Social Organization  
              Photograph courtesy of N. Rowe, The Pictoral Guide to Living Primates nrowe@primates.org  
                                           
  Japanese macaques live in multi-male, multi-female troops composed of between 40 and 194 members, sometimes as many as 700. If a troop becomes too large, it may split into two or more smaller troops (MacDonald 2001). Within a troop are several close family units including adult females and both male and female offspring, associated with a few central adult males (Grewal 1980).
                                           
  Their social organization is based on a stable linear dominance hierarchy. The most dominant individual is the alpha male, whose duties include directing troop movement and defending the troop. Two to three subleader males rank directly under him in the dominance structure, and their main responsibility is to maintain order within the troop. These duties can take the form of responding to calls for help from troop members, stopping fights, and chasing aggressive individuals. When the alpha male is nearby, the subleader males may seem unsure of whether to continue threatening aggressors or to let the alpha male handle the situation, thus demonstrating the alpha male's dominance over them. Next in the hierarchy are most of the adult females, whose main job is to protect and raise offspring. Female dominance is based on matrilineal inheritance, in which daughters inherit their mother's rank. Some matrilines are dominant over others, and though this ranking is stable over time, it can occasionally change. Infants and juveniles rank below the adult females. Finally, the rest of the adult males reside in the periphery of the group and rank last in the dominance hierarchy (Minnesota Zoo 2003). These males are usually a mixture of low ranking troop males (usually juvenile males between the ages of 3 and 6) and nomadic males that join a troop during non-mating season (MacDonald 2001; Yotsumoto 1976).
The dominance hierarchy in Japanese macaques can change based on social situations, a phenomenon called dependent rank. This ranking has influenced the way a troop organizes itself spatially, especially while feeding. The troop forms concentric circles, the center of which is occupied by leader males as well as adult females and their young. Subordinate males stay in the outside ring, partially because of social pressure by the dominant and subdominant males and adult females, which they exert in the form of attack. It has been suggested that this structure is due (at least in part) to alliance formation between troop members (Wantanabe 1979).
 
The mother is the primary care-giver of offspring, but the entire troop takes some measure of responsibility for the young. Mothers and offspring share the strongest type of social bond that exists in a troop. Sometimes adult offspring that remain in their natal troop will help their mother find food when she is too old to do so on her own (Beacham 1998).
 
           
Photograph courtesy of N. Rowe, The Pictoral Guide to Living Primates nrowe@primates.org          
                           
     

Grooming among Japanese macaques helps to maintain social bonds and to reconcile individuals after a conflict. The macaques communicate through various vocalizations (more than 30 of which have been recorded) as well as through facial and body expressions (Minnesota Zoo 2003).

 

  
                            Photograph courtesy of phototravels.net
As relatedness between individuals increases, the time they spend near one another or in physical contact increases. In addition, as relatedness increases between individuals, the amount of allogrooming they engage in increases. Kurland hypothesizes that allogrooming is primarily done for kin selection purposes. However, he states that grooming probably also has other "manipulatory" purposes, such as in mating behavior (Kurland 1977).

Mothers groom male offspring more often than female offspring. Because male reproductive success is quantitatively higher than that of females, mothers increase their own inclusive fitness by caring for their male offspring more closely than their female offspring. However, once juvenile females reach 2 years of age, mothers and daughters have a reciprocal grooming relationship that mothers and sons rarely ever have (Kurland 1977).

Older siblings groom their younger siblings more often than the younger siblings groom their older siblings. Likewise, mothers groom their young offspring more frequently than the offspring groom their mothers. However, in less related pairs, both individuals groom equally. Kurland hypothesizes that this non-reciprocal grooming behavior indicates that there is a selection pressure that influences older macaques to be more altruistic and younger macaques to be more selfish. This arrangement would allow the younger individuals to have a higher rate of survival and the older individuals to increase their inclusive fitness by aiding that survival (Kurland 1977).

Grooming between grandmothers and granddaughters has been observed and is considered to be reciprocal altruism. The granddaughter grooms her grandmother more frequently, and the grandmother defends her granddaughter from predators and other monkeys in return (Kurland 1977).
Females
Female young spend much of their time grooming their mother and sisters, which helps to reinforce their social bonds (Minnesota Zoo 2003). After sexual maturity, female young remain in the troop, and their bonds with one another (especially with members of their own matriline) remain strong throughout their lives (Koyama 1967, 1970, as cited in Grewal 1980). These kinship groups often care for sick and injured individuals, including those with birth defects (Beacham 1998).
Female relationships in troops of Japanese macaques are generally more stable (though not immutable) than those of males. One observation that supports this claim is that troop fissions usually occur along matrilineal lines. However, it has been suggested that the rank of alpha female may be subject to competition, as is the rank of alpha male. After observing the Arashiyama West troop (the troop that has been transplanted to Texas), one primatologist reports that the alpha female was challenged and displaced by a mid-ranking female of a different matriline. After this rank change took place, the female kin of the former and the new alpha females also changed ranks, and the kin of the new alpha female claimed dominance over the previous alpha female and her kin (Gouzoules 1980).
Males    
Male offspring spend less time with their mothers than female young do, preferring to rough-house in play groups composed of males around the same age (Minnesota Zoo 2003). Once they reach sexual maturity (usually between the ages of 3 and 7 years), they emigrate from the troop (Sugiyama 1976, as cited in Grewal 1980) and are free to migrate between troops throughout the rest of their lives (Macdonald 2001). Because juvenile males have been observed living in troops very geographically close to their natal troop, it is not believed that this emigration is due to a tendency for juvenile males to travel far away from their natal group. Instead, male emigration is thought to be an inbreeding-avoidance mechanism, maximizing genetic diversity by preventing them from mating with their mothers, sisters, and other female kin. In addition, if juvenile males remained in their natal troop, there would be fewer females with whom they could mate (barring their natal matriline, which will not mate with male relatives), and would thus be at a reproductive disadvantage (Enomoto 1974, as cited in Grewal 1980).
 
  The main difference between the Japanese macaque multi-male, multi-female organization and a one-male-unit is the existence of several adult central males that live with a great degree of tolerance for one another (Eisenberg, Muckenhirn & Rudran 1972, as cited in Grewal 1980), a phenomenon that is necessary partly because of the large size of the troops. Duties of the central males include protecting the troop from predators and other outside threats, mediating aggression within the troop, stabilizing social relationships, maintaining the home range, and leading troop movement. Without several males performing these duties, the troop would most likely be unable to exist in such high numbers due to increased aggression (Grewal 1980). However, when space requirements are not met (as in the transplanted Oregon troop that is kept in a .8 ha enclosure), males and other troop members are less tolerant of one another and are more aggressive despite central males' attempts to control the group (Alexander & Bowers 1968, as cited in Clark 1978).
  Photograph courtesy of phototravels.net
             
Some cases of central males caring for young have been documented in the Arashiyama troop (Itani 1959 and Alexander 1970, as cited in Grewal 1980). Adult males have demonstrated strong ties to one or two juvenile females (less than 2 years of age), but these ties dissipated once the juveniles aged to maturity. Most of these interactions occurred with orphaned juveniles or with juveniles who were part of a kingroup with which the particular central male had high levels of interaction (Grewal 1980).
Grooming activities in the Arashiyama troop between central males and members of various kinship groups have been observed. However, no correlation has been found between a central male's rank or age and the time he spent in grooming activities. In all reported observations, central males engaged in grooming behaviors with individuals from more than one kinship group, and members of one kinship group usually engaged in grooming activities with more than one central male. In addition, there was no correlation between the rank of a central male and the rank of the kinship group with which he engaged in the most contact (Grewal 1980).
Proximity relations between central males and other individuals in the Arashiyama troop have also been recorded. No correlation was found between the rank or age of a central male and the time he spent near other individuals. Proximity interactions of central males changed to different kin groups from year to year (and likewise, the kin groups' proximity interactions changed to different central males from year to year). Direct contact between males is infrequent because males are generally less social than females (Kurland 1977), but they are indirectly associated with one another through their independent interactions with the same kin groups. Bonds between a kinship group and central males seem to be especially important during times of troop division. Instability within a troop prior to fission may be caused by kin groups limiting themselves to interactions with only a few adult males. In addition, loosening such bonds with all central males can cause a female kingroup to be isolated from the rest of the troop, resulting in its desertion from the troop (Sugiyama 1960, Koyama 1970, Missakian 1973, Chepko-Sade 1974 as cited in Grewal 1980). It is inferred from these observations that association with at least one central male is imperative for a kingroup to remain bound to a troop (Grewal 1980).
               
    Associations between central males and adult females during non-mating season are usually continuations of associations established during the mating season. Sexual relations are believed to be very important in breaking male-female bonds from the previous mating season and forming new ones that will shape a troop's social relations during the subsequent non-mating season (Grewal 1980).        
               
Photograph courtesy of phototravels.net  
The alpha female tends to travel and socialize with the alpha male, and she frequently assists him in his agonistic encounters. The alpha male often aids the alpha female in her agonistic encounters as well, resulting in a mutually beneficial relationship. Some observations have indicated that the alpha male can be dependent upon the alpha female and her kin to maintain his dominant position (Bernstein 1969, Kawamura 1967, Neville 1968, as cited in Gouzoules 1980), and it is possible that the alpha female depends on the alpha male in the same manner (Gouzoules 1980).
     
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