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First published online June 6, 2005
Journal of Experimental Biology 208, 2447-2458 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01631
Maximal metabolic rates during voluntary exercise, forced exercise, and cold exposure in house mice selectively bred for high wheel-running
Department of Biology, University of California, Riverside, California 92521, USA
* Author for correspondence (e-mail: enrico.rezende{at}email.ucr.edu)
Accepted 31 March 2005
Selective breeding for high wheel-running activity has generated four lines
of laboratory house mice (S lines) that run about 170% more than their control
counterparts (C lines) on a daily basis, mostly because they run faster. We
tested whether maximum aerobic metabolic rates
(
O2max) have
evolved in concert with wheel-running, using 48 females from generation 35.
Voluntary activity and metabolic rates were measured on days 5+6 of wheel
access (mimicking conditions during selection), using wheels enclosed in
metabolic chambers. Following this,
O2max was
measured twice on a motorized treadmill and twice during cold-exposure in a
heliox atmosphere (HeO2). Almost all measurements, except heliox
O2max, were
significantly repeatable. After accounting for differences in body mass
(S<C) and variation in age at testing, S and C did not differ in
O2max during
forced exercise or in heliox, nor in maximal running speeds on the treadmill.
However, running speeds and
O2max during
voluntary exercise were significantly higher in S lines. Nevertheless, S mice
never voluntarily achieved the
O2max elicited
during their forced treadmill trials, suggesting that aerobic capacity per
se is not limiting the evolution of even higher wheel-running speeds in
these lines. Our results support the hypothesis that S mice have genetically
higher motivation for wheel-running and they demonstrate that behavior can
sometimes evolve independently of performance capacities. We also discuss the
possible importance of domestication as a confounding factor to extrapolate
results from this animal model to natural populations.
Key words: artificial selection, exercise, experimental evolution, locomotor activity, maximum oxygen consumption, running performance, thermogenesis, mouse
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