Oxytocin and Aggression in Verreaux's Sifaka (Propithecus verreauxi) in Kirindy Mitea National Park, Madagascar

Abstract

Many species, particularly group-living species, display aggression. To help understand the biological basis of aggression, aggression is often analyzed with hormonal biomarker levels, but this usually occurs in highly aggressive species. Therefore, we know little of the patterns of aggression and its hormonal mechanisms in low-aggression species. Aggressive behaviors in such species may serve different functions or occur through different mechanisms. The goal of this study is to examine intragroup aggression in male and female P. verreauxi, a low-aggression species with female power over males. Aggression may be inhibited by higher levels of oxytocin (OT), so I examine the relationship between aggression and OT in males and hypothesize that they are negatively associated. I explore aggression patterns in male and female P. verreauxi using data from January 2007 to December 2019. We use enzyme-linked immunosorbent assays (ELISAs) to determine OT levels in male urine samples from July 2018 and January through March 2019. I found that females had higher rates of aggression than males, that most aggression occurred during the mating season, and that males received the most aggression from females while females received the most aggression from males during the mating season. Also, male OT levels were lower during the mating season compared to the non-mating season. Contrary to expectations, aggression rate was not a significant predictor of male OT levels, though they showed inverse seasonal patterns. The results of this study support previous research indicating that aggression is one means of achieving female power over males and suggest that male OT levels are not directly related to intragroup aggression. However, future research should explore whether OT levels are associated with intergroup rather than intragroup aggression.