Analysis of the disruption of maternal social bonds in Octodon degus: Separation distress in restricted reunion tests

Octodon degus is a social caviomorph species that exhibits strong social bonds and robust distress responses to maternal separation. To understand the impact of early social isolation on social motivation, we investigated how social isolation during infancy, associated with repeated restricted interactions with mother and siblings, altered social motivation in young degus. In Experiment 1, three treatments were compared: complete isolation (ISOLATED group), nearly complete isolation, with daily half hour partition-restricted reunions with the mother and siblings (RESTRICTED group), and social-housing with the mother and siblings (FAMILY group). After 10 days of treatment, all subjects underwent a 5-day choice test between mothers and unfamiliar females. During the treatment period, the RESTRICTED animals emitted more isolation calls and spent more time close to the partition that separated them from mothers than ISOLATED animals. During the first social-choice day, FAMILY reared animals showed a preference for the mother for a few minutes, while the RESTRICTED animals preferred the mother for the whole session. Totally ISOLATED pups exhibited no social preferences. Since during successive testing periods the isolation calls decreased over the days, in Experiment 2 we investigated whether this decline was related to age or habituation to testing procedures. Animals were observed during a single exposure to isolation (ISOLATED) or restricted-reunion (RESTRICTED) at PND 21 and 31. The decrease of vocalizations was due to an age-effect. The findings clarify the nature of social bonds in degus