Musculoskeletal mass and shape are correlated with competitive ability in male house mice (Mus musculus)

Intense physical competition between males for mating opportunities is widespread among mammals. In such agonistic encounters, males with combinations of morphological, physiological, and behavioral characters that allow them to dominate an opponent often have greater fitness. However, the specific physical traits associated with competitive ability are poorly understood. Larger body size is often correlated with fitness in mammals. Interestingly, fitness is maximized at intermediate body masses in male house mice (Mus musculus), a species with a polygynous mating system in which males compete physically for access to reproductive resources. Here, we used competition trials in semi-natural, mixed-sex population enclosures to directly measure competitive ability in male house mice based on control of a preferred nesting site. We tested the hypothesis that the musculoskeletal systems of male mice demonstrating high competitive ability are more specialized for competition by comparing the ...