Activity and social factors affect cohesion among individuals in female Japanese macaques: A simultaneous focal-follow study

Emergent centrality in rank-based supplanting process

We propose a stochastic process of interacting many agents, which is inspired by rank-based supplanting dynamics commonly observed in a group of Japanese macaques. In order to characterize the breaking of permutation symmetry with respect to agents' rank in the stochastic process, we introduce a rank-dependent quantity, overlap centrality, which quantifies how often a given agent overlaps with the other agents. We give a sufficient condition in a wide class of the models such that overlap centrality shows perfect correlation in terms of the agents' rank in the zero-supplanting limit. We also discuss a singularity of the correlation in the case of interaction induced by a Potts energy.

Seasonal responses and host uniqueness of gut microbiome of Japanese macaques in lowland Yakushima

Background

Changes in the gut microbial composition is an important response to cope with the seasonal fluctuations in the environment such as food availability. We examined the bacterial gut microbiome of the wild nonhuman primate, Japanese macaque (Macaca fuscata) in Yakushima over 13 months by noninvasive continuous sampling from three identified adult females.

Results

Dietary composition varied considerably over the study period and displayed marked shifts with the seasons. Feeding of leaves, fruits, and invertebrates were their main foods for at least one month. Diet had a significant influence on the gut microbiome. We also confirmed significant effect of host uniqueness in the gut microbiome among the three macaques. Leaf-dominated diet shaped unique gut microbiome structures where the macaques had the highest alpha diversity and their gut microbiome was enriched with Spirochaetes and Tenericutes. Diet-related differences in the putative function were detected, such as a differentially abundant urea cycle during the leaf-feeding season.

Conclusion

Both diet and host individuality exerted similar amounts of effect on gut microbe community composition. Major bacterial taxa showed a similar response to monthly fluctuations of fruit and invertebrate feeding, which was largely opposite to that of leaf feeding. The main constituents of fruits and invertebrates are both digestible with the enzyme of the host animals, but that of leaves is not available as an energy source without the aid of the fermentation of the gut microbiome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42523-022-00205-9.

Fission-fusion dynamics in a wild group of Japanese macaques (Macaca fuscata) on Kinkazan Island caused by the repeated separation of an alpha male being followed by females

The spatiotemporal cohesion of a group is an essential element of primate society. It is thus important to clarify the factors that influence the extent of variation in spatial cohesion and individual membership in a group over time, known as fission-fusion dynamics. During the mating season of 2019, the alpha male (TY) in a wild group of Japanese macaques on Kinkazan Island repeatedly disappeared from the group, and we observed fission-fusion dynamics caused by his movement. The group seemed to have split when TY left the group or its home range, and females who followed him had the most affiliative relationships with TY or were the relatives of those females. Although TY disappeared from the group in the post-mating season, these fission-fusion dynamics only occurred during the mating season probably because females had a more substantial need for protection against aggression from the other males during the mating season. These results indicate that, although rare, fission-fusion dynamics based on affiliative relationships between males and females can occur with the separation of alpha males from the group. More studies in other populations are needed to clarify the influence of group males on the spatial cohesion of groups.

Activity synchrony and travel direction synchrony in wild female Japanese macaques

The degree of behavioural synchrony of animals within a group can be considered a reflection of how individuals adjust their behaviours to manage the costs/benefits accompanying group-living. In this study, we focused on activity synchrony and travel direction synchrony as behavioural synchrony. We aimed to quantify the degree of behavioural synchrony and identify which factors can affect the synchrony in wild females of Japanese macaques. Japanese macaques live in female philopatric multi-female and multi-male groups and have a linear dominance hierarchy. The groups are characterized by changing spatio-temporal cohesiveness among group members. Two observers conducted simultaneous focal animal sampling on adult females using global positioning system devices to record locations. The overall degree of activity synchrony was positive compared with random, and the degree was highest when macaques were located within visual range of each other. Both activity synchrony and travel direction synchrony were influenced by spatial cohesion, i.e. interindividual distance, which shows that the probabilities of synchrony were higher with individuals located closer. Activity synchrony was also influenced by activity type, showing that the probabilities of synchrony were higher when individuals engaged in foraging. These results suggest that synchronized foraging may be caused by enhanced feeding with other group members when they are closer to each other. Our approach to quantitatively measure spatial dispersal while observing group members simultaneously revealed the roles of spatial cohesion and activity types for determining the degree of behavioral synchrony.

Behavioral Causes, Ecological Consequences, and Management Challenges Associated with Wildlife Foraging in Human-Modified Landscapes

Humans have altered up to half of the world's land surface. Wildlife living within or close to these human-modified landscapes are presented with opportunities and risks associated with feeding on human-derived foods (e.g., agricultural crops and food waste). Understanding whether and how wildlife adapts to these landscapes is a major challenge, with thousands of studies published on the topic over the past 10 years. In the present article, we build on established theoretical frameworks to understand the behavioral causes of crop and urban foraging by wildlife. We then develop and extend this framework to describe the multifaceted ecological consequences of crop and urban foraging for the individuals and populations in which they arise, with emphasis on social species for which interactions with people are, on balance, negative (commonly referred to as raiding species). Finally, we discuss the management challenges faced by urban and rural land managers, businesses, and government organizations in mitigating human-wildlife conflicts and propose ways to improve the lives of both wildlife and humans living in human-modified landscapes and to promote coexistence.

Behavioral responses of Japanese macaques to playback-simulated intergroup encounters

Group-living animals gain fitness benefits from intergroup aggression, but also incur costs. Advertisement behaviors, such as long-distance calls and scent marking, help animals avoid disadvantageous, or less rewarding, fights. However, it remains unclear how species that lack advertisement behaviors respond to auditory information from other groups. We hypothesized that such species use auditory information prior to visual contact with the opponent group to determine its relative resource holding potential. Here, we aimed to identify the behavioral responses of Japanese macaques to simulated intergroup encounters. We conducted a vocal playback experiment and behavioral observations of 11 adult males and females from two groups intermittently from October 2015 to June 2017. In response to vocalizations of other groups, the macaques stopped feeding, decreased contact calling, and increased visual scanning, which could enable them to make timely and accurate decisions as to whether to fight or flee. The spatial cohesion of the group did not change. These results partly support our hypothesis and suggest that the onset of increased vigilance to opponents is prior to visual contact with them. The present study highlights the importance of investigating early phases of intergroup encounters in species lacking advertisement behaviors to obtain new insights on intergroup conflicts in animals.

Variations in within-group inter-individual distances between birth- and non-birth seasons in wild female patas monkeys

Individual spatial positioning plays an important role in mediating the costs and benefits of group living, and thus shapes different aspects of animal social systems including group structure and cohesiveness. I aimed to quantify variation in individual spacing behavior and its correlates in a group of wild patas monkeys (Erythrocebus patas) living in north Cameroon. I collected data on inter-individual distances during group scans when following subject females. Individuals had longer inter-individual distances during the non-birth season than during the birth season. Dominance relationships had little effect on inter-individual distances between females during both the non-birth and birth seasons. The results suggest that group cohesion was higher during the birth season than the non-birth season. Thus I conclude that higher group cohesion during the birth season may reduce the predation risk of infants.

Rudimentary empathy in macaques' social decision-making

Primates live in highly social environments, where prosocial behaviors promote social bonds and cohesion and contribute to group members' fitness. Despite a growing interest in the biological basis of nonhuman primates' social interactions, their underlying motivations remain a matter of debate. We report that macaque monkeys take into account the welfare of their peers when making behavioral choices bringing about pleasant or unpleasant outcomes to a monkey partner. Two macaques took turns in making decisions that could impact their own welfare or their partner's. Most monkeys were inclined to refrain from delivering a mildly aversive airpuff and to grant juice rewards to their partner. Choice consistency between these two types of outcome suggests that monkeys display coherent motivations in different social interactions. Furthermore, spontaneous affilitative group interactions in the home environment were mostly consistent with the measured social decisions, thus emphasizing the impact of preexisting social bonds on decision-making. Interestingly, unique behavioral markers predicted these decisions: benevolence was associated with enhanced mutual gaze and empathic eye blinking, whereas indifference or malevolence was associated with lower or suppressed such responses. Together our results suggest that prosocial decision-making is sustained by an intrinsic motivation for social affiliation and controlled through positive and negative vicarious reinforcements.