Research examines coalition-building by Old World monkeys

Despite his yellow teeth, orange eyes and odd spiky ‘do, the crested black macaque is undeniably engaging, not the least to primatologist Maura Tyrrell, a PhD candidate in the UB’s Graduate Program in Evolution, Ecology and Behavior.

Intelligent and playful in their tiny-tailed, Old World monkey way, the males of this highly endangered species have been the subject of Tyrrell’s research since 2011.

She recently received a coveted research grant from the Leakey Foundation to support her 15-month study of social relationships between 20 wild adult male crested macaques (Macaca nigra) in different troops at the Tangkoko Nature Reserve on the Indonesian island of Sulawesi.

The Leakey Foundation is named for Louis and Mary Leakey, the great paleoanthropologists and archeologists who fostered field research of primates in their natural habitats, which they considered key to unraveling the mysteries of human evolution. To that end, it has supported the work of such primatologists as Dian Fossey and Jane Goodall, the latter of whom has long been a role model for Tyrrell.

In her research, Tyrrell is examining coalition behavior between crested black males in different competitive contexts with an eye to what they can tell us about the evolution of social structures.

“Coalition-building must have been very important in the development of the political and social structures of early humans,” Tyrrell says. “How, why and when these behaviors arose among primates may tell us something about later hominid (including human) social evolution.”

She explains that the M. nigra is one of 22 species of macaques, a genus of Old World monkeys, and are found only on Sulawesi and one other Indonesian island. They are in danger of extinction because of loss of habitat and their status as both agricultural pests and a popular bush meat. This is unfortunate because they have much to tell us.

“If I find that there are some elements of coalition behavior that are common to macaques, chimpanzees and humans,” she says, “it may be that some aspects of human coalitionary behavior have their origins in the common ancestors of Old World monkeys, apes and humans.”

Her mentor is the highly regarded primatologist Carol Berman, UB professor of anthropology and a specialist in macaques’ intricate social structures and behavior.

“Prior research has considered male coalition-building as a way to deal with competition within troops of nonhuman primates, but Maura is looking into the possibility that males also form coalitions to deal with incursions by outsiders,” Berman says.

Tyrrell began her observational studies with the crested black macaques in the Buffalo Zoo, whose behavior, she says, is very close to what it is in the wild. Three years later, she continued this work as a research assistant at the Macaca Nigra Project on Sulawesi, a collaborative venture between the German Primate Center and two Indonesian universities.

The Leakey Foundation grant will permit her to be back in Indonesia, testing her theses by following 20 male macaques in three habituated troops in their natural habitat for about 15 months.

“I want to create a clearer picture of social relationships among crested macaques to help broaden our understanding of how early human male alliances may have evolved,” Tyrrell says.

She explains the males and females of this species of macaque are sexually promiscuous, mate many times with many partners, and maintain separate dominance hierarchies. In this species’ troops, females will outnumber males by four or five to one. One might expect that finding a sexual partner would require little effort for a male, but that is not the case.

When young males mature, they leave their natal group to make their homes elsewhere, Tyrrell says. This practice is a boon to the sex lives of the older males and protects the troop’s gene pool, she explains, but in pursuit of their reproductive mandate, it means that young males have no access to the females in their natal domain.

To mate, they must invade another troop and make a bid to join it. They are not welcomed with open arms by the males in the new group, however, so they may live as solitary bachelors, usually for a brief time, before they maneuver their way into the hierarchy.

The migrating males appear to survey other groups to gather information about what is going on in those hierarchies before making their move, and seem to time their migrations to periods of instability, when the alpha male has been injured or a new alpha has recently taken over.

Once he fights his way into the troop, he then will have to maintain and improve his place in the new hierarchy to get access to the troop’s rosy-butted females. This process will involve regular physical contests with others in the group, as well as with outside males. It also may require complex forms of conflict resolution and coalition-building among his fellows. And this is Tyrrell’s research territory.

“In order to survive and procreate,” she says, “the males of some primate species have evolved into skillful conflict managers and manipulators of the male hierarchy. If they didn’t, they wouldn’t be passing on their genes anytime soon.

“I am interested in just what provokes conflict among the males and then how and why they make conciliatory gestures and signify the desire to build coalitions with other males,” she says.

“In multimale-multifemale primate groups in general, coalitions are formed for different reasons,” Tyrrell says. “High-ranking males may want to coalesce to confront lower-ranking males seeking to improve their chances in the mating game. Another reason is to deal with an external challenge, like new males attempting to join the troop. In this instance, the alpha male may initiate greeting behaviors that signal a desire for a coalition with other males in his troop as a way of indicating, ‘We’re all in this together.’”

Once they form their alliance, they may go after the newcomer — barking, staring, posturing, biting, chasing and other aggressive behaviors aimed at driving him away from the group and its females.

This is a serious business. Male M. Nigras are rarely related or have close affiliations to one another, so these encounters can be very violent, Tyrrell says, and can end in injury or death for one or more of the monkeys.

In either case, once the battle is over, there is a need to cool things down.

She explains that here are times when the encounter is so brutal, so life threatening that the opponents cannot reconcile and so will not be part of the same troop going forward.

Usually, however, after a violent fight the monkeys will come back together after a time and initiate friendly behavior — embracing or using affiliative gestures and postural displays — in an effort to make up with one another.  

“A black crested macaque may signal his willingness to make peace in other ways as well: by presenting his hind end to his former enemy, for instance, or by handling the other’s genitals (although this can be mutual),” she says. “Both are behaviors in which he exposes his vulnerability as if to demonstrate trust.”

If the invader wins, then he may take his place at the top of the hierarchy. If he loses his fight but is submissive after the fact, he may be permitted to take a place at the bottom of the social structure and work his way up, earning greater access to the females as he rises in rank. Similarly, if macaques have formed intra-troop coalitions to challenge the position of other macaques in the group, submissive behavior may be required of losers.  

“We can’t assume anything directly about human culture from this behavior,” she says, “but similar male affiliation behaviors are common in societies in which male cooperation is vital, as in those marked by military activities.”

Of her research, Tyrrell says: “My principle goal is to find out if behaviors used to manage conflicts between individuals — things like ‘reconciling’ after a fight, signaling friendly intentions, ritualized ‘greetings’ — are the same in different competitive contexts in which coalition-building is used.”