The effect of solicitations on grooming exchanges among female Japanese macaques at Katsuyama

Opportunistic availability of an infant and social relationship to a mother influence grooming before infant handling in Japanese macaques

Biological market theory (BMT) predicts that the balance between supply and demand determines the economic value of a "commodity," which consequently determines the amount of "services" that an individual needs to provide to obtain the commodity. In infant handling among primates, the existing literature suggests that handlers need to groom a mother to obtain access to its infant, particularly when the value of the infant is high (e.g., when the number of infants is low). However, grooming by handlers may not be a prerequisite for the occurrence of infant handling, because handlers can handle an infant that is separated from its mother. Based on 3 years of behavioral observations of wild Japanese macaques (Macaca fuscata), we examined the process by which infant handling occurs and the role of grooming in infant handling. We found that infant handling occurred more frequently when the mother and infant were separated than when they were in contact. Grooming rarely occurred before infant handling. The subsequent occurrence of infant handling was not predicted by either the occurrence or duration of grooming toward mothers by non-mother individuals. Grooming by handlers was also more likely to occur when an infant was in contact with its mother and when an infant's mother was dominant to the handlers. Contrary to BMT, the number of infants in a group did not affect grooming by handlers. These results indicate that the handlers' decision to groom depended on the opportunistic availability of an infant and the social relationship between the infant's mother and themselves. We conclude that grooming was not always necessary for infant handling.

Triadic grooming among adult females in a free-ranging group of Japanese macaques

This study aimed to quantitatively describe triadic grooming bouts in a free-ranging group of Japanese macaques (Macaca fuscata). Two types of triadic grooming bouts occurred less frequently and for a shorter duration than dyadic grooming bouts: straight-line type (SL), where individual A grooms B, who then grooms C; and two-to-one type (TO), where individuals X1 and X2 groom Y. TO-type grooming was recorded more often than SL-type grooming. As in the dyadic grooming bouts, two females who had direct grooming interactions in both SL-type (i.e., between A and B or between B and C) and TO-type groomings (i.e., between X1 and Y and between X2 and Y) and two groomers who did not have direct grooming interactions in TO-type grooming were closely related to each other in more than the half of the pairs recorded. Groomers were more likely to be subordinate to groomees in triadic grooming. Almost all of the observed pairs in SL- and TO-type groomings were also recorded in dyadic grooming bouts. These findings indicate that like dyadic grooming, triadic grooming bouts are largely influenced by blood relatedness through maternal lines and dominance relationships between participants. Based on affiliative relationships maintained through dyadic grooming, triadic grooming could be influenced by such affiliative relationships and then function to strengthen bonds between participants. Possible relationships between triadic grooming and the level of social tolerance among individuals are discussed from the viewpoints of interspecies differences among macaque species and regional differences in Japanese macaques.

Low-ranking female Japanese macaques make efforts for social grooming

Grooming is essential to build social relationships in primates. Its importance is universal among animals from different ranks; however, rank-related differences in feeding patterns can lead to conflicts between feeding and grooming in low-ranking animals. Unifying the effects of dominance rank on feeding and grooming behaviors contributes to revealing the importance of grooming. Here, I tested whether the grooming behavior of low-ranking females were similar to that of high-ranking females despite differences in their feeding patterns. I followed 9 Japanese macaques Macaca fuscata fuscata adult females from the Arashiyama group, and analyzed the feeding patterns and grooming behaviors of low- and high-ranking females. Low-ranking females fed on natural foods away from the provisioning site, whereas high-ranking females obtained more provisioned food at the site. Due to these differences in feeding patterns, low-ranking females spent less time grooming than high-ranking females. However, both low- and high-ranking females performed grooming around the provisioning site, which was linked to the number of neighboring individuals for low-ranking females and feeding on provisioned foods at the site for high-ranking females. The similarity in grooming area led to a range and diversity of grooming partners that did not differ with rank. Thus, low-ranking females can obtain small amounts of provisioned foods and perform grooming with as many partners around the provisioning site as high-ranking females. These results highlight the efforts made by low-ranking females to perform grooming and suggest the importance of grooming behavior in group-living primates.