Disability and Dominance Rank in Adult Female and Male Japanese Macaques (Macaca fuscata)

Abstract

More than 30 years ago, Fedigan (Primate paradigms: sex roles and social bonds, 2nd, 1992 edn. Eden Press, Montreal, 1982) recognized and emphasized that social dominance was not just a reflection of physical size, strength and aggression in nonhuman primates but rather involved a multitude of complex factors and social dynamics. In the free-ranging group of Japanese macaques (Macaca fuscata) on Awaji Island, Japan, physical disabilities in the form of congenital limb malformations (CLMs) affect around 17% of the population. This group provides an opportunity to examine dominance rank in relation to physical impairment. Here, we present an analysis of dominance rank in the adult female and adult male Japanese macaques in the Awajishima group using behavioural data collected in 2005, 2006 and 2007 on 38 adult females (12 with CLMs) and in 2015 on 22 adult males (7 with CLMs). Once we controlled for matrilineal kinship, we found that disabled females tended to hold somewhat lower than expected dominance ranks. In contrast, disabled males were interspersed throughout the rank order, and disability was not associated significantly with dominance rank. However, age class had a statistically significant effect on dominance rank in males, such that older males tended to rank higher than younger males. Our results underscore Fedigan’s insights by demonstrating some of the complexities of dominance relationships in the context of the extensive physical variation shown in this group of Japanese macaques.