Familiarity and phenotypic similarity influence kin discrimination in the social rodent Octodon degus

To evaluate the two most widely accepted mechanisms of kin recognition, prior association and phenotype matching, we studied kin discrimination in the South American hystricognath rodent Octodon degus. We first assessed differential treatment towards kin during paired encounters in an experimental arena (experiment 1). In addition, we used the habituation technique to investigate odour kin discrimination (experiment 2). In both experiments the relative influence of familiarity and phenotypic similarity were assessed using familiar and unfamiliar siblings, half siblings and genetically unrelated individuals. The results showed that O. degus treat conspecifics differentially as a function of familiarity; young reared apart were equally likely to explore each other independently of genetic relatedness. However, the exploratory behaviour of siblings reared apart and siblings reared together did not differ (experiment 1). On the other hand, degus did discriminate between odours of siblings, half siblings and unrelated individuals reared apart, and between odours of unrelated individuals reared together. Subjects did not discriminate between scents of their siblings reared together with them (experiment 2). These results suggest that familiarity is important in the interaction between animals and in the discrimination of conspecific scents. Nevertheless, our results suggest that phenotypic similarity may also influence social interactions and scent discrimination, although only between close kin, hence possibly influencing communal nesting. We propose that no single mechanism exclusively explains kin discrimination in degus. The prior association recognition mechanism mediated most instances of kin recognition, but phenotype matching is also used in close kin discrimination.