Colobus Monkeys in a Multilevel Society Show Frequent Adult Male Same-Sex Sexual Behavior with High Recurrence and...

The study of same-sex sexual behavior (SSB) has gained some attention in recent years, allowing us to reconsider our understandings of its evolution and adaptive value. Recent work has suggested expanding the definition of SSB to include courtship, pair-bonding, and other contextual information. Considering SSB within its behavioral context allows us to not only get at the function of SSB but also compare sequences of same-sex sexual behavior to different-sex sexual behavior. Using temporal-pattern analysis (TPA), we compared behavioral patterns of SSB and different-sex sexual behavior (DSB) in Rwenzori Angolan colobus monkeys (Colobus angolensis ruwenzorii). Over 6 months, we observed 82 sequences of sexual behavior, with 21% of these (N = 17) occurring between same-sex individuals. While rates of DSB were higher than SSB, their expression among age-sex classes trended similarly. Compared to closely related species, Rwenzori Angolan colobus engage in higher rates of SSB at older ages. TPA revealed that SSB and DSB patterns were similar, but patterns repeated more frequently for SSB than DSB. Our results suggest that SSB could be functional in Rwenzori colobus. We suggest that SSB among adult males in this subspecies may be adaptive if it promotes male social bonding within their multilevel society where more than half of the core units are multimale, multifemale.