Physiological evidence for genetically mediated sibling recognition in mice.

The kin selection theory predicts that individuals would behave differently toward one another, depending on their genetic relatedness. Kin discrimination has been demonstrated in mice from social behavior, and previous familiarity, as well as familiarity with the partner's phenotype, has been postulated to represent proximate mechanisms. It has already been demonstrated that siblings' reunion resulted in a decrease in pain sensitivity that is mediated by endogenous opioids. In this study, using a cross-transferring design, it is shown that genetic relatedness with the male partner, independently of postnatal association, is responsible for changes in nociceptive threshold. Conversely, previous association till weaning has no effect on pain sensitivity. These data suggest that endogenous opioids activity and social behavior represent indices of different processes: the recognition of related animals and the discrimination of familiar (and also usually related) subjects, respectively.