Growing up together or apart: Rearing experience effects on opposite-sex sibling discrimination in Chilean brush tailed mouse (Octodon degus)

Kin recognition refers to the discrimination and subsequent behavioral bias toward close relatives. Kin recognition is an important modulator of social interaction. Among relatives, reduced exploration, lower aggressiveness, and decreased inbreeding are typically expected. Two main mechanisms influence kin discrimination: prior association (familiarity) and genetic relatedness. In this study, we investigated kin discrimination between opposite-sex siblings in degus ( Octodon degus ), a diurnal, communally nesting rodent endemic to central Chile. While in this species discrimination among same-sex siblings has been shown to be mainly influenced by rearing experience, it remains unknown whether degus can discriminate their opposite-sex siblings at all, and if so, what mechanisms are at play. We used a cross-fostering protocol to experimentally separate the effects of familiarity and genetic relatedness, producing four groups that combined siblings and non-siblings reared together or apart. Behavior was assessed in two experimental setups: (i) a y-maze to test olfactory preferences and (ii) a dyadic encounter arena to evaluate social interactions. In the y-maze, each experimental subject was simultaneously exposed to one sibling and one non-sibling (stimuli pair, SP), both of the opposite sex. Exploration increased significantly when the subject had no rearing experience with either SP member. Females explored more than males the y-maze. Dyadic encounter experiments showed that rearing experience influenced exploratory and agonistic interactions but not sexual behaviors. Social contact, on the other hand, was more frequent among siblings. Taken together, our results indicate that rearing experience plays a major role in modulating opposite-sex social behaviors in this species.