Scent marking increases male reproductive success in wild house mice

Scent marking is often assumed to be a secondary sexual trait that increases malesʹ mating and reproductive success, although direct evidence for this hypothesis is lacking. We conducted a study with wild-derived house mice, Mus musculus musculus, to test whether scent marking increases malesʹ reproductive success when females can freely choose between two territorial males. We also experimentally manipulated malesʹ competitive scent marking by exchanging scent-marked tiles between the neighbouring malesʹ territories (intrusion treatment) or relocating malesʹ tiles within their own territory (control). Experimental animals were tested twice and we examined whether individual males were consistent in their marking. We found that males marked more in the intrusion treatment than controls and more at shared territorial borders than elsewhere. We found high day-to-day variation in most individualsʹ scent marking, and yet the sum of individualsʹ scent marking was consistent over time and across different social conditions. Genetic paternity analyses revealed that malesʹ scent marking significantly increased their reproductive success in both the intrusion treatment and the controls. Surprisingly, however, female social preference was not positively correlated with male scent marking. These results provide direct evidence that scent marking increases malesʹ reproductive success when females can choose their mates, even though it did not increase femalesʹ social preferences.