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

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.

在群居物种中，个体往往拥有偏好的亲和性社交伙伴，与其建立的社交纽带或联结所能带来的益处，往往与更高的适合度（fitness）相对应。例如，在成年雌性狒狒与幼年马中，拥有更牢固或更频繁社交联结的个体存活率更高。我们借助详尽的行为与生活史记录，探究了群居性猴类——斯氏青猴（Cercopithecus mitis stuhlmanni）——的社交纽带质量与存活率之间的关联，同时控制了优势等级、群体规模与生活史策略这几项变量。我们采用Cox比例风险回归模型（Cox proportional hazards regressions），针对83只已知年龄的野生成年雌性个体，对其在8个社交群体中的2至8年（总计437个观察年）的生存数据进行建模，分别刻画了社交纽带与死亡风险之间的累积（多年度）与即时（单年度）关联。在特定条件下，与亲密伙伴建立的联结强度与更高的死亡风险呈正相关：相较于采取其他社交策略的雌性，那些与亲密伙伴的联结在多年间缺乏一致性的雌性，其死亡风险显著更高。在单年度范围内，若雌性个体的亲密伙伴相较于上一年发生了更替且二者存在牢固联结，则其死亡风险会高于伙伴关系保持稳定的雌性。优势等级、群体内成年雌性同伴数量以及首次繁殖年龄均无法预测死亡风险。本研究表明，牢固社交纽带的收益与代价并非固定不变，而是取决于社交伙伴关系随时间推移的一致性程度。