facial Width-height ratio (fWHR)

Sexual dimorphism in appearance is an important cue in social behaviour and may reflect intra-sex differences in mate-quality. In several primate species, facial-width-to-height ratio (fWHR) has been shown to be sexually dimorphic. Here we assess the fWHR in a large group (N=64) of brown Capuchin_monkey (Sapajus [Cebus] apella) of diverse ages, and examine whether fWHR is linked to dominance and status in either sex. fWHR showed significant sexual dimorphism, emerging during puberty. Furthermore, fWHR was positively associated with rated dominance and alpha-status, in both males and females. In the context of competition, immediately visible cues such as fWHR are particularly useful since they may obviate the need for physical fighting. This is the first report of an association between face-shape and dominance behaviour in non-human primates, and indicates that selection for facial width may be associated with intra-sex competition in both sexes.