Male–Male Affiliation in Sulawesi Tonkean Macaques

Abstract

Research during the early years of field primatology was primarily centered on the more conspicuous individuals (i.e., males) and behaviors (i.e., aggression), and in particular, males engaged in aggression (Bygott 1974; Hausfater 1975; Popp and DeVore 1979). Since that time, subsequent field research has increasingly revealed the importance of affiliation within primate social groups (Strum 1982, 2001; Smuts 1985; Strier 1994; Gould 1994; Silk 2002), leading some to argue for a renewed attention to the potential role it played in the evolution of primate sociality (Sussman et al. 2005). The primary focus of most of this work has been on the importance of affiliative and cooperative relationships between females and between males and females. Male-male relationships, however, remained largely viewed through the lenses of aggression and dominance (Hill and van Hooff 1994). This is because primate socioecological theory predicts that males and females compete for different resources (i.e., access to mates and food, respectively), and affiliative and cooperative behavior is expected to be high among females and low among males (Trivers 1972; Wrangham 1980). There is, however, increasing evidence that the nature of male-male relationships may be more diverse than previously thought (van Hooff and van Schaik 1994). For example, in 1994, an entire volume of the journal Behaviour was devoted to the topic of male-male bonding. Six years later, an edited volume titled Primate Males (Kappeler 2000) provided further evidence of the complexity of primate males, particularly with regard to male-male interactions and the role males play in shaping social organization. A number of these papers explore the key variables, both proximate and ultimate, that explain the occurrence of affiliation among males. Male philopatry and kinship have been identified as two of the most important variables (van Hooff and van Schaik 1994). The common chimpanzee represents a good example of male bonding in a male philopatric species; male chimps have been observed to form strong male-male alliances and engage in high levels of mutual grooming (Nishida and Hiraiwa-Hasegawa 1987). At the same time, although less common, male bonding has been observed in species in which males disperse, thereby suggesting that kinship need not be a prerequisite for male-male affiliation (Silk 1994; Hill and van Hooff 1994).