Social behavior is often described as a unified concept, but highly social (group-living) species exhibit distinct social structures and may make different social decisions. Prairie voles (Microtus ochrogaster) are socially monogamous rodents that often reside in extended family groups, and exhibit robust preferences for familiar social partners (same- and opposite-sex) during extended choice tests, although short-term preferences are not known. Mice (Mus musculus) are gregarious and colonial, but in brief laboratory tests of social preference they typically prefer social novelty. This preference for novel vs. familiar peers may represent a species-specific difference in social decision-making between mice and prairie voles. However, the tests used to measure preferences in each species differ markedly in duration and degree of contact, such that the behaviors cannot be directly compared. We assessed whether social preferences for novelty or familiarity differed between mice and prairie voles of both sexes when assessed with matching protocols: the sociability/social preference test (SPT) typically used in mice (short, no direct contact), and the partner preference test (PPT) used in voles (long, direct contact). A subset of voles also underwent a PPT using barriers (long, no direct contact). In the short SPT, behavior did not differ between species. In the longer test, pronounced partner preferences emerged in prairie voles, but mice exhibited no social preferences and rarely huddled. No sex differences were evident in either test. Direct physical contact was required for partner preferences in huddling time in voles, but preference for the partner chamber was evident with or without contact. Both prairie voles and mice are social, but they exhibit important differences in the specificity and extent of their social behavior. While mice are often used to study social approach and other behaviors, voles are a more suitable species for the study of selective social relationships. Consideration of these differences will be important for studies examining the neural mechanisms supporting different kinds of peer social behavior.

The peptide hormone oxytocin (OT) plays an important role in social behaviors, including social bond formation. In different contexts, however, OT is also associated with aggression, social selectivity, and reduced affiliation. Female meadow voles form social preferences for familiar same-sex peers under short, winter-like day lengths in the laboratory, and provide a means of studying affiliation outside the context of reproductive pair bonds. Multiple lines of evidence suggest that the actions of OT in the lateral septum (LS) may decrease affiliative behavior, including greater density of OT receptors in the LS of meadow voles that huddle less. We infused OT into the LS of female meadow voles immediately prior to cohabitation with a social partner to determine its effects on partner preference formation. OT prevented the formation of preferences for the partner female. Co-administration of OT with a specific OT receptor antagonist did not reverse the effect, but co-administration of OT with a specific vasopressin 1a receptor (V1aR) antagonist did, indicating that OT in the LS likely acted through V1aRs to decrease partner preference. Receptor autoradiography revealed dense V1aR binding in the LS of female meadow voles. These results suggest that the LS is a brain region that may be responsible for inhibitory effects of OT administration on affiliation, which will be important to consider in therapeutic administrations of OT.