Dominance rank inference in mice via chemosensation

Social dominance hierarchies enable efficient resource allocation and conflict avoidance in animal communities.¹ Individuals can determine their relative status by tracking previous conflict outcomes, as seen in aggression training² and the winner effect,³^,⁴ where successive wins increase the likelihood of future victories. Repeated optogenetic stimulation of the dorsomedial prefrontal cortex (dmPFC) results in lasting rank increases,⁵ suggesting that social rank is derived as a statistic of past outcomes. However, relative rank could be assessed more efficiently by incorporating information about an opponent's dominance status. Pheromone signals, such as darcin, are enriched in the urine of dominant individuals,⁶^,⁷^,⁸^,⁹ suggesting that hierarchical behavior may integrate information about both own and opponent rank. Although prior studies have explored the learning and neural representation of own rank,⁵^,¹⁰^,¹¹ how opponent rank is detected and encoded remains unclear. Here, we address this question in male mice using a tube test assay. We show that stable hierarchies do not rely on fixed behavioral traits and that mice can infer the rank of unfamiliar opponents by detecting scalable chemosensory rank cues. Sensory ablation experiments reveal that both olfactory and vomeronasal cues are sufficient for rank assessment. Male mice thus use chemosensory signals to infer dominance status during social interactions.