Examining postmounting grooming in male golden snub-nosed monkeys to investigate the functions of same-sex mounts.

Same-sex mounting behavior has been documented across primate species and several biological functions, that are often difficult to differentiate, have been proposed. Postmounting affiliative behaviors (e.g., embracing and grooming) have been partly overlooked and their performance may more clearly reveal the function of same-sex mounts for different age-sex classes. Here, considering postmounting grooming behaviors (PMG), we tested the affiliation hypothesis for same-sex mounts in an all-male unit (AMU) of captive golden snub-nosed monkeys (Rhinopithecus roxellana) (n = 7-8) and the needing to learn hypothesis in the juveniles of the AMU (n = 4) and the juvenile male from the neighboring one-male unit in Shanghai Wild Animal Park, China from November 2014 to June 2015. A total of 1986 same-sex mounts were recorded from the AMU individuals and the juvenile of the neighboring one-male unit. We found that neither dyadic proximity-based association nor grooming-based affiliation predicted the occurrence of mounts in the AMU, and PMG was more likely to occur in nontense than tense social contexts, providing no support for the affiliation hypothesis. Although dyadic grooming-based affiliation predicted the occurrence of PMG, it exerted no influence on the occurrence of mounts, which was necessary to support the hypothesis. However, consistent with the needing to learn hypothesis, from ages two to four, juveniles' mounting duration increased and they performed pelvic thrusting during mounting more and more often as they grew older. Reciprocated series mounts were much more common among juveniles than other mounting dyads, providing learning opportunities for both participants. The mounter was more likely to groom the mountee at the end of a mount among juveniles than other mounting dyads, suggesting that juvenile mounters may profit from mounting and groom mountees in return for providing them with opportunities to learn copulatory skills. A hypothesis that merits further investigation.

Human activities and elevational constraints restrict ranging patterns of snub-nosed monkeys in a mountainous refuge.

Both natural conditions and anthropogenic factors affect the survivability, distribution, and population density of wildlife. To understand the extent and how these factors drive species distributions, a detailed description of animal movement patterns in natural habitats is needed. In this study, we used satellite telemetry to monitor elevational ranges favored by endangered golden snub-nosed monkeys (Rhinopithecus roxellana), in the Qinling Mountains, central China. We investigated the abundance and distribution of food resources through sampling vegetation quadrats at different elevations and sampled anthropogenic activities using field surveys. Our results indicated that although there was no significant variation in food resources between low- (<1500 m) and middle-elevations (1500-2200 m), monkeys were found most often in areas above 1500 m, where there was less anthropogenic development (e.g. houses and roads); however, monkeys rarely ranged above 2200 m and had limited food availability at this altitude. There was limited human disturbance at this elevation. We suggest that both human activity and ecological constraints (i.e. food resources) have considerable effects on elevational use of R. roxellana in the Qinling Mountains. This study highlights the critical roles these factors can play in shaping the vertical distribution of high-altitude primates. This research provides useful insights for habitat-based conservation plans in which human disturbance management and habitat restoration should be prioritized.

The influence of a demographic change on social relationships among male golden snub-nosed monkeys (Rhinopithecus roxellana).

It has been suggested that social relationships are more likely to be prone to variation in the dispersing sex than the philopatric sex. However, we know less about the dynamics of all-male groups in male-dispersing species than we do about other types of primate groups. We studied male sociality in a captive group of golden snub-nosed monkeys (Rhinopithecus roxellana), which was composed of a one-male unit (OMU, N = 7) and an all-male unit (AMU, N = 7 or 8), in Shanghai Wild Animal Park, China. Using data collected for 6 months, during which there was a demographic change in the AMU and the alpha male was replaced by a newcomer, we found that a dramatic change in social ranks occurred accompanied by elevated aggression following this social upheaval. A proximity-based social network analysis revealed that members did not associate randomly any more but formed differentiated relationships post-upheaval, resulting in three distinct sub-units in the AMU. In terms of inter-unit interactions, significant changes were found in the affiliations between the male juvenile of OMU and AMU individuals. He interacted with AMU individuals randomly and frequently pre-upheaval, but cut down his affiliations and had a preferred partner post-upheaval, who was a member of the dominant male's sub-unit. Our findings suggest that social networks in the dispersing sex are dynamic structures and vary by some demographic change (e.g., individual immigration) in the studied species. We also put forward that individual dominance could be a criterion when the male juvenile chooses partners before he immigrates into a group. In conclusion, the high level of behavioral flexibility of the dispersing sex could be an evolutional strategy and good for individuals' future dispersing life.

Do same-sex mounts function as dominance assertion in male golden snub-nosed monkeys (Rhinopithecus roxellana)?

It has been hypothesized that same-sex mounts can reflect the hierarchical relationship in a mounting dyad and it is widely deemed that mounting and being mounted are demonstrations of dominant and subordinate status, respectively. In this research, we aimed to test whether same-sex mounts function as dominance assertion in male golden snub-nosed monkeys (Rhinopithecus roxellana). We investigated this behavior in eight-individuals, captive all-male unit (AMU) in Shanghai wild animal park, China. Behavioral observations were conducted with a total of 1,855 mounts recorded from November, 2014 to June, 2015, during which the alpha male was replaced in the beginning of April. In support to the dominance assertion hypothesis, we found that during the entire study period the higher-ranking male was more likely to be the mounter than the lower-ranking one, except the mounts that happened among juveniles in peaceful and playful social contexts. Our study indicates that the hierarchical relationship of a mounting dyad can be influenced by the age-class of the participants and the social context where mounting occurs. We suggest that same-sex mounts might have different functions in different age groups and be multifunctional in a species.