Stronger social bonds do not always predict greater longevity in a gregarious primate.

Nicole A Thompson,Marina Cords

doi:10.1002/ece3.3781

Abstract

In group‐living species, individuals often have preferred affiliative social partners, with whom ties or bonds can confer advantages that correspond with greater fitness. For example, in adult female baboons and juvenile horses, individuals with stronger or more social ties experience greater survival. We used detailed behavioral and life history records to explore the relationship between tie quality and survival in a gregarious monkey (Cercopithecus mitis stuhlmanni), while controlling for dominance rank, group size, and life history strategy. We used Cox proportional hazards regressions to model the cumulative (multi‐year) and current (single‐year) relationships of social ties and the hazard of mortality in 83 wild adult females of known age, observed 2–8 years each (437 subject‐years) in eight social groups. The strength of bonds with close partners was associated with increased mortality risk under certain conditions: Females that had strong bonds with close partners that were inconsistent over multiple years had a higher risk of mortality than females adopting any other social strategy. Within a given year, females had a higher risk of death if they were strongly bonded with partners that changed from the previous year versus with partners that remained consistent. Dominance rank, number of adult female groupmates, and age at first reproduction did not predict the risk of death. This study demonstrates that costs and benefits of strong social bonds can be context‐dependent, relating to the consistency of social partners over time.

Highlights

Among social animals, individuals commonly have differentiated relationships, or ties, with others
We found that stronger bonds do not necessarily increase survival in females in a matrilocal, gregarious species
In adult female blue monkeys, stronger bonds with close social partners decreased survival when close partners were inconsistent over time

Summary

| INTRODUCTION

Individuals commonly have differentiated relationships, or ties, with others. Blue monkeys differ from other cercopithecines in multiple ways, we expected to confirm patterns documented in certain macaques (Lehmann et al, 2016) and baboons (Archie et al, 2014; Silk et al, 2010b), namely, that more or higher-quality social ties, either cumulatively over multiple years or in one’s current environment, correspond with higher survival Unlike these other species, blue monkeys are highly arboreal, live in a less seasonal (rainforest) environment, seem to experience relatively strong feeding competition between groups but relatively weak competition within groups (Cords, 2007; Klass & Cords, 2015), and live in groups with a single male. We predicted that females that maintained consistent and strong bonds with their closest partners would have a survival advantage relative to females with weak and inconsistent bonds, and that the benefits of strong and consistent bonds would be more pronounced over the long term

| MATERIALS AND METHODS

| DISCUSSION

Findings

| CONCLUSIONS