Female guinea pigs prefer familiar opposite-sex individuals but not familiar same-sex peers

While some species show a preference for familiar individuals when choosing a social or sexual partner, this tendency is not universal and varies across species. However, the association between partner preference and social system is still not clear, and partner preference needs to be studied in species with different social systems from those already studied. Here we evaluated familiarity preference in nonreproductive (same-sex) and reproductive (opposite-sex) social contexts in female guinea pigs, Cavia porcellus , a species that forms stable groups of two to three females and one male. We used a three-chamber apparatus that allowed the focal females to freely interact and choose between a familiar or novel individual or to remain in a solitary space. Females showed a strong preference for social over nonsocial chambers, indicating a preference for a social companion. Females also exhibited a clear preference for familiar males but exhibited no marked preference between familiar or novel females, suggesting context-dependence preference. This result is consistent with familiarity preference in other species of rodents exhibiting stable social groups, indicating that familiarity is key for the stability of social groups. Our study provides key evidence of opposite-sex partner preference in one Ctenohystrica rodent species and demonstrates partner preference in a mate (opposite-sex) but not a peer (same-sex) context, a novel finding among rodent species.