Meeting Abstract

47.5  Saturday, Jan. 5  Forced and voluntary running costs and morphological correlates with performance in deer mice VAN DOLAH, K.M.*; CHAPPELL, M.A.; Univ. of California, Riverside; Univ. of California, Riverside kyle-vandolah@earthlink.net

Most of what is known about costs of running come from forced exercise at constant speeds for long durations, which is very different from the intermittent locomotion used by animals. To determine if there are differences between the energy costs, we examined the cost of transport (COT) in forced and voluntary running, maximal aerobic capacity (VO_2max), and organ and muscle mass in deer mice (Peromyscus maniculatus). Mice were tested in an enclosed running wheel respirometer that allowed measurement of oxygen consumption (VO₂) and running speed in freely behaving animals. For each individual we determined the slope (iCOT) and intercept of regressions of (VO₂) versus speed. These were compared to corresponding values measured during forced exercise on a motorized treadmill. We predicted that costs for voluntary exercise would be lower than forced exercise because of reduced stress and potentially, a preference for more economical speeds. However, no significant difference was found between the two measures of iCOT or intercept. We also measured basal metabolic rate (BMR), maximal VO₂ (VO_2max), and organ masses. BMR was correlated with small intestine mass. Average Voluntary VO₂ was correlated with ovary/testis and liver mass, and average forced VO₂ was correlated with heart, spleen and reproductive organ mass. VO_2max correlated with heart mass. We found no correlation between organ mass and any of the measures of behavior (e.g. total running time and total running distance) during the voluntary running trial.