title: Sexually selected lip colour indicates male group-holding status in the mating season in a multi-level primate society.
abstract: Sexual selection typically produces ornaments in response to mate choice, and armaments in response to male-male competition. Unusually among mammals, many primates exhibit colour signals that may be related to one or both processes. Here, we document for the first time correlates of facial coloration in one of the more brightly coloured primates, the black-and-white snub-nosed monkey (Rhinopithecus bieti). Snub-nosed monkeys have a one-male unit (OMU) based social organization, but these units aggregate semi-permanently into larger bands. This form of mating system causes many males to become associated with bachelor groups. We quantified redness of the prominent lower lip in 15 males (eight bachelors, seven OMU holders) in a group at Xiangguqing, China. Using mixed models, our results show that lip redness increases with age. More interestingly, there is a significant effect of the interaction of group-holding status and mating season on redness; that is, lip colour of OMU males undergoes reddening in the mating season, whereas the lips of subadult and juvenile bachelor males become paler at that time of year. These results indicate that lip coloration is a badge of (group-holding) status during the mating season, with non-adults undergoing facial differentiation, perhaps to avoid the costs of reproductive competition. Future research should investigate whether lip coloration is a product of male-male competition, and/or female mate choice.
authors.affiliation: School of Anatomy, Physiology and Human Biology, The University of Western Australia Crawley/Perth, Western Australia 6009, Australia.
authors.forename: Cyril C
authors.initials: CC
authors.lastname: Grueter
authors.affiliation: Key Laboratory of Animal Ecology and Conservation Biology Institute of Zoology, Chinese Academy of Sciences Beijing 100101, People's Republic of China.
authors.forename: Pingfen
authors.initials: P
authors.lastname: Zhu
authors.affiliation: School of Biological, Biomedical and Environmental Sciences, University of Hull Hull HU6 7RX, UK.
authors.forename: William L
authors.initials: WL
authors.lastname: Allen
authors.affiliation: Center for the Study of Human Origins, Department of Anthropology New York University New York, NY 10003, USA.
authors.forename: James P
authors.initials: JP
authors.lastname: Higham
authors.affiliation: Key Laboratory of Animal Ecology and Conservation Biology Institute of Zoology, Chinese Academy of Sciences Beijing 100101, People's Republic of China.
authors.forename: Baoping
authors.initials: B
authors.lastname: Ren
authors.affiliation: Key Laboratory of Animal Ecology and Conservation Biology Institute of Zoology, Chinese Academy of Sciences Beijing 100101, People's Republic of China.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
keywords: Rhinopithecus; coloration; multilevel society; primate; reproductive seasonality; sexual selection