Male Cooperation in Primates: Physiological Correlates of Intra- and Intergroup Relations

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Social bonds and prosocial behaviors are fundamental aspects of many primate groups, including humans, yet the evolutionary roots and physiological underpinnings of these behaviors are poorly understood. This project will use hormonal, energetic, and behavioral data for two non-human primate species to better understand prosocial behaviors and male cooperation in primates. The study is unique in that it specifically will examine the potential physiological mechanisms that are associated with positive male-male social interactions within groups and with collective male aggression between groups. The findings will contribute to a broader understanding of the role of cooperation in primate evolution. This project will expand the PI's long-term commitment to international collaborations and educating STEM students and researchers. The field component involves training assistants in methods for behavior, ecology, and conservation research, while the laboratory component of this study will provide opportunities for University of Texas undergraduate and graduate students to receive training in modern molecular techniques. Through public outreach and conservation education by the PI and senior research personnel in both the US and abroad, the project will also support global primate and habitat conservation efforts.This project requests funds for a two-year study to characterize the physiological correlates of male social relationships among spider monkeys (Ateles belzebuth) and woolly monkeys (Lagothrix poeppiggi) in Yasuní National Park, Ecuador. The investigators will combine hormonal analyses with field observations, to 1) characterize interspecific and interindividual variation in testosterone (T) and glucocorticoids (GCs), and behavioral responses to both intra- and intergroup aggression, and 2) examine how this variation is influenced by the strength of intragroup social bonds and the intensity of between-group competition. Both spider and woolly monkeys are characterized by high rates of male-male affiliation and low rates of male-male aggression within groups. However, patterns of aggression between groups differ between these two species: boundary patrols and aggressive encounters between males from different groups of spider monkeys are among the most dramatic examples of collective aggression seen in non-human primates, paralleled only by the intergroup "warfare" seen in some populations of chimpanzees, while encounters between woolly monkey groups are frequently more tolerant. Thus this study will begin to untangle how the behavioral expression of similar physiological responses may be affected differently by individual versus group-level competition.