Novel frameworks for explaining unequal access to the health benefits of social ties: a longitudinal analysis in wild chimpanzees

PROJECT SUMMARY Social integration and social support have profound and long-lasting effects on health and mortality. With such advantages, it is surprising that individuals vary so much in their ability to access the health benefits of social ties. In order to design more effective intervention and prevention strategies involving social support, it is vital to understand the factors that affect individual engagement with social networks, as well as which features of social relationships contribute most reliably to health outcomes. Research of this kind is quite difficult with human subjects given that long and complex social experiences are often distilled into broad subjective and retrospective measures of social support. Non-human primates have emerged as tractable and appropriate model systems for investigating interactions between social processes and health. Primate social bonds yield similar health or survival benefits to those in humans, yet social behaviors can be directly observed and objectively quantified. Chimpanzees are particularly valuable comparative models because they are long-lived and socially-complex, share a close genetic relationship with humans, and exhibit important similarities in social aging trajectories. The Kibale Chimpanzee Project has collected a dense, longitudinal sample comprising >25 years of systematic, daily observations of wild chimpanzee social behavior paired with routine monitoring for urinary biomarkers of stress and physiological health. The currently proposed work capitalizes on the extraordinary capacity of this dataset to elucidate long-term interactions between stress response systems, social relationship maintenance, and aging. The overarching goal of this research is to elucidate the factors that affect unequal access to the health benefits of social ties. Our innovative approach centers on the perspective that the development of beneficial social support networks entails costly investments and the risk of stressful, health-compromising experiences. We hypothesize that both early development and aging shape individual sensitivity to relationship stress, which affects how individuals engage in their social environments. Aim 1 will evaluate how body size and trait glucocorticoid function, factors influenced by development, predict investment in and quality of social relationships. Aim 2 will evaluate how relationship quality attributes, such as the stability and equitability of bonds and the balance of positive and negative interactions, moderate the influence of social bonds on health and mortality. For Aim 3, we will integrate the results of Aims 1 and 2 into a comprehensive framework by addressing whether individual developmental traits interact with social relationship quality or act independently to shape health, and how these influences are modified by changes in sociality during aging. The planning phase of the research will involve necessary data preparation and development and validation of novel analytical tools for assessing trait glucocorticoid variation and the multidimensional properties of social bonds.