Juvenile social relationships reflect adult patterns of behavior in wild geladas.

Unlike many mammals, primates spend much of their lives as reproductively-immature juveniles. During the juvenile period, they develop social relationships and physical skills that both facilitate survival to adulthood and impact adult fitness. In this study, we use 2 years of observational data to examine the development of these skills across the juvenile period in a wild cercopithecine primate, the gelada (Theropithecus gelada). As adults, male and female geladas require different skills to be successful; we therefore expected sex differences in social behavior and partner choice during the juvenile period to already reflect these sex-specific trajectories. For example, males, who disperse at puberty and ultimately must challenge other adult males for access to mates, should invest in high-energy play-fighting with other males to develop fighting and rival assessment skills. In contrast, philopatric females, who remain with their close kin throughout their lives, should invest more in forming less-physical and more-social bonds with other females within their group. As predicted, sex differences that foreshadowed sex-specific adult roles were apparent in play rates, the average number of play partners per individual, grooming partner types and social partner preferences. Males played more and had more play partners than same-age females. Males also groomed more often with individuals from outside their natal group than females, although no sex difference was observed in either grooming rates or number of grooming partners per individual. Females stopped playing earlier than males, and instead invested in grooming relationships with close relatives. Additionally, we found that individual play and grooming rates were temporally consistent for both males and females (i.e., from one year to the next year), suggesting that individuals exhibit stable behavioral phenotypes. We conclude by discussing how early life in geladas may shape adult behavior and reproductive strategies.