Short-term separation from groups by male Japanese macaques: Costs and benefits in feeding behavior and social interaction

Development of an assessment method for freely moving nonhuman primates' eating behavior using manual and deep learning analysis

Purpose

Although eating is imperative for survival, few comprehensive methods have been developed to assess freely moving nonhuman primates' eating behavior. In the current study, we distinguished eating behavior into appetitive and consummatory phases and developed nine indices to study them using manual and deep learning-based (DeepLabCut) techniques.

Method

The indices were utilized to three rhesus macaques by different palatability and hunger levels to validate their utility. To execute the experiment, we designed the eating behavior cage and manufactured the artificial food. The total number of trials was 3, with 1 trial conducted using natural food and 2 trials using artificial food.

Result

As a result, the indices of highest utility for hunger effect were approach frequency and consummatory duration. Appetitive composite score and consummatory duration showed the highest utility for palatability effect. To elucidate the effects of hunger and palatability, we developed 2D visualization plots based on manual indices. These 2D visualization methods could intuitively depict the palatability perception and hunger internal state. Furthermore, the developed deep learning-based analysis proved accurate and comparable with manual analysis. When comparing the time required for analysis, deep learning-based analysis was 24-times faster than manual analysis. Moreover, temporal and spatial dynamics were visualized via manual and deep learning-based analysis. Based on temporal dynamics analysis, the patterns were classified into four categories: early decline, steady decline, mid-peak with early incline, and late decline. Heatmap of spatial dynamics and trajectory-related visualization could elucidate a consumption posture and a higher spatial occupancy of food zone in hunger and with palatable food.

Discussion

Collectively, this study describes a newly developed and validated multi-phase method for assessing freely moving nonhuman primate eating behavior using manual and deep learning-based analyses. These effective tools will prove valuable in food reward (palatability effect) and homeostasis (hunger effect) research.

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.

Inter-individual variation in the diet within a group of Japanese macaques and its relationship with social structure investigated by stable isotope and DNA analyses

We investigated individual variation in diet in relation to age-sex class and kin relationship in 28 of 40 members of a small group of wild Japanese macaques (Macaca fuscata). We used stable isotope ratios from hair as an index of individual dietary profiles, genetic relatedness as an index of kin relationship, and mitochondrial DNA (mtDNA) haplotype as a marker of being an immigrant or native member of the group. The range of carbon and nitrogen stable isotope ratios from hair of individual macaques (δ¹³C: -24.1‰ to -22.6‰, δ¹⁵N:3.8-5.5‰), which reflected their diet over a period of ~ 6 months, implied small individual variation in diet. The results of PERMANOVA implied that there were no significant effects of age class, sex, or mtDNA haplotype on hair stable isotope ratios between individuals, or on the variation in individual diet. However, the isotope values of males with mtDNA haplotypes that differed from those of the native females appeared to differ from those of other group members, which implies that immigrant males might have had a different diet profile from that of native group members. Furthermore, there was a weak correlation trend between genetic relatedness and differences in stable isotope ratios between pairs of individuals. Differences in stable isotope values were more marked in pairs with a more distant genetic relationship. This implies that within the group, closely related kin tended to forage together to avoid competing for food. However, this effect might have been weak because the size of the group was small relative to the size of the food patches, thereby reducing competition.

Association patterns and affiliative relationships outside a troop in wild male Japanese macaques, Macaca fuscata, during the non-mating season

In many mammals, males disperse more than females. Although males in some male-dispersing species form all-male groups, little is known about the association patterns or social relationships among them. Studies on male–male social relationships have primarily focused on competition over fertile females, but affiliative relationships among males have attracted much interest recently. I suggested a novel method for the classification of males based on their behaviour by principal component analysis (PCA), and investigated association patterns, and affiliative relationships in male Japanese macaques, Macaca fuscata, during the non-mating season. I observed 12 wild male Japanese macaques for 809 h during the non-mating season. The number of other animals within visual range, the amount of time that males spent in the vicinity of other animals, and the frequency of grooming interactions were examined. I classified males into two distinctive clusters (Cluster 1 and 2) according to their association and interaction patterns. Cluster 1 males associated with females and participated in grooming with them. Cluster 2 males had less visual encounters with females and did not groom them. Cluster 2 males showed proximity to other Cluster 2 males in all possible dyads. Although Cluster 2 males showed less proximity to each other than Cluster 1 males did, they frequently exchanged grooming among themselves. Cluster 2 males groomed Cluster 1 males more frequently than they were groomed by them. These results suggested that Cluster 1 were troop males, and Cluster 2 were non-troop males. Cluster 2 males had less opportunity for social interaction than Cluster 1 (troop) males, and they may form all-male groups. Males in all-male groups engaged in more frequent grooming than troop males. In addition, they groomed troop males more frequently than they were groomed. These results suggest that males could be separated by their behaviour. Male–male affiliative relationships might be influenced by within-group potential competition and imbalanced grooming appears to cause troop males to tolerate non-troop males which might be immigrated in near future.