Scent mark signal investment predicts fight dynamics in house mice.

Signals mediate competitive interactions by allowing rival assessment, yet are often energetically expensive to produce. One of the key mechanisms maintaining signal reliability is social costs. While the social costs of over-signalling are well known, the social costs of under-signalling are underexplored, particularly for dynamic signals. In this study, we investigate a dynamic and olfactory-mediated signalling system that is ubiquitous among mammals: scent marking. Male house mice territorially scent mark their environment with metabolically costly urine marks. Competitive male mice are thought to deposit abundant scent marks in the environment. However, we recently identified a cohort of low-marking males that win fights. We hypothesized that there may be social costs imposed on individuals who under-invest in signalling. Here we find that scent mark investment predicts fight dynamics. Winning males that produce fewer scent marks prior to a fight engage in more intense fights that take longer to resolve. This effect appears to be driven by an unwillingness among losers to acquiesce to weakly signalling winners. We, therefore, find evidence for rival assessment of scent marks as well as social costs to under-signalling. This supports existing hypotheses for the importance of social punishment in maintaining optimal signalling equilibria. Our results further highlight the possibility of diverse signalling strategies in house mice.

Sex-specific competitive social feedback amplifies the role of early life contingency in male mice.

Contingency (or 'luck') in early life plays an important role in shaping individuals' development. When individuals live within larger societies, social experiences may cause the importance of early contingencies to be magnified or dampened. Here we test the hypothesis that competition magnifies the importance of early contingency in a sex-specific manner by comparing the developmental trajectories of genetically identical, free-living mice who either experienced high levels of territorial competition (males) or did not (females). We show that male territoriality results in a competitive feedback loop that magnifies the importance of early contingency and pushes individuals onto divergent, self-reinforcing life trajectories, while the same process appears absent in females. Our results indicate that the strength of sexual selection may be self-limiting, as within-sex competition increases the importance of early life contingency, thereby reducing the ability of selection to lead to evolution. They also demonstrate the potential for contingency to lead to dramatic differences in life outcomes, even in the absence of any underlying differences in ability ('merit').