The transition to motherhood as the temporal locus of change for social network integration among wild vervet monkeys

Abstract

The birth of a first offspring represents a major change in a female mammal’s social circumstances. We hypothesize that the transition to motherhood marks a significant shift in the social network dynamics of female vervet monkeys, Chlorocebus pygerythrus, and represents the crucial boundary between juvenile and adult patterns of engagement. To test this, we compare the grooming network structure of primiparous and multiparous females, using both direct and indirect measures of centrality. We found that, following the birth of their first infant, ego-structure of primiparous females converged with that of multiparous females and that primiparous females became more central in their grooming networks around their first birth event, as measured by eigenvector centrality. Examining shifts in the number of new social ties formed across the birth event, we found a very small increase in the formation of new strong ties, but a larger increase in the number of additional weak ties. A simulated ‘knockout’ analysis showed that both types of ties contributed to the observed increase in eigenvector centrality. Overall, our findings support the idea that motherhood serves as a catalyst for juveniles to transition into adult social configurations. Note, however, that although the juvenile–adult boundary marked the temporal locus of change for social integration, there was, nevertheless, a striking consistency in the stability of ego-network structure across both the juvenile period and through the motherhood transition. This structure may enhance individual flexibility in social engagement and accommodate the specific needs of females as they experience changes in status and broader demographic shifts within their groups.