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Selection for high voluntary wheel-running increases speed and intermittency in house mice (Mus domesticus)

I. Girard^*, M. W. McAleer, J. S. Rhodes and T. Garland, Jr.

Department of Zoology, 430 Lincoln Drive, University of Wisconsin-Madison, Madison, WI 53706, USA
Present address: Department of Biology, University of California Riverside, Riverside, CA 92521-0427, USA

View larger version (21K): [in a new window]   Fig. 1. Circadian pattern of wheel-running on day 6 of a 6-day exposure to wheels in selection (filled circles) and control (open circles) lines of house mice (females) included in a videotape microanalysis of wheel-running. Values are means ± S.E.M. The graph shows the number of revolutions for each 20-min period as collected by an automated system in 1-min bins.

View larger version (27K): [in a new window]   Fig. 2. Example of wheel-running as collected by the automated system for a selection-line female (filled circles) and a control female (open circles) during an hour of peak wheel-running activity and the 5-min observation period used for videotape microanalysis (filled bars). The four deceleration events from the wheel of the selection-line female suggest that she may have stopped running during these times, although the automated system recorded continuous activity over the hour. The wheel of the control-line animal clearly stopped rotating at least twice during this hour.

View larger version (14K): [in a new window]   Fig. 3. Selection-line females (filled circles) ran bouts that were shorter and more frequent than those of control females (open circles). In both groups, the frequency and duration of running bouts show a strong negative relationship. The dashed line represents the maximum possible combination of bout frequency and duration if pause durations approach zero (individual points can lie above this line because of measurement error).

View larger version (20K): [in a new window]   Fig. 4. Diagrammatic depiction of average patterns of intermittent wheel-running for selection-line (top) and control (bottom) female mice over the 5-min videotaped observation: open columns represent periods of running, filled columns represent pause periods of coasting and hatched columns represent periods when the mouse had exited from the wheel.

View larger version (29K): [in a new window]   Fig. 5. Relationships between characteristics of wheel-running as measured during videotape microanalysis and the total number of revolutions over day 6 as recorded by an automated system. These data reflect the original selection criterion. Filled circles, selection-line mice; open circles, control mice. Note that the abscissa for bout speed is different from the others, reflecting its narrower range of variation on the logarithmic scale. Bout speed is measured in revs min–1, bout duration in s, bout frequency in min–1 and interbout pause in s.

View larger version (20K): [in a new window]   Fig. 6. Wheel-running speeds are greater in selection-line females (filled symbols) than in control females (open symbols) when measured by direct observation during videotaping (A; mean bout speed, N=41) or when estimated for all females of generation 23 using computer-recorded data (B; maximum speed in any 1-min interval, N=268). In B, squares designate videotaped animals. In some selection-line females, mean bout speed and maximum speed in any 1-min interval are near or above the predicted maximal aerobic speed [predicted for a 28 g animal from Fig. 6 of Koteja et al. (1999)] on a running wheel (dashed line).