Benefits of Social Grooming in Wild Chimpanzees: Hormone Oxytocin Facilitates Cooperation

Jan. 23, 2013 — Animals which maintain cooperative relationships show gains in longevity and offspring survival. However, little is known about the cognitive or hormonal mechanisms involved in cooperation. Researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have now found that cooperative relationships are facilitated by an endocrinological mechanism involving the hormone oxytocin, even when these are between non-kin.


They collected urine samples of 33 chimpanzees from Budongo Forest, Uganda, and measured their urinary oxytocin levels after single episodes of a specific cooperative behavior, mutual grooming. The result: Oxytocin levels were higher after grooming with cooperation partners compared with non-cooperation partners or after no grooming, regardless of genetic relatedness or sexual interest. This suggests that in chimpanzees oxytocin, which acts directly on neural reward and social memory systems, plays a key role maintaining social relations beyond genetic ties and in keeping track of social interactions with multiple individuals over time.

In non-human primates and other social animals strong and enduring social bonds are typically seen between genetically related individuals but also, occasionally, between non-kin, same-sex individuals. Although such relationships are typically defined by high rates of cooperative behaviors, how they are maintained over time is still unclear. In humans and other social mammals the neuropeptide hormone oxytocin plays a central role in facilitating bonding between kin and mating partners. Catherine Crockford, Roman Wittig and colleagues of the Max Planck Institute for Evolutionary Anthropology have now analyzed the role of this hormone in the social relationships between wild chimpanzees.

To this end the researchers observed social interactions – like mutual grooming – in a group of wild chimpanzees from Budongo Forest in Uganda and non-invasively collected urine samples of the 33 female and male adult group members on plastic bags or leaves. They determined the level of the hormone oxytocin before and shortly after the animals had been grooming with each other and found that oxytocin levels were especially high in chimpanzees who had been grooming with a “bond partner”,  a cooperation partner, irrespective of whether this bond partner happened to be their kin or not. On the other hand, the level of urinary oxytocin was much lower in chimpanzees who had been grooming with a “non-bond partner”, with whom they did not share a cooperative relationship, or in animals who had not been grooming at all. Furthermore, the researchers found that the animal’s sex or age, grooming duration and other factors did not have a significant influence on urinary oxytocin levels.

“Our results demonstrate that a rise in oxytocin was dependent upon the combined effects of social grooming with a bond partner”, says Catherine Crockford of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “Crucially, oxytocin levels were similarly high after grooming with non-kin and kin bond partners. This suggests that, in chimpanzees, oxytocin plays a key role in maintaining social relations beyond immediate genetic ties”.

“This is the first study that measures the levels of the hormone oxytocin on wild animals in a non-invasive way”, says Roman Wittig of the Max Planck Institute for Evolutionary Anthropology. “We have developed a tool with which cross-species comparisons that link underlying physiology and behavior can eventually be made of social mammals in their natural environment”. In future field research this tool will be used to compare single behaviors – like other cooperative  or aggressive behaviors–by measuring how they differ from each other hormonally.

 

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The above story is reprinted from materials provided byMax-Planck-Gesellschaft.

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Journal Reference:

  1. C. Crockford, R. M. Wittig, K. Langergraber, T. E. Ziegler, K. Zuberbuhler, T. Deschner. Urinary oxytocin and social bonding in related and unrelated wild chimpanzees.Proceedings of the Royal Society B: Biological Sciences, 2013; 280 (1755): 20122765 DOI: 10.1098/rspb.2012.2765
Max-Planck-Gesellschaft (2013, January 23). Benefits of social grooming in wild chimpanzees: Hormone oxytocin facilitates cooperation. ScienceDaily. Retrieved January 28, 2013, from http://www.sciencedaily.com/releases/2013/01/130123094251.htm

Primate Behavior: Chimps Select Smart Tools, Monkeys Intentionally Beg

ScienceDaily (July 18, 2012) — Chimpanzees use weight to pick the best tool, and monkeys beg more when they’re paid attention to, as reported in two independent research reports published July 18 in the open access journal PLoS ONE.


In the chimp study, researchers found that the chimpanzees used weight to choose the best hammer to crack open nuts. Nut cracking is one of the most sophisticated instances of tool use in chimpanzees, and learning how to do it has been shown to be very difficult for some chimps. In work led by Cornelia Schrauf of the University of Vienna, the researchers showed that the chimps were able to choose the best tool to crack nuts based solely on the weight of the tool. Schrauf notes, “Experience clearly affected the subjects´ attentiveness to the relevant tool properties. Whereas the most skilled chimpanzee showed a preference for the most efficient hammers from the early beginning of the experiment, the unskilled individuals became selective over time.”

In another study, old world monkeys called Mangabeys were shown to modulate their begging behavior based on whether the experimenter was paying attention to them. The monkeys were trained to make “requesting gestures,” and the researchers, led by Audrey Maille of the University of Rennes 1 in France, found that the monkeys gestured more and faster when the experimenter’s body and head were facing the monkey than when they were oriented away. The monkeys did not modulate their behavior simply based on the direction of the experimenter’s gaze, though.

Maille explains, “Our study deals with…whether functional similarities may be found between human language and nonhuman primates communication. By investigating the flexibility of gestures production, we showed that old world monkeys, and not only great apes, may use communicative signals intentionally.”

 

Journal References:

  1. Maille A, Engelhart L, Bourjade M, Blois-Heulin C. To Beg, or Not to Beg? That Is the Question: Mangabeys Modify Their Production of Requesting Gestures in Response to Human’s Attentional States. PLoS ONE, 2012; 7 (7): e41197 DOI: 10.1371/journal.pone.0041197
  2. Schrauf C, Call J, Fuwa K, Hirata S. Do Chimpanzees Use Weight to Select Hammer Tools? PLoS ONE, 2012; 7 (7): e41044 DOI: 10.1371/journal.pone.0041044

 

Public Library of Science (2012, July 18). Primate behavior: Chimps select smart tools, monkeys intentionally beg. ScienceDaily. Retrieved July 19, 2012, from http://www.sciencedaily.com­ /releases/2012/07/120718192005.htm