The Effects of Early Social Context and Social Types on Dispersal and Reproductive Strategies in Male Geladas (Theropithecus gelada)

Abstract

The relationship between early social experiences, dispersal, and adult strategies is complex. It requires a thorough investigation into the social environment of immature study subjects, and the ability to track individuals as they mature, disperse and reproduce. In this dissertation, we use behavioral observations and social network analysis to explore the development of individual differences in social integration during the juvenile period, the facets of early life that influence these differences, and the way they influence behavioral trajectories in male geladas (Theropithecus gelada). Sex differences foreshadowing adult trajectories were apparent in play rates, number of playmates per individual, grooming partner type, and partner preferences. Males practiced fighting and assessing competitors, while females built grooming ties with relatives. Both sexes exhibited individual consistency in play and grooming rates. In addition to individual differences in interaction rates, individuals varied in social integration, as measured by social network analysis. Within a specific social context, geladas who had many friends also connected disparate subgroups and had well-connected partners. However, social prowess in one setting did not translate into competence in another. The combination of interaction rates and integration metrics was individually stable over time for the majority of individuals and constituted repeatable "social types". Social types arose primarily from variation in maternal sociability. Sons of highly-social mothers (who provided sons with a grooming network template) were well-integrated in juvenile grooming networks, while sons of less-social mothers actively built their own play networks. Social types also influenced dispersal trajectories. Males who were highly or moderately integrated in juvenile social networks positioned themselves to be highly successful adults. They stayed in their natal units long enough to learn and practice the social skills necessary to integrate into a bachelor group, and dispersed into bachelor groups either directly (highly integrated males) or by visiting first to improve their grooming skills (moderately integrated males). Poorly-integrated males did not attempt to join bachelor groups and instead dispersed at young ages directly into reproductive units. Additional research is needed to firmly connect differences in integration and dispersal patterns to reproductive strategies, although these initial results support a connection between early social integration and adult strategies.