Social cohesion in yellow-bellied marmots is established through age and kin structuring

Individual characteristics and choices can influence social structure in animal groups. Social behaviour is likely to change throughout an individual’s life, resulting in different social roles at different ages. Individuals may also choose to interact differently with others based on their age, sex or kinship. We used social network analysis to examine biological correlates of individual social variation in free-living groups of yellow-bellied marmots, Marmota flaviventris. To measure social variation, we chose network measures that reflect an individual’s tendency to initiate or receive both direct and indirect interactions. We asked how age, sex and kinship influenced patterns of affiliative (socially cohesive) and agonistic (socially competitive) interactions. Specifically, we predicted that individuals would vary in their tendency to initiate and receive interactions according to these characteristics, and that they would be more likely to interact affiliatively with more similar individuals and to interact agonistically with more dissimilar individuals. We found that patterns of direct and indirect interactions changed significantly with age, with younger animals being more involved in affiliative interactions and older animals initiating more agonistic ones. Furthermore, affiliative networks tended to be structured by age and kinship. Our results suggest that yearling yellow-bellied marmots are more important for maintaining social cohesion than has previously been recognized, and that marmot colonies are largely organized based on age group and kinship.