Male juvenile golden snub-nosed monkeys acting as the mountee to receive grooming in their same-sex mounts

Abstract

Same-sex mounts provide male juvenile golden snub-nosed monkeys (Rhinopithecus roxellana) with opportunities to practice heterosexual copulatory skills and are often followed by grooming (post-mounting grooming, PMG). We hypothesized that juveniles acted as the mountee and provided mounting opportunities to receive grooming from their peer mounter. Here, we observed same-sex mounts among male juveniles (N = 5) in a captive group of R. roxellana in Shanghai Wild Animal Park, China from November 2014 to June 2015. Among 1,044 mounts recorded, 45.40% were accompanied by PMG initiated by the mounter, and only 3.74% were followed by PMG initiated by the mountee. Mountees were more likely to receive PMG when they performed a mounting solicitation than when they did not, or when they were mounted longer (even if they did not solicit). Over a long timeframe (one month), mountee’s tended to choose partners who groomed them more often than others after mounting, regardless of how long the grooming was. However, whether the mounter groomed the mountee did not predict the mounting direction in their subsequent mount. Our results suggest that in the context of same-sex mounts, juveniles provide mounting opportunities to receive grooming from peers on a long-term, rather than on a short-term basis. This study provides the first evidence that juveniles’ same-sex mounting strategy may be associated with the grooming market in non-human primates, which necessitates further investigation with large free-ranging groups due to the limited sample size of individuals and the captive setting of the current study.