Diet-related factors strongly shaped the gut microbiota of Japanese macaques.

Although knowledge of the functions of the gut microbiome has increased greatly over the past few decades, our understanding of the mechanisms governing its ecology and evolution remains obscure. While host genetic distance is a strong predictor of the gut microbiome in large-scale studies and captive settings, its influence has not always been evident at finer taxonomic scales, especially when considering among the recently diverged animals in natural settings. Comparing the gut microbiome of 19 populations of Japanese macaques Macaca fuscata across the Japanese archipelago, we assessed the relative roles of host genetic distance, geographic distance and dietary factors in influencing the macaque gut microbiome. Our results suggested that the macaques may maintain a core gut microbiome, while each population may have acquired some microbes from its specific habitat/diet. Diet-related factors such as season, forest, and reliance on anthropogenic foods played a stronger role in shaping the macaque gut microbiome. Among closely related mammalian hosts, host genetics may have limited effects on the gut microbiome since the hosts generally have smaller physiological differences. This study contributes to our understanding of the relative roles of host phylogeography and dietary factors in shaping the gut microbiome of closely related mammalian hosts.

Male-male social bonds predict tolerance but not coalition formation in wild Japanese macaques.

Social bonds have been construed as differentiated and enduring affiliative relationships. Strong bonds will improve fitness through interchanging with coalition formation or tolerance over resources. Social bonds have been found in a variety of taxa and predict the formation of coalitions even amongst males. However, in species exhibiting steeply linear dominance hierarchies, coalitions are hypothesized to be suppressed due to severe competition amongst males, and thus strong bonds may manifest in other forms of behavior, notably social tolerance. The aim of this study was to examine the effects of male-male social bonds and dominance on agonistic supports and aggressive interaction in one of the most despotic primate species, Japanese macaques. I conducted focal samples on male individuals, recording their grooming, proximity to other members, agonistic supports and membership, and aggressive interactions over a 2-year observation period. Male macaques formed differentiated affiliative relationships across dyads and those relationships showed positive relations between the non-mating and the mating seasons. Steep dominance hierarchies were found amongst males. The occurrence of agonistic supports was not explained by the strength of social bonds but by the dominance of the participants, whereas strong bonds predicted less frequent aggressive interaction. These results are in line with the hypothesis that dominance is a major mechanism underlying coalition formation amongst males. Unlike more egalitarian species, strong bonds do not predict coalition formation but rather tolerance in despotic species. These results suggest male-male social bonds will bring alternative consequences according to dominance structures.

Social networks predict immigration success in wild Japanese macaques.

Male migration is common in mammals and comes with associated benefits and costs. Male-male affiliative relationships are behavioural strategies that migrating males can adopt in order to maximise benefits and minimize costs. While we know that such strategies primarily serve to reduce tension, little is known about how they actually affect male immigration success. We investigated the influence of male-male affiliative relationships on immigration success in a group of wild Japanese macaques (Macaca fuscata). We used social network analysis to examine the distribution of male-male affiliative interactions and their association with immigration success. We found that visiting males with high eigenvector centralities and low weighted degree centralities were more likely to be integrated into the group. Other factors such as season, age-class, and dominance rank amongst visiting males did not affect male integration success. Our results suggest that strong male affiliative bonds and a centralized position within the male-male grooming network can predict future integration success of visiting males into a social group through promoting higher tolerance of resident males and reducing aggression risks.

Sleeping site and tree selection by Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in Baihe Nature Reserve, Sichuan, China.

For non-human primates to optimize their survival chances, sleeping site selection is crucial as they spend much of their time sleeping. We studied sleeping site and tree selection by a group of wild Sichuan snub-nosed monkeys (Rhinopithecus roxellana) in the temperate forests of Baihe Nature Reserve, Sichuan, China, to assess if certain site and tree characteristics were selected. We identified a total of 39 sleeping sites and 111 sleeping trees over a period of 1 year. We compared nine sleeping site and six sleeping tree variables related to the environment, habitat, and vegetation structure. We found that certain characteristics of sleeping sites and sleeping trees predicted their selection by R. roxellana. On a larger spatial scale, sleeping sites were selected based mainly on four factors: canopy height, slope direction, slope gradient, and vegetation type. They also selected sites with trees that were taller and larger, had larger crown diameters and higher bole branches. On a smaller spatial scale, they selected larger trees with larger crown diameters. The selection of these characteristics could be explained in terms of predator avoidance and thermoregulation efficiency, although it was difficult to delineate which was more important. This could be due to some characteristics of R. roxellana, that is, large groups living in temperate climates, which required a balanced strategy for sleeping site and tree selection in order to optimize their survival chances.