Collaborative Research: Competition Within and Between Primate Social Groups: Hormonal and Behavioral Signatures

What are the costs and benefits of living in social groups of different sizes? Theory predicts that living in smaller groups should ease competition for resources within groups. But living in larger groups provides an advantage in competition between groups. These trade-offs between within-group competition (favoring smaller groups) and between-group competition (favoring larger groups) may mean that living in intermediate-sized groups is the best strategy for social species. However, this hypothesis has rarely been tested, and basic questions remain about how competition between individuals and groups affect an individual's energetic condition, and ultimately reproduction and survival. This study will address these questions by analyzing thyroid hormones - a modulator of metabolism and energy balance - in wild primates, in order to understand the relationship between group size, different types of competition, and energetic condition. The research will focus on a wild baboon population in Kenya studied for more than 45 years by the Amboseli Baboon Research Project. To pursue this innovative research direction, investigators will use a repository of approximately 8,000 already-acquired baboon fecal samples collected over a continuous 12-year period from over 200 adult females. Thyroid hormone metabolites will be compared to a rich dataset including information on individual group membership, group size, group movements, reproduction, and life span, among other information, to test the predictions surrounding the benefits of living in groups of varying size. In concert with the research goals, the investigators will build STEM talent and broaden participation of under-represented groups in behavioral ecology and biological anthropology by: (1) providing employment and training for a full-time research technician; (2) mentoring Stony Brook University graduate and Duke undergraduate students; and (3) developing and implementing a sustainable after school program in behavioral science that targets middle school students from high-needs districts. This research is co-funded by the Behavioral Systems Program in the Directorate for Biological Sciences and the Biological Anthropology Program in the Directorate for Social, Behavioral and Economic Sciences. How resource competition affects survival and reproduction in social mammals is a central topic in behavioral ecology and biological anthropology. This research will address this topic directly by empirically evaluating the tension between resource competition within and between social groups in a wild primate population. To do so, the investigators will quantify the concentration of thyroid hormones in approximately 8,000 already-acquired fecal samples from adult female baboons. The central premise is that variation in thyroid hormone concentrations provides a quantifiable index of individual energetic condition, which will vary as a function of competition for energy resources within and between groups. The resulting data will be analyzed in combination with detailed data on individual females and on social groups. Individual-level data will include social status, age, reproductive state, diet, and agonistic interactions; group-level data will include group size, group-level ranging patterns, intergroup encounters, and group stability. The research aims are to: (1) enhance our existing biological validation of fecal thyroid hormone analysis; (2) quantify the energetic consequences of social rank and group size; (3) assess the energetic predictors and consequences of changes in group size that occur through group fission events; and (4) understand the relative contributions of energetic versus psychosocial processes to variation in female endocrine profiles. This novel approach, which will provide an unprecedented window into the energetic consequences of social rank and group size, has rarely been applied to the study of wild primates and has never been applied to any project of this scale and scope. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.