Japanese macaques (Macaca fuscata) adjust inter-individual distance based on aggressiveness rather than rank differences

Group-living animals form societies structured around linear dominance hierarchies. However, social relationships within groups range from relaxed to tense, with some subordinates staying proximity of dominants, while others fleeing at their mere sight. Despite this variation, the effects of personality in shaping these relationships remains unclear. In this study, we investigated whether subordinates adjust their flight initiation distance (FID) according to the dominants aggressiveness. We collected video recordings of supplanting behaviours between non-kin dyads in Japanese macaques (Macaca fuscata). For each dyad, we evaluated these supplantings whether the subordinates FID was greater or less than two meters. To assess aggressiveness, we conducted 20-min focal observations of 18 females, recording of threats and aggressions. We calculated repeatability of aggressiveness as a measure of dominants personality. Rank differences were determined based on supplantings and aggressive interactions. As a result, aggressiveness showed high repeatability, independent of rank and sex. Subordinates were more likely to flee at greater distances (FID > 60 cm) when paired with more aggressive dominants. Rank difference did not significantly influence FID. Whether the dyads exhibiting FIDs were regular grooming partners did not significantly predict their FID. Our findings suggest that Japanese macaques adjust inter-individual distance not based on rank differences but in response to aggressiveness. These results highlight the importance of incorporating personalities into studies of primate social relationships.