Monkeys also avoid germs after viral outbreaks
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Macaques who survived the spread of a deadly disease were more wary of potentially contaminated food. The post Monkeys also avoid germs after viral outbreaks appeared first on Popular Science .
When a new disease emerges, things can get a little weird. We start to clean groceries with antibacterial wipes, the sound of a sneeze can trigger our fight-or-flight response, and we generally become more cautious. Humans may not be the only primate species that change their behavior in the face of disease.
According to a study published today in the journal Royal Society Open Science, Japanese macaques ( Macaca fuscata ) that lived through a deadly outbreak in 2020 became noticeably more cautious about food that appeared contaminated, even though this disease was not spread by food or feces. This indicates that purposefully shifting behavior to avoid a pathogen can be shaped by our appearance and that disgust may have deep evolutionary roots. It also sheds light on the behavioral immune system—a collection of behaviors that help animals avoid an infection before the biological immune systems respond.
“We can show now, in non-human primates, that this is the same for them,” Federico Rossano , a study co-author and cognitive psychologist at the University of California San Diego, said in a statement . “Even with no knowledge of how disease is transmitted, being exposed to others getting sick and dying changes the likelihood of engaging in behaviors that potentially could lead to some form of sickness.”
In 2020, the staff at a primate sanctuary in southern Texas confirmed the presence of simian retrovirus Type II. This disease can cause AIDS-like immunodeficiency and is primarily transmitted through bites and scratches. It caused severe illness and death in some of the monkeys. The sanctuary staff separated the groups and implemented testing and quarantine measures in response to the outbreak. Since the groups live in separate enclosures, scientists then had the chance to compare animals with similar backgrounds that had experienced very different social and disease environments.
In total, three groups of monkeys experienced the outbreak while one had not. The team tested
55 macaques to see how they responded to a choice between food that was put on a clean wooden surface and food placed on a surface covered with real macaque feces. The food with the feces was sealed under a layer of clear epoxy, so that the monkeys could see the food and poop without risking infection.
In the group that had been exposed to the outbreak, some of the individuals had been infected while others had lived alongside sick monkeys without getting sick. This allowed the researchers to question if experiencing an outbreak without getting infected could change the macaque’s behavior. To test that further, the clean surface was replaced with a brightly colored kitchen sponge in some of the scenarios to see if the animals were just avoiding unfamiliar objects.
Previous studies found that macaques aren’t necessarily deterred by contamination—as long as the payoff is tempting. When presented with a favorite treat (such as a peanut) wild Japanese macaques would still eat food from a surface covered in feces, but will avoid it for food like grains of wheat.
The team found that macaques from groups that went through the outbreak were far less likely to eat the food from the contaminated surface. They ate from the fake contaminated surface in only 47 percent of trials. The monkeys that did not experience the outbreak ate from the potentially contaminated surface in 79 percent of trials.
The monkeys from outbreak-exposed groups also behaved similarly whether or not they themselves had been infected. According to the team, this suggests the behavioral change was associated with their experiencing living through the outbreak, instead of actually getting sick
“Groups have histories, and those histories show up in behavior,” added study co-author and UC San Diego cognitive psychologist Stephan Kaufhold . “Living through the disease outbreak appears to have made those monkey groups more cautious around food that looks contaminated.”
The virus was spread through blood or saliva from bites and scratches, and not through contaminated food. Interestingly, the macaques who saw their fellow primates get sick, were more reluctant to eat food placed on a surface that visually suggested contamination in some of the tests.
In addition to shedding light on how illness affects primate behavior, it also offers insight into the evolution of disgust. The team did not measure disgust directly, but found that monkey’s avoidance of potential sources of infection can change with their experience, similar to what humans do.
Human disgust is believed to play an important role in protecting us from pathogens. We recoil from the smell and sight of poop, spoiled food, and other potential sources of infection. Our sensitivity to those cues can also change depending on context.
Since primates are capable of social learning, the team believes that heightened pathogen avoidance could be learned from other members in the group and persist over time. Future studies could see if newly introduced animals adopt the behavior of a group that has already experienced an outbreak.
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