Regularity, variability, and individuality: urine marking patterns of male mice toward stimuli representing varying degrees of kinship.

Successful social interactions require the identification of conspecifics and their traits. Often, individuals do not directly interact with conspecifics, but rather with their secretions. Among bodily secretions, urine plays a primary role in social communication across species. Urine provides a wealth of social information, and accordingly, several species, including mice, use it to advertise and mark territories. Here, we asked if kinship relations are reflected by the subject's marking patterns. Specifically, we studied counter-marking patterns of outbred ICR male mice following presentation of urinary cues from conspecifics with varying degrees of kinship. Examination of more than 1000 individual marking patterns from 10 mice reveals a high degree of variability. Variability is apparent across different mice and across single marking bouts of any given individual. Yet, we identify consistent effects of stimulus kinship, and, somewhat unexpectedly, even more robust differences among individuals. Individual-specific marking patterns are also evident in an empty arena, prior to the introduction of an external stimulus. Stimulus presentation gives rise to further changes in marking patterns, reflecting the relationship between the subject and donor mice. Notably, while stimuli representing highly distinct kinship relations induce robust differences at the population level, finer distinctions, including discrimination of same-strain conspecifics and self-urine, are only displayed by a subset of mice. Thus, while counter marking patterns are determined by a variety of factors, some of which cannot be easily controlled or measured, they ultimately reflect the identity of the marker and the kinship relation with the stimulus donor.