameters. To do this we measured the sustained metabolic rate (SusMR; kJ/day) of mice with and without wheels, wheel running activity and other physiological variables in deer mice both at low altitude and recently (< 4 days) moved to high altitude. We found that the SusMR was 59% higher in mice at high altitude (regardless of whether they had wheels). Likewise, mice with wheels have a SusMR that is 13% higher than mice without wheels (regardless of altitude). However, mice recently introduced to high altitude with wheels ran 13% less and had a VO2max that was 13% lower than mice at low altitude with wheels; thus, there appears to be a trade-off between energy costs and voluntary activity for the mice recently moved to higher altitudes. Previous studies have shown that the deficit between VO2max at low and high altitudes is regained after 8 weeks of acclimation. We will discuss the effects of recent and long-term hypoxia on SusMR as well as other aspects of deer mouse physiology.
