Chimpanzees Need Friends Too -- Their Stress Levels Show It
A little social support from your best buds goes a long way, whether you're a human or a chimp. A new study that followed a chimpanzee community in the forests of Uganda has found that quality time with close companions significantly decreased stress hormone levels in the primates -- whether they were resting, grooming or facing off against rival groups.
The findings, described in the journal Nature Communications, shed light on the physiological effects of close companionship in chimps -- and could have implications for human health too.
Researchers have long known that stress can worsen health and raise the risk of death in humans as well as other social mammals.
"It can have effects on immune function, cardio function, fertility, cognition, even your mood," said study coauthor Kevin Langergraber, a primatologist at Arizona State University.
It also has become clear that maintaining close social bonds can help these types of animals (humans included) to buffer some of that stress -- and thus, perhaps mitigate some of those health risks. But scientists have yet to pin down, physiologically, exactly what mechanisms are at work here.
"Social bonds make you survive and produce better -- but how do they do that?" Langergraber said.
To find out, the international team of researchers studied members of the Sonso chimpanzee community in Uganda's Budongo Forest -- a group consisting of 15 males, 35 females and 28 juveniles and infants during the study period from February 2008 to July 2010.
Like humans, chimpanzees tend to have besties -- bond partners with whom they appeared to feel close. (Just as some humans might have one or two close friends and others have more, the number of bond partners varied for each chimp.) The researchers wanted to see whether interactions with these bond partners led to lower stress levels during particularly stressful situations (such as when fighting rival groups) or whether it helped lower those levels at any time.
The scientists observed the chimps perform three types of activities: resting, grooming or inter-group squabbles (which happened either when the chimps heard or saw a rival group, or when the researchers banged on the large buttress roots of nearby trees -- which caused the chimps to react aggressively as if they'd heard a rival group). They watched to see whether the chimps were doing any of these three things with their bond partners or with other chimps in their group to which they were not as close.
A team of up to six observers watched the activities of three parties of chimps and then followed them around collecting urine samples. They then would test their levels of urinary glucocorticoids in order to evaluate the amount of the stress hormone cortisol.
This, by the way, was no task for the faint of heart. It involved following individual chimps for six hours after observing one of the three activities, and, while recording every change in behavior, getting up close and personal with the animals' bodily fluids.
"Urine was either pipetted from plastic bags, after the bags were tied over a forked stick and held in the urine stream when subjects were sitting in a tree, or from leaf matter when urination occurred on the ground after subjects had moved away," the study authors wrote. "After collection, urine samples were stored in a thermos flask containing ice and were frozen in liquid nitrogen upon arrival in camp, which was within 10 h after collection."
And yes, in case you were wondering, the observers did sometimes get splashed.
"Sometimes you [end up] collecting a little bit of the sample in your face, and wherever else, and that's not ideal," Langergraber said.
The scientists found that chimpanzees' urinary glucocorticoid, or uGC, levels were significantly lower during the activities when they were with their bond partner -- notably stressful activities, such as the intergroup rivalries, where any chimp on the front line, barking out threats at the rival chimps, might face physical harm or even death.
"Subjects participating in events with bond partners rather than other individuals had on average 23% lower relative uGC levels, across events," the study authors wrote.
The findings dovetail well with earlier research showing that levels of oxytocin -- the so-called "cuddle hormone" -- go up during grooming, Langergraber said.
"It might be indicating that oxytocin might have a dampening role in cortisol secretions ... so it's giving you some more knowledge about the complicated ways in which these hormones interact," he said.
The findings in chimps (which, as apes, number among our closest relatives) could shed light on the role such close social relationships play in human health too, he said. Such friendships may be just as important during good times as bad -- though more research needs to be done before any conclusions can be drawn.
"This has interest for a lot of people in a medical context as well," Langergraber said.
© 2017 Los Angeles Times under contract with NewsEdge/Acquire Media. All rights reserved.