The influence of phylogeny, social style, and sociodemographic factors on macaque social network structure

Abstract

Among nonhuman primates, the evolutionary underpinnings of variation in social structure remain debated, with both ancestral relationships and adaptation to current conditions hypothesized to play determining roles. Here we assess whether interspecific variation in higher-order aspects of female macaque (genus: Macaca) dominance and grooming social structure show phylogenetic signals, that is, greater similarity among more closely-related species. We use a social network approach to describe higher-order characteristics of social structure, based on both direct interactions and secondary pathways that connect group members. We also ask whether network traits covary with each other, with species-typical social style grades, and/or with sociodemographic characteristics, specifically group size, sex-ratio, and current living condition (captive vs. free-living). We assembled 34-38 datasets of female-female dyadic aggression and allogrooming among captive and free-living macaques representing 10 species. We calculated dominance (transitivity, certainty), and grooming (centrality coefficient, Newman's modularity, clustering coefficient) network traits as aspects of social structure. Computations of K statistics and randomization tests on multiple phylogenies revealed moderate-strong phylogenetic signals in dominance traits, but moderate-weak signals in grooming traits. GLMMs showed that grooming traits did not covary with dominance traits and/or social style grade. Rather, modularity and clustering coefficient, but not centrality coefficient, were strongly predicted by group size and current living condition. Specifically, larger groups showed more modular networks with sparsely-connected clusters than smaller groups. Further, this effect was independent of variation in living condition, and/or sampling effort. In summary, our results reveal that female dominance networks were more phylogenetically conserved across macaque species than grooming networks, which were more labile to sociodemographic factors. Such findings narrow down the processes that influence interspecific variation in two core aspects of macaque social structure. Future directions should include using phylogeographic approaches, and addressing challenges in examining the effects of socioecological factors on primate social structure.

Social Interactions Between Rhesus Macaques (<i>Macaca mulatta</i>) and Assamese Macaques (<i>M. assamensis</i>) in Nepal: Why Do Male Rhesus Macaques Follow Social Groups of Assamese Macaques?

“…Both species are seasonal breeders, and rhesus and Assamese macaque females give birth from April to July and from March to July, respectively (Ogawa, unpublished data). Compared with the rhesus macaque, however, the Assamese macaque is more arboreal, frequently staying in the higher canopy and on cliffs, has a larger body, is less kin biased, and has a more relaxed dominance style (Balasubramaniam et al, 2018;Koirala et al, 2017;Zhou et al, 2014).…”

Tibetan Macaque Social Style: Covariant and Quasi-independent Evolution

“…Phylogeographic Approaches Finally, comparative studies have now established that several (but not all) aspects of macaque social structure (Balasubramaniam et al 2012a(Balasubramaniam et al , 2018aThierry et al 2008), and more broadly primate sociality (Kamilar and Cooper 2015), are associated at least in part with species' ancestral relationships. What is unclear is whether such phylogenetic signals are reflections of true genetic linkage or coevolution versus artifacts of adaptive responses by ancestral species to major environmental changes (Balasubramaniam et al 2018a).…”

“…Phylogeographic Approaches Finally, comparative studies have now established that several (but not all) aspects of macaque social structure (Balasubramaniam et al 2012a(Balasubramaniam et al , 2018aThierry et al 2008), and more broadly primate sociality (Kamilar and Cooper 2015), are associated at least in part with species' ancestral relationships. What is unclear is whether such phylogenetic signals are reflections of true genetic linkage or coevolution versus artifacts of adaptive responses by ancestral species to major environmental changes (Balasubramaniam et al 2018a). To address this gap, we recommend that future research should focus on establishing links between ancestral state reconstructions of primate social structure (Pagel et al 2004;Revell 2012) and potential changes in historic phylogeographic ranges (Abegg and Thierry 2002;Lemey et al 2009;Ree and Smith 2008).…”

A multilevel statistical toolkit to study animal social networks: Animal Network Toolkit (ANT) R package

“…In animal research, it remains difficult to analyze this type of metrics because several of them are strongly dependent with a basic metric called density (network ratio of observed links to all potential links). Density is sensitive to the sampling effort which in turn is linked to group size, making then very difficult to compare global metrics of different networks with no specific analytical protocol established [27][28][29]. All the global metrics available in ANT are synthesized in Table I.…”