1National Institute of Nursing Research, National Institutes of Health, 2Department of Anthropology, The George Washington University, 3Department of Anthropology, Northern Illinois University, 4Department of Anthropology, University of Illinois at Urbana-Champaign
Thursday All day, Clinch Concourse
Tamarins live in small multimale-multifemale social groups in which subordinate adult females are reproductively suppressed. In order to better understand the physiological consequences of female and male reproductive competition, we measured cortisol in hair samples (time-averaged index of hypothalamic-pituitary-adrenal axis activation) collected from 7 groups of wild saddle back tamarins (N=22 males and N= 16 females) trapped, marked, and released during June 2012, in northern Bolivia (11º 23’ S, 69º 06” W’). This research is part of an ongoing study examining tamarin reproductive ecology. We explored whether group size, number of adult males/females in a group, and female reproductive category (nulliparous or multiparous) contributed to variation in hair cortisol.
We validated and used commercially available kits designed for salivary cortisol analysis, and employed dilutions suggested by previous analysis of captive marmoset hair cortisol. Our results suggest that while the number of adult males in a group or reproductive category are not significant predictors of hair cortisol, the number of adult females in a group is – specifically, groups with three adult females had significantly higher hair cortisol than groups with two adult females (t-test, t=-2.521, df=9.541, p=0.031). This effect is tied to group size, where females in larger groups (7+) have significantly higher hair cortisol than individuals in smaller groups (≤5) (t-test, t=-2.466, df=14, p=0.027). Although the effects of these differences on reproductive outcome or social grouping remain unclear, it is possible that larger group size creates more stress for subordinate females, and may contribute to their emigration.
Supported in part through research funds provided by the University of Illinois, Urbana-Champaign and the Center for Latino and Latin American Studies at Northern Illinois University.