Effects of progressing age on energy balance, sociality and health in wild female Assamese macaques (Macaca assamensis)

Prof. Dr. Julia Ostner, Göttingen

PhD student: Sofia Vilela

As humans age they decrease their social activity and become increasingly selective in their partner choice favoring valuable relationships over less meaningful ones. This socio-emotional selectivity has been attributed to the limited time perspective of the elderly. Likewise in nonhuman primates, social activity and number of social partners decline with increasing age, but in the absence of awareness of limited time. I propose that the declining social activity with progressing age is partly driven by energetic constraints due to age-related decreases in foraging performance, energy intake and energy balance. The combination of a poor energy balance with decreasing sociality pose energetic as well as social stressors, which both are expected to increase physiological stress levels, which in turn diminish an individual´s health. In this project on our long-term study population of wild Assamese macaques (Macaca assamensis), we combine data on age-related changes on foraging efficiency, nutritional intake and energy balance, measures of social integration, physiological measures of nutritional and social stressors with indicators of health, specifically the gut microbial community and a non-specific immune marker. This project has three main goals: First, we will add to the few studies on behavioral gerontology in populations under natural ecological conditions enabling us to integrate energetic constraints as an important but rarely investigated factor limiting social activity. Second, we aim to separate in aged individuals physiological responses to energetic stressors from responses to social stressors by simultaneously measuring a non-specific marker of the stress response (urinary glucocorticoid levels) and a nutritional hormone marker (thyroid hormone levels). Lastly, we link age-related energetic constraints, physiological stress responses and measures of social integration to health indicators. Together, these data will contribute to a comprehensive understanding of the role of energetic factors on social activity and selectivity with increasing age and will inform studies on human behavioral gerontology.

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