Rank-dependency of major urinary protein excretion in two house mouse subspecies

Chemical communication is important for many social mammals. Scent-related gene clusters have undergone extraordinary expansion in some species, such as the house mouse (Mus musculus). One such family encodes major urinary proteins (MUPs). MUPs can provide recipients with complex information about the signaller and potentially serve as honest signals of social rank. In this study, we examined the development of overall MUP production in two mouse subspecies in the context of establishing their social hierarchy during the critical period between weaning and 100 days of age. We used fraternal pairs as simple social units, where dominant/subordinate ranks were naturally established between two brothers raised together, to test the hypothesis that dominant males of both taxa excrete higher amounts of MUPs in their urine than subordinates. The results were compared to data on ontogeny of steroid hormone levels gathered in the same individuals during an earlier experiment. Higher MUP levels in dominant males were only corroborated in one subspecies (domesticus), whereas musculus males revealed similar MUP quantities irrespective of rank. These results are consistent with the notion that these closely related taxa adopted different strategies for establishing social hierarchy.