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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

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Voluntary running in deer mice: speed, distance, energy costs and temperature effects

Mark A. Chappell^*, Theodore Garland, Jr, Enrico L. Rezende and Fernando R. Gomes

Department of Biology, University of California, Riverside, CA 92521, USA

View larger version (43K): [in a new window]   Fig. 1. Schematic diagram of the running wheel enclosure. A, wheel axle (attached to the back side of the housing); F, fan; T, recirculation tube; C, mouse cage; D, access door; E, wheel entry tube; P, waste pan; G, wheel speed generator; S, space filler. Not shown: food hopper, drinking tube, air access ports, other space fillers in corners of wheel housing and around mouse cage. The internal volume (without cage, bedding, and food) is approximately 22.7 liters.

View larger version (34K): [in a new window]   Fig. 2. (A) Oxygen consumption (top) and wheel speed (bottom) in an 18.7 g female deer mouse voluntarily exercising at 3°C. For these analyses we used absolute values of wheel speed, ignoring changes in the direction of wheel rotation. (B) First 30 min of running, showing rapid speed changes. (C) Decline in autocorrelation over increasing inter-sample intervals. The r2 values are between samples separated by 1–200 sample intervals (1.5 s), repeated for all 8400 samples during the period indicated by the dark bar in part A (see text). Autocorrelation was negligible for intervals >150 s.

View larger version (21K): [in a new window]   Fig. 3. The relationship between voluntary running speed and oxygen consumption (O2) in a 21.5 g deer mouse tested at an ambient temperature of 25°C. This female ran 18.9 km during the 24 h measurement period. Data points are 60 s averages separated from other points by at least 3 min to avoid autocorrelation biases (Fig. 2). Data for speeds less than 0.034 km h-1 (0.5 r.p.m.) were not used (see text). The broken line is equal to this animal's maximal O2 during forced treadmill exercise (4.304 ml min-1) and the estimated maximum aerobic speed is 4.8 km h-1.

View larger version (18K): [in a new window]   Fig. 4. (A) Minimal resting metabolism (diamonds, 5 min averages; open circles, 30 min averages), average daily energy use (squares), and highest oxygen consumption (filled circles; 1 min average) at three ambient temperatures. The solid diamond in the upper left indicates the maximal O2 (1 min average) during forced treadmill exercise at room temperature. Values are means ± S.D. (for N, see text). (B) Averaged least-squares regression lines for animals of standard mass (22.2 g) for the relationship between running speed and oxygen consumption. The rightmost end of each regression line indicates the mean maximum instantaneous running speed for that temperature and the circle indicates the mean maximum 1 min average (neither was significantly affected by temperature). Arrows indicate the estimated O2 at the highest attained instantaneous running speed of about 5 km h-1.

View larger version (26K): [in a new window]   Fig. 5. The distribution of voluntary running speeds in deer mice tested at different ambient temperatures (Ta), expressed as time spent (A) and distance traveled (B) at different speeds. Data are 1 min averages, with different points from each animal separated by at least 3 min (see text). The same 32 animals were tested at each Ta, although some individuals ran very little at particular Ta and the number of data points varied among individuals. Downward-pointing arrows (in A) indicate the mean running speed for each Ta, calculated as (cumulative distance/cumulative run) time in 24 h (Table 4). The bin size was 0.068 km h-1 (1 r.p.m. of wheel rotation). For clarity, speeds under 0.068 km h-1 are not shown.

View larger version (17K): [in a new window]   Fig. 6. The distribution of oxygen consumption (O2) during voluntary wheel-running in 32 deer mice tested at different ambient temperatures (Ta). Data are 1 min averages, with different points from each animal separated by 3 min (see text). The same animals were tested at each Ta (variation in sample sizes reflects slight differences in the number of data points in each sample period, and in data lost due to equipment problems). All O2 values were adjusted to the mean body mass of 22.2 g using a scaling factor of mass0.79 (see text). Downward-pointing arrows indicate the treadmill-elicited maximum O2 (O2max) for a 22.2 g mouse (4.2 ml O2 min-1) and the associated percentage is the fraction of data exceeding O2max. The bin size was 0.1 ml O2 min-1.