Many animals become more motivated to interact after a period of isolation. This phenomenon may involve general drives, e.g. for social touch or companionship, as well as drives that are specific to particular peers, and which ultimately serve to reestablish relationships between the individuals. Female degus are known to be affiliative with multiple other individuals, including unrelated and unfamiliar conspecifics, offering an opportunity to study social motivation independent from exclusive pair-bonds or overt, same-sex competition. We attempted to disentangle factors driving peer interaction by examining reunion behavior across several social isolation and separation manipulations. High levels of interaction were observed between adult females who had been separated even without isolation, revealing a drive to re-establish relationships with specific peers. The content of separation-only reunions differed from isolation, with the latter involving more early-session interaction, higher levels of allogrooming before rear-sniffing, and a higher ratio of chitter vocalizations. To assess whether post-isolation behavior was related to stress, we examined reunions following a non-social (footshock) stressor. Like isolation, footshock increased early-session interactions, but did not increase allogrooming before rear-sniffing or chittering, as compared with controls. To test whether separation-only reunion behavior shared qualities with relationship formation, we also examined reunions of new (stranger) dyads. Strangers exhibited higher levels of interaction than cagemates, with particularly high levels of late-session rear-sniffing. Like separation-only reunions, strangers showed more non-chitter vocalizations and lower levels of allogrooming before rear-sniffing. Across experiments, an exploratory clustering method was used to identify vocalizations that differed between conditions. This yielded promising leads for future investigation, including a chaff-type syllable that may have been more common during relationship renewal. Overall, results are consistent with the hypothesis that female degu reunions are supported by both general and peer-stimulus specific drives, expressed through the structure of physical and vocal interactions over time.

AbstractA full understanding of a species’ sociality requires knowledge of their specific social motivations. Following social isolation, animals may show general interest in companionship as a buffer for stress or loneliness, but may also be driven to re-establish expectations and dyadic roles with individuals they had been previously separated from. By deconstructing social behavior across experimental manipulations, it may become possible to disentangle these motivational factors. Physical and vocal interactions were recorded from adult female degu dyads during a series of 20 minute reunion sessions across four experiments. Experiments 1 and 2 found that degu interactions increased following isolation, but also increased after dyads were separated without isolation from other conspecifics. Isolation resulted in more early-session interactions, higher allogrooming before rear-sniffing, and a higher ratio of chitter to non-chitter vocalizations. Experiment 3 showed that a non-social, footshock stressor selectively increased early-session interaction, and Experiment 4 revealed high interaction rates between strangers, with more non-chitter vocalizations and late-session rear-sniffing, and reduced pre-rear-sniff allogrooming. A novel, repeated-k-means clustering approach helped to further specify differences in vocalizations between conditions; e.g., “chaff”-type syllables were more common when relationships were new or potentially being renewed. Results suggest that degus are motivated to establish or re-establish expectations with one-another, and these interactions can differ from those associated with the stress of isolation.