Influence of maternal kinship on association network structure in a long-term study of spider monkeys (Ateles geoffroyi)

Maternal kinship can structure social relationships in mammals, as demonstrated in species characterized by female philopatry. In these species, females tend to be closely related and interact more often with maternal relatives. However, there is limited evidence indicating a role of maternal kinship in species characterized by male philopatry. To increase our understanding of the role of maternal kinship on the social structure of these species, we explore how maternal kinship influences the structure of association networks in a group of wild Geoffroy's spider monkeys, Ateles geoffroyi, over 24 years. Using 53 546 instantaneous scan samples collected from 1997 to 2020 (mean ± SD = 2231 ± 890 per year), we built yearly association networks using the simple ratio index to establish links among 93 individuals observed over the study period. We used generalized linear mixed models (GLMMs) and vector generalized linear models (VGLMs) to examine whether edge weight, network modularity and eigenvector and betweenness centrality were related to five maternal kin categories, four age-difference classes, three sex classes and matriline membership. We found that among individuals of similar age difference, maternal kin had higher edge weight and higher probabilities of being assigned to the same module in the association network than nonmaternally related individuals; maternal brothers, maternal sisters and maternal female–male siblings associated more than nonmaternally related individuals; and matriline membership influenced the eigenvector and betweenness centrality of its members, resulting in higher centrality values within certain matrilines. Matriline size was positively associated with eigenvector centrality, indicating that members of larger matrilines tended to be better integrated into the overall network through close connections with their maternal kin. Our results suggest that, in addition to age and sex, maternal kinship plays a significant role in structuring association networks even in a species characterized by male philopatry.