Golden Snub-Nosed Monkeys
Blog 3 by Olivia Isetts-Williams
Figure 1: An OMU Family Unit of Golden Snub-Nosed Monkeys (Shanghai Wild National Park, 2024)
Social Organization
Golden Snub-Nosed monkeys are composed of one-male, multi-female units (OMUs) and all-male units (AMUs) (Kirkpatrick & Grueter, 2010), and their group sizes fluctuate seasonally (Figure 2). These seasonal, or fission-fusion societies may contain up to 600 individuals in the summer, while winter groups break into smaller subgroups of 60-70 individuals, and is reformed as food scarcity rescinds amidst fruiting seasons in the spring (Munoz, 1999). Subgroups are divided into numerous OMU and AMU family units, composed of males, females, and their offspring (Figure 1). AMU’s form following the separation of young males from family units, creating harems influenced by age hierarchy, and formulate the basis of understanding kinship patterns throughout Snub-Nosed monkey units. Females within units retain their family groups, typically for life, while male offspring are forced to leave by their fathers as early as three years of age (Gron, 2007).
Figure 2: Diagram of mating patterns observed in primates, including Promiscuity, Polygamy, and Monogamy (Binz, 2016)
Social Structure
The relationships that are built within OMUs are kin-based (Cerrone, 2024), but remain peaceful across between-group relations with those of the same species. These interactions and relations amongst associated OMUs coalesce into cohesive breeding bands, in which different groups have been observed to venture, forage, and rest together within overlapping home ranges (Cerrone, 2024). Aggression amongst AMUs possess an observable positive correlation during mating months with OMUs, though typically appear neutral and unobtrusive amidst non-mating seasons (Zhang, et al. 2010).
Mating System
Golden Snub-Nosed monkeys form polygamous groups defined as polygyny and harem style structures (Figure 2), which specifies their one-male multi-female and all-male units. The direct and high-intensity male competition incited by these structures is directly observable by sexually dimorphic extremes. Snub-Nosed monkeys are the largest of the Colobines, and the juxtaposition of body sizes between sexes amplifies this factor; females range from an average of 8 or 9 kilograms, while their male counterparts weigh in at a striking 15 kilograms (Kirkpatrick & Grueter, 2010). Canine sizes of male Golden Snub-Nosed monkeys are also significantly larger, a signifier of direct male competition, and their larger testes lend to implications of indirect sperm competition between other males (Kirkpatrick & Grueter, 2010). While swelling and coloration in Golden Snub-Nosed monkeys is not as apparent as other Snub-Nosed species, males have been observed to develop red wart-like growths on the corners of their mouths, which are theorized to represent the sexual maturity that occurs at age seven (Liang, 2000).
The OMU structures observed along bands are constantly changing, as females freely leave their resident male to join new OMUs and males enact takeovers of other OMUs (Yang, 2021). Stability and alterations of these groups, as well as mating, are most typically initiated by female choice, creating dynamics ultimately influenced by intersexual selection.
While reproductive skew has not been strongly observed in Golden Snub-Nosed monkeys, the degree of sexual dimorphism observable amongst males and the trend of females leaving one OMU for another indicates a notable likelihood in female preference for one male presentation over another; females dictate the success of a male, and males who reside within a harem possess a disproportionate lack of success compared to resident males.
Care System
As a result of their social structures with limited males and an abundance of females, one male is likely to breed with several females amidst the three-month mating period. This generates paternity confidence, which increases likelihood of males assisting the female amidst infant care. This can be seen through protection and grooming on behalf of the males, while the females typically provide most of the care until the infants wean off of their mothers (Munoz, 1999). Paternal behaviours are less prevalent when infants are male. This is due to the social pressure for males to depart from their familial care systems to join new groups, a strategy that avoids inbreeding and overlap of resident males within the same OMU (Gron, 2007).
References
Binz, K. (2019, February 16). An introduction to primate societies. Fewer Lacunae. https://kevinbinz.com/2016/07/17/an-introduction-to-primate-societies/
Cerrone, M. (2024, August). Golden snub-nosed monkey, Rhinopithecus Roxellana - new england primate conservancy. New England Primate Conservancy. https://neprimateconservancy.org/golden-snub-nosed-monkey/
Gron, K. (2007, November 20). Golden snub-nosed monkey. Wisconsin National Primate Research Center. https://primate.wisc.edu/primate-info-net/pin-factsheets/pin-factsheet-golden-snub-nosed-monkey/
Kirkpatrick, R. C., & Grueter, C. C. (2010). Snub‐nosed monkeys: Multilevel societies across varied environments. Evolutionary Anthropology: Issues, News, and Reviews, 19(3), 98–113. https://doi.org/10.1002/evan.20259
Munoz, P. (1999). Rhinopithecus Roxellana (Golden Snub-nosed monkey). Animal Diversity Web. https://animaldiversity.org/accounts/Rhinopithecus_roxellana/
Yang, X., Berman, C. M., Hu, H., Hou, R., Huang, K., Wang, X., Zhao, H., Wang, C., Li, B., & Zhang, P. (2021). Female preferences for male golden snub-nosed monkeys vary with male age and social context. Current Zoology, 68(2), 133–142. https://doi.org/10.1093/cz/zoab044
Zhang, J., Zhao, D., & Li, B. (2010). Postconflict behavior among female Sichuan snub-nosed monkeys Rhinopithecus roxellana within one-male units in the Qinling Mountains, China. Current Zoology, 56(2), 222–226. https://doi.org/10.1093/czoolo/56.2.222
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