Scent mark signal investment predicts fight dynamics in house mice

Abstract Signals mediate competitive interactions by allowing rival assessment, yet are often energetically expensive to produce. Individuals face tradeoffs when deciding when and where to signal, such that over or under-investing in signaling effort can be costly. One of the key mechanisms maintaining signal reliability is via social costs. While the social costs of over-signaling are well-known, the social costs of under-signaling are underexplored, particularly for dynamic signals. In this study we investigate a dynamic and olfactory-mediated signaling system that is ubiquitous among mammals: scent marking. Male house mice territorially scent mark their environment with metabolically costly urine marks. While competitive male mice are thought to deposit abundant scent marks in the environment, we recently identified a cohort of low-marking males that win fights. Whereas there are clear energetic costs to investing in urine signals in mice, we hypothesized that there may be social costs imposed on individuals who under-invest in signaling. Here we find that scent mark investment predicts fight dynamics. Despite fight outcome being unambiguous, aggressive intensity varies considerably across trials. Males that produce fewer scent marks 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 signaling winners. We therefore find evidence for rival assessment of scent marks as well as social costs to under-signaling, which supports existing hypotheses for the importance of social punishment in maintaining optimal signaling equilibria. Our results further highlight the possibility of diverse signaling strategies in house mice.