Wild mammals
Outbreaks make macaques wary of contaminated food
Japanese macaques that survived a deadly illness outbreak showed lasting caution around dirty feeding surfaces, according to a recent study.
Reported by Phys.org · · 2 min read
Monkeys that have survived a deadly viral outbreak become far more cautious about eating food that looks dirty, according to a study by researchers at the University of California San Diego published in Royal Society Open Science. The findings suggest that nonhuman primates adapt their pathogen-avoidance behaviors following a disease threat, even without understanding how the infection actually spreads.
The research originated at a primate refuge in southern Texas housing separate troops of Japanese macaques. In 2020, staff detected simian retrovirus Type II among certain troops. The infection caused severe illness and fatalities, spreading primarily through scratches and bites rather than food. Sanctuary workers responded with testing, quarantines, and physical separation, establishing a distinct scenario where three troops experienced the crisis while a fourth group remained entirely unaffected.
Investigators tested 55 monkeys by presenting them with choices between treats on clean wood and treats placed on surfaces coated in monkey waste that had been sealed beneath clear resin. This design preserved visual cues of filth without scent or actual infection risk. Macaques from troops that endured the outbreak accepted food from the dirty-looking surface in only 47 percent of tests, compared to 79 percent among primates from the unexposed group.
Experience shapes avoidance
Remarkably, monkeys in the impacted groups displayed this elevated wariness whether or not they had caught the virus themselves. Because the pathogen traveled through saliva and blood rather than nutrition, researchers noted that merely observing group members suffer and perish altered the primates' tolerance for potential contamination. The team linked these reactions to the behavioral immune system, an evolutionary suite of actions that safeguards animals from illness before internal biological defenses are needed.
In a related experiment examining 54 macaques across seven species, the authors discovered that early development also influenced disease avoidance. Monkeys kept as former pets by humans were significantly more prone to eating from contaminated boards than sanctuary-born animals nurtured by their natural mothers. Researchers suggest that observing maternal cautions during youth provides vital behavioral lessons that persist throughout adult life.
