The Development of Sociosexual Behaviours in Japanese Macaques Macaca Fuscata
Authors: Hanby Jeannette P. , Brown Conrad E. 
Published: April 2008

Sociosexual behaviours were observed over a two-year period in a natural troop of about 100 Japanese macaques (Macaca fuscata) confined in a two-acre corral. The development and mature expression of integrated patterns of mounting, presenting, thrusting, and related behaviours were examined. The frequency and type of mounting varied dramatically with the season of the year. Male-female, female-male, and female-female mounting were most frequent during the 6-month breeding season when males 4½ years and older can ejaculate and females 3½ years and older can conceive. Ejaculation generally occurred only after a series of mounts. Mountings in series by and on either sex were largely confined to the breeding season. Female presenting and male thrusting and certain other behaviours accompanied mounting more often at that time of year also. In the nonbreeding season, heterosexual interactions decreased but male-male mounting increased though it never reached breeding season levels for male-female mounting. Nonbreeding season mount events between both sexes and all ages typically involved only a single mount, but most were accompanied by thrusts. The type of interaction between pair members also differed; most mounting occurred during play. In males, mounting and thrusting were integrated gradually according to the season and sex of partner. By six months of age, males oriented to a partner's buttocks and used a double-foot-clasp posture on most mounts. At 1½ males mounted females more frequently than males and by 2½ showed the seasonal cycles in mount frequency and partner choice. They reached peaks in mount event frequency at 4½, but the most efficient and stable patterns were seen in males over 7 years of age. Although females showed thrusting movements early in life, they seldom mounted except on males during breeding season and occasionally during play or agonistic situations. They were most active as mount partners and actors after 3½ years of age. Their subsequent activity varied with the individual and her reproductive state. Several conclusions can be drawn from this and other studies on the development of sociosexual behaviours in primates. 1. Rearing conditions are crucial to the development and integration of postures, thrusting, intromission, and ejaculation. The most important element for normal development is the mother; however, the presence of other adult and encouraging females helps a young male to integrate the various elements. Peer males and females also facilitate or allow the expression of a variety of patterns and probably provide a source of enduring attachments and mature partner preferences. The role of the adult males in development is both positive and negative depending on the male, the group, and the species. 2. The most important aspect of normal sociosexual development is the differentiation and integration of elements such as mounting, presenting, thrusting, intromission into two patterns : the primarily copulatory and the primarily contacting. Intromission seems to be a key element in the differentiation process. Factors that facilitate intromission speed the process; factors that inhibit intromission delay the development of the young primate male's ability to distinguish correctly between postures, partners, and situations. The copulatory patterns of females seem less affected by unsatisfactory rearing conditions, but the sociosexual patterns of contact may be disturbed. 3. Mature sociosexual patterns develop from close physical contact with the mother or mother substitutes. Erection and thrusting appear independently but soon become linked to ventral clinging, embracing, riding, and mounting. Mount and present postures develop quickly and vary according to species and pairings and contexts. The most stereotyped posturing and patterns appear in the copulatory context: the sociosexual patterns retain their variability in form and variety of expression in different contexts, mainly affiliative and more rarely, agonistic,