Abstract
A large body of evidence suggests that female Old World monkeys maintain selective long-term grooming interactions with fitness benefits. The last two decades have produced evidence that the regulation of social interactions among primates can be, in part, explained by the Biological Markets theory, with grooming behaviour as the focus of these studies. Grooming facilitates bonding between individuals, constituting an essential part of the regulation of social relationships among female cercopithecids. In contrast to the well-studied baboons (Papio spp), knowledge about the nature of grooming interactions and their regulation is generally lacking for the large, terrestrial species of mandrills (Mandrillus sphinx). We used a combination of social network analysis tools and well-established methods for assessing partner diversity and reciprocity to characterise grooming networks, partner choice and patterns of trade (be groomed, give grooming) among females in a captive group of mandrills, both within and across two separate observation periods. Our results suggest that, even though the relatively stable conditions of captivity allowed the studied females to maintain selective grooming interactions across time, small scale demographic changes affected the grooming dynamics of the group in accordance with the expectations of the Biological Markets theory. In particular, the maturation and consequent integration of a high ranking female into the group’s grooming network from one period to the next resulted in a more pronounced effect of rank on the regulation of grooming interactions. In addition, the influence of the maturation of a dependent infant on the grooming interactions of his mother were evident between periods. Our results also demonstrate that grooming networks are dynamic and that high ranking individuals are not necessarily the most central in grooming networks. Finally, we discuss the potential of social network analysis to identify cases of social exclusion and its consequences for captive management.
Highlights
In female kin-bonded Old World monkey species, the fitness of females has been shown to be positively affected by the formation and maintenance of strong, equitable and stable social bonds (Silk et al, 2010) with a few other specific females (Crockford et al, 2008; Silk et al, 2010; Brent et al, 2011)
Even though not all our predictions were fully supported, our results provide evidence of how grooming interactions are regulated among the females in a single matriline of mandrills
Our results suggest that female mandrills engage in grooming interactions with only a few partners, who are mostly maintained across time when demographic conditions remain relatively stable, that those interactions can be explained by the Biological Markets theory (BMT) and that grooming may be traded for social tolerance
Summary
In female kin-bonded Old World monkey species, the fitness of females has been shown to be positively affected by the formation and maintenance of strong, equitable and stable social bonds (Silk et al, 2010) with a few other specific females (Crockford et al, 2008; Silk et al, 2010; Brent et al, 2011). The BMT proposes that social interactions are based on the outcome of the exchange of social commodities in a marketplace and are regulated according to market forces (Hammerstein & Noë, 2016). It predicts that individuals favour the most reciprocal of their social partners according to the current demand and supply of commodities (Barrett et al, 1999; reviewed in: Hammerstein & Noë, 2016), such as tolerance (Barrett, Gaynor & Henzi, 2002), access to infants (Henzi & Barrett, 2002) or food (Fruteau et al, 2009). One key point of this model regarding the establishment of cooperative partnerships is that it posits that individuals can change their social partners if cooperating with other potential partners offers more benefits (Bshary & Noë, 2003)
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