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First published online October 7, 2004
Journal of Experimental Biology 207, 3839-3854 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01213
Voluntary running in deer mice: speed, distance, energy costs and temperature effects
Department of Biology, University of California, Riverside, CA 92521, USA
* Author for correspondence (e-mail: chappell{at}citrus.ucr.edu)
Accepted 26 July 2004
The energetics of terrestrial locomotion are of considerable interest to ecologists and physiologists, but nearly all of our current knowledge comes from animals undergoing forced exercise. To explore patterns of energy use and behavior during voluntary exercise, we developed methods allowing nearly continuous measurements of metabolic rates in freely behaving small mammals, with high temporal resolution over periods of several days. We used this approach to examine relationships between ambient temperature (Ta), locomotor behavior and energy costs in the deer mouse, a small mammal that routinely encounters a large range of temperatures in its natural habitat. We tested for individual consistency in running behavior and metabolic traits, and determined how locomotor costs vary with speed and Ta. Because of the importance of thermoregulatory costs in small mammals, we checked for substitution of exercise heat for thermostatic heat production at Ta below the thermal neutral zone and determined the fraction of the daily energy budget comprising exercise costs.
Locomotor behavior was highly variable among individuals but had high
repeatability, at least over short intervals. We found few temperature-related
changes in speed or distance run, but Ta strongly affected
energy costs. Partial substitution of exercise heat for thermogenic heat
occurred at low Ta. This reduced energy expenditure during
low-temperature running by 23–37%, but running costs comprised a fairly
minor fraction of the energy budget, so the daily energy savings via
substitution were much smaller. Deer mice did not adjust running speed to
maximize metabolic economy, as they seldom used the high speeds that provide
the lowest cost of transport. The highest voluntary speeds (4–5 km
h-1) were almost always below the predicted maximal aerobic speed,
and were much less than the species' maximal sprint speed. Maximum voluntarily
attained rates of oxygen consumption
(
O2) were
highest at low Ta, but rarely approached maximal
O2 during forced
treadmill exercise. Mean respiratory exchange ratios coincident with maximal
voluntary O2
increased slightly as Ta declined, but were always below
1.0 (another indication that metabolic rate was less than the aerobic
maximum). Individuals with high running performance (cumulative distance and
running time) had high resting metabolism, which suggests a cost of having
high capacity or propensity for activity.
Key words: aerobic capacity, deer mouse, exercise, locomotion, maximal oxygen consumption, metabolism, Peromyscus maniculatus, wheel-running
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