Caitlin Barale, ID# 26907
LEAKEY FOUNDATION FINAL GRANT REPORT Summary of results My dissertation research focused on the juvenile period in geladas (Theropithecus gelada): the normative patterns of behavior and hormones during this understudied age group, the ontogeny of male-male bonds, and the overall effect of juvenile sociality and social development on dispersal and reproductive strategies. As expected, we documented an agerelated decrease in play but not grooming in both males and females, sex differences in the number of playmates and amount of time spent playing during the juvenile period, and a difference in grooming partner identity for males and females. We also found a U-shaped pattern in testosterone in juvenile males, analogous to that seen in juvenile male baboons. Our investigation into the formation of male-male bonds revealed a preference for same-age kin, although it is not clear that these bonds persist beyond the juvenile period as many males disperse alone. Importantly, we are finding a connection between dispersal strategy, dispersal timing and social integration, with more highly integrated males dispersing later and to bachelor groups and more isolated males dispersing earlier and to one-male units. Similarities between the gelada and human juvenile period make this project particularly relevant to humans. Like human children, and unlike most other primates, juvenile geladas interact socially with both relatives in their family unit and unrelated age-mates from outside their natal unit. Like human children, juvenile geladas return to their natal unit throughout the day and each night, and may behave differently with their peers and kin. Each natal unit has a unique combination of adults and juveniles, personalities and parenting styles. Thus, juveniles in the same peer group may experience very different social conditions. Our work examins the effects of these early social conditions on dispersal timing, dispersal strategy, and adult reproductive strategy, and will ultimately help provide a model for predictions about human development. Our work additionally provides a female-philopatric model for the development and function of male-male bonds, a valuable addition to a literature primarily focused on malephilopatric species. Publication plans We are currently writing up our results with the intent of publishing each chapter of the dissertation in a peer-reviewed journal in the coming year. Three papers (juvenile period patterns, utility of social networks, and patterns in juvenile gelada hormones) are in preparation, with at least three other papers being drafted. Detailed description of results First, we described sex differences and the normative trends in social behavior during the juvenile period for both male and female geladas. We also investigated play and grooming partner preferences for both males and females. We found that total social time does not vary with age or sex until age 5, at which point females socialize more than males (Figure 1). However, when the two components of gelada social behavior, play and grooming, are considered separately it become apparent that males and females differ in how they allocate their social time throughout the juvenile period. Play declines with age in both males and females, from a maximum at ages 0-1 to a minimum near zero by age 3 in females and age 6 in males (Figure 2). The decline is faster in females, and males play significantly more than females from ages 1-5. Grooming, in contrast, does not vary by sex until age 5, at which point females groom significantly more than males (Figure 3). The only age related difference in grooming rates is a significant increase in