A disparity between locomotor economy and territory-holding ability in male house mice.

Both economical locomotion and physical fighting are important performance traits to many species because of their direct influence on components of Darwinian fitness. Locomotion represents a substantial portion of the total daily energy budget of many animals. Fighting performance often determines individual reproductive fitness through the means of resource control, social dominance and access to mates. However, phenotypic traits that improve either locomotor economy or fighting ability may diminish performance in the other. Here, we tested for a predicted disparity between locomotor economy and competitive ability in wild-derived house mice (Mus musculus). We used 8 week social competition trials in semi-natural enclosures to directly measure male competitive ability through territorial control and female occupancy within territories. We also measured oxygen consumption during locomotion for each mouse using running trials in an enclosed treadmill and open-flow respirometry. Our results show that territory-holding males have higher absolute and mass-specific oxygen consumption when running (i.e. reduced locomotor economy) compared with males that do not control territories. This relationship was present both before and after 8 week competition trials in semi-natural enclosures. This disparity between physical competitive ability and economical locomotion may impose viability costs on males in species for which competition over mates is common and may constrain the evolution of behavioral and phenotypic diversity, particularly in natural settings with environmental and resource variability.