Spatial position-associated mating strategies employed by male Japanese macaques (Macaca fuscata yakui) in Yakushima

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.

Dominance rank, female choice, and reproductive success in semi-free ranging adult male Japanese macaques (Macaca fuscata)

The assumed evolutionary advantage of dominance is increased reproductive success. However, the efficacy of dominance as a mating strategy may be interrupted by any number of variables including female choice, estrous synchrony, and mating by non-troop males. In Japanese macaques (Macaca fuscata), there is evidence both for and against dominance as conferring reproductive success for adult males, with many discussions pointing to the importance of female choice in governing reproductive success in certain populations. In this study, we aimed to evaluate dominance-based versus female choice-based male behavioral strategies and their impact on reproductive success. This study was conducted on a group of Japanese macaques at the Oregon National Primate Research Center. We collected a total of 512 h of behavioral data across two summer study periods in 2018 and 2019. We conducted 15-min focal follows with 1-min instantaneous scans on 17 adult males. Reproductive data were available from genetic records. Using principal components analysis (PCA), we identified males that cluster according to similar behavioral strategies. We then used analysis of variance (ANOVA) and non-parametric ANOVA on ranks to ascertain significant variation in rank and reproductive success between clusters. We found that males that clustered based on high directed aggression held higher rank than less-aggressive male clusters (F = 27.21, df = 4, p < .0001). However, less aggressive male clusters had higher reproductive success (F = 3.50, df = 4, p = .04). There was no variation between affiliative clusters in reproductive success (F = 1.77, df = 3, p = .15). The highly aggressive strategy is effective for attaining high rank, but only resulted in high reproductive success for a single male which likely necessitates alternative strategies. We suggest the operation of female choice within this population, with females preferentially mating with males who are not only affiliative but also less aggressive.