Effect of Social Dominance and Reproductive State on Adrenal Steroids in Female Japanese Macaques (Macaca fuscata)

The relationship between stress and behavior can help us to understand how physiological adaptations shape primate societies. Most studies have focused on glucocorticoids (GC) as stress biomarkers, but other extrinsic and intrinsic factors can influence GC levels and confound the results. To overcome this issue, including analyses of dehydroepiandrosterone-sulfate (DHEAS), a GC antagonist, can be useful in evaluating overall adrenal function in response to biological, social, and environmental factors. Our goal was to evaluate the effect of reproductive state, social behavior, ambient temperature, and season (mating and non-mating) on DHEAS levels and the ratio between GC metabolites and DHEAS (GCM:DHEAS) in 11 free-ranging, female, Japanese macaques (Macaca fuscata) (7 pregnant/lactating, 4 nonpregnant/nonlactating) from Jigokudani Monkey Park (Japan). We validated and measured fecal DHEAS levels in 354 samples by enzyme immunoassay and calculated GCM:DHEAS by using previously reported data for GC metabolites. We tested the effects of reproductive state, dominance rank, social behavior, season, and ambient temperature on adrenal steroids using Generalized Linear Mixed-Effect Models. We found that pregnant and lactating females had higher DHEAS levels than nonpregnant/nonlactating females and that DHEAS levels were higher during the mating season. Temperature was positively correlated with GCM:DHEAS. Dominant females had higher DHEAS levels and lower GCM:DHEAS than subordinate females. We suggest that the high DHEAS to GC ratio in high-ranking females explains why they have better body condition than low-ranking females despite high GCM levels. This study confirms that including DHEAS provides valuable information for evaluating the stress response in primates.