Matrilineal Cohesion and Social Networks in Macaca fuscata

Abstract

In a provisioned troop of Japanese macaques (Macaca fuscata) in Arashiyama, Japan, greater adherence to Kawamura's rules of matrilineal rank inheritance and youngest ascendancy occurred among high-ranking females versus low-ranking females. Accordingly, high-ranking females formed more clustered hierarchies and low-ranking females had more dispersed hierarchies. A proximate explanation for this finding may be related to differences in how females maintain their social networks. To determine whether the clustering in the hierarchy was reflected in patterns of social cohesiveness, I compared network sizes of coalition and grooming partners for females in each third of the hierarchy. I calculated the proportion of available partners that were coalition and grooming partners within each category of relatedness (0.5 ≥ r ≤ 0.004 and r = 0). High-ranking females formed coalitions with a large proportion of their close relatives and a small proportion of their distant relatives; middle-ranking females supported an intermediate proportion of their close relatives and a small proportion of their distant relatives; and, low-ranking females formed coalitions with very few available close and distant relatives. High-ranking females groomed nearly all available close relatives and an intermediate proportion of distant relatives, whilst middle- and low-ranking females groomed a large proportion of available close relatives and a very small proportion of distant relatives. Thus, levels of clustering within the hierarchy appeared to reflect levels of social cohesion, in terms of grooming and coalition formation.