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

• Published in: Ecology and evolution Vol. 8; no. 3; pp. 1604 - 1614
• Main Authors: Thompson, Nicole A., Cords, Marina
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-02-2018; John Wiley and Sons Inc
• Subjects: Animal behavior; Baboons; Bonding strength; Cost benefit analysis; Dominance; Females; Fitness; Group size; Hazards; Horses; Life history; Mortality; Original Research; Risk; Social bonds; social partner consistency; social relationships; social ties; Survival; Kenya; social partner consistency; social ties; social relationships; fitness; survival
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.3781

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.
We categorized adult female blue monkeys according to the strength and consistency over time of their closest social ties. Females that had strong but inconsistent ties had a higher risk of death than females in all other categories. Social dominance rank, group size, and life history strategies did not influence mortality.