Doctoral Dissertation Improvement: The ontogeny of male-male bonds in wild Ethiopian geladas (Theropithecus gelada)

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Although male-male bonds are relatively common in male-philopatric primates, evidence for these bonds in species with male dispersal is rare. Despite documentation that male-male bonds have reproductive consequences in this context, little is known about how these bonds develop. Doctoral student Caitlin Barale (Princeton University), under the supervision of Dr. Daniel Rubenstein, investigates the ontogeny of male-male relationships in the gelada (Theropithecus gelada), a species characterized by both male dispersal and male-male bonds. The primary objective of this research is to examine the nature of male-male bonds, and identify the behavioral and hormonal factors that set juvenile gelada males on individual reproductive trajectories as they transition from their natal one-male unit, to a temporary peer group, and onwards into an all-male bachelor group. The project has four specific goals: (1) to describe juvenile peer groups, (2) to characterize male-male bonds in the juvenile period, (3) to evaluate a short-term benefit of these bonds, and (4) to investigate how male relationships change at adrenarche. The investigators employ a combination of cross-sectional and longitudinal behavioral analyses, social network analysis and non-invasive fecal hormone sampling on all juvenile males (N=51) in a band of geladas in the Simien Mountains National Park, Ethiopia.This research represents the first long-term study focused exclusively on juvenile geladas. It provides a valuable new perspective on gelada social development through the collection of behavioral, physiological and network-based data, and initiates the first longitudinal dataset on known gelada males. Having detailed data on known individuals from juvenility to adulthood allows researchers to connect the effects of early life to lifetime reproductive success. The results of this research will contribute novel data on the development of male-male bonds in primates, advance the application of social network theory to animal systems, and help build a model for social development in early hominins, modern-day humans, and other non-human primates.