Hunter, Jacob; Wood, Elizabeth; Jarman, Parker; Lindell, Stephen; Schwandt, Melanie; Goldman, David; Suomi, Stephen; Barr, Christina; Higley, James (Brigham Young University)
Faculty Advisor: Higley, James (Family Home and Social Sciences, Plant and Wildlife Sciences)
Rhesus monkeys (Macaca mulatta) are commonly used as a translational model to investigate human behavior and biology, largely due to shared evolutionary history and genetic similarities. Within rhesus monkeys, there are two distinct subgroups: Indian-derived and Chinese-derived monkeys. It is surprising that research has not compared the behavioral differences in these two subgroups. While there are anecdotal reports indicating that the Chinese-derived monkeys exhibit more aggression than the Indian-derived population, the only studies to investigate differences between them investigated infants, a limitation as infants rarely exhibit significant levels of aggression. This study investigates the relationship between DCA and several behavioral measures of aggression in adult subjects. We hypothesize that rhesus monkeys with higher DCA would exhibit more aggression than monkeys with lower DCA. The subjects were n = 130 adult female rhesus monkeys, housed in indoor-outdoor runs at the National Institutes of Health Animal Center, located in Poolesville, Maryland. Observations were made while the subjects were in their home cages, using five-minute focal observations, twice weekly for six months by trained staff. Subjects were behaviorally scored for a variety of behaviors that reflect rhesus monkey aggression. DCA was determined using genealogical data tracing each subject's ancestry back to the colony's founding in the 1940s. Based on the pedigree, the subjects were divided into pure Chinese-derived, pure Indian-derived, or hybrids. Repeated measures ANOVAs showed that 100% Chinese monkeys exhibited higher rates of aggression (F(2,125) = 14.02, p < .0001), when compared to the Indian-derived or hybrid monkeys. These results suggest that, consistent with anecdotal reports, monkeys with 100% DCA exhibit higher levels of aggression than Indian-derived or hybrid subjects. Aggression may have played a pivotal role in the evolutionary success of the Chinese rhesus, allowing them to cross the Himalayas, disperse throughout China, establish territory, and successfully compete with other species.