Maximal metabolic rates during voluntary exercise, forced exercise, and cold exposure in house mice selectively bred for high wheel-running

Abstract

SUMMARY 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(V̇O2max) 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, V̇O2max was measured twice on a motorized treadmill and twice during cold-exposure in a heliox atmosphere (HeO2). Almost all measurements, except heliox V̇O2max, 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 V̇O2max during forced exercise or in heliox, nor in maximal running speeds on the treadmill. However, running speeds and V̇O2max during voluntary exercise were significantly higher in S lines. Nevertheless, S mice never voluntarily achieved the V̇O2max 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.

A strong response to selection on mass-independent maximal metabolic rate without a correlated response in basal metabolic rate

“…Mice selected for higher voluntary running had elevated MMR during voluntary exercise (Rezende et al, 2005), but they did not have higher BMR (Kane et al, 2008). In addition, during forced exercise, neither MMR nor BMR was greater in mice selected for high voluntary running than in controls (Rezende et al, 2005(Rezende et al, , 2009). On the basis of these results, it would be intriguing to see what would happen to MMR and BMR if one selected on the intensity of exercise; that is, which would likely be more similar to our selection for high MMR.…”

“…Lines of mice selected to be high runners ran for more hours per day but not at faster speeds (Garland et al, 2011). Mice selected for higher voluntary running had elevated MMR during voluntary exercise (Rezende et al, 2005), but they did not have higher BMR (Kane et al, 2008). In addition, during forced exercise, neither MMR nor BMR was greater in mice selected for high voluntary running than in controls (Rezende et al, 2005(Rezende et al, , 2009).…”

“…For example, artificial selection can be used to test which characters evolve in response to selection on resting or maximal metabolic rate. Likewise selection on traits, such as running performance, can be used to test whether metabolism evolves as a correlated response (Rezende et al, 2005(Rezende et al, , 2009. While each experiment is specific to the animals being studied, the collective information from numerous studies can be used to explore whether phenotypic and genetic integration is ubiquitous, consistent or inconsistent across various species, populations or other units of interest.…”

Are Voluntary Wheel Running and Open-Field Behavior Correlated in Mice? Different Answers from Comparative and Artificial Selection Approaches

“…Duman et al (2008) speculated that reduced locomotion in the open-field that was possibly related to immediate fatigue after running (see also Fuss et al 2010). This seems unlikely to us, however, as even our HR mice do not run voluntarily on wheels at speeds that exceed their maximal aerobic capacity Rezende et al 2005), nor do they show obvious signs of fatigue during or following wheel running (Meek et al 2009;personal observations). Alternatively, voluntary wheel running induces a significant elevation in circulating corticosterone in both HR and C mice (Girard and Garland 2002) and in C57BL/ 6N mice (Droste et al 2003).…”

Erythropoietin elevates but not voluntary wheel running in mice

“…3074; Mallinckrodt Baker, Deventer, Holland) diluted in Drabkin's reagent in the following concentrations: 0.0, 5.5, 13.8 and 17.5g100ml -1 . The mean absorbance of the duplicate samples was used to calculate the [Hb].Forced exercise on a treadmill was used to measure V O2,max (Hayes and Chappell, 1990;Chappell et al, 2003;Rezende et al, 2005;Rezende et al, 2006a). The treadmill was inclined at a 15deg.…”