IMG_7570In many primate societies, individuals form strong, long-lasting social bonds. It is now known that these bonds can be adaptive, for example by increasing longevity, offspring survival, and, ultimately, reproductive success. What is still poorly understood are the mechanisms by which social bonds achieve their effects. One possibility is that because of their known function in helping individuals cope with stressors, social bonds mitigate negative effects of chronic stress on health and reproduction. But whether – and how – social stress in wild social groups of primates influences female reproduction is also poorly understood.

The Tokai Baboon Sociality Project addresses these gaps in our knowledge by testing three potential pathways that could connect variation in social bonds with measures of health and reproductive function: 1) the lack of strong social bonds leads to elevated stress hormone levels that in turn mediate increased susceptibility to intestinal parasite infections, with potential effects on energy availability; 2) social stress influences reproductive physiology directly; 3) social bonds mediate success in feeding competition; and 4) social bonds (particularly with males) reduce exposure to aggression and infanticide risk.

Foerster-2014-001-IMG_7627Data for this project are currently being collected from two troops of chacma baboons (Papio ursinus) on the Cape Peninsula of South Africa. Methods include (1) behavioral observations to document sources of stress and social bonds; (2) measurement of stress and reproductive hormone levels in fecal samples; (3) examination of intestinal parasites from fecal samples; (4) measurement of energy balance via urinary C-peptide, a byproduct of insulin production; and (5) a novel field experiment in which intestinal parasites are eliminated from a random selection of females to assess, for the first time in a wild primate, the factors associated with the timing and intensity of re-infection.

Ultimately, this project will generate new insights into the mechanisms linking social behavior, stress physiology, health, and reproduction and help elucidate the function of social bonds in primate societies. Because baboons share many traits with humans and are useful in studying aspects of human biology, this project will both help us understand the benefits of sociality during human evolution and carry clinical implications by elucidating the role of social stress as a risk factor for parasite infections.