SE Valley Times

In 2017, Hurricane Maria struck Puerto Rico, resulting in over 3,000 fatalities and causing more than $100 billion in damages. The hurricane also devastated 63% of the vegetation on Cayo Santiago, an island known as Monkey Island, home to approximately 1,800 rhesus macaque monkeys. Despite the destruction, only 2.75% of the macaque population perished immediately after the storm.

A recent study led by scientists from Exeter University and the University of Pennsylvania, in collaboration with Arizona State University and New York University, has revealed that the storm's damage altered the evolutionary benefits of social tolerance among these monkeys. The research indicates that increased tolerance and cooperation among macaques have provided a survival advantage in sharing limited resources like shade.

The study was funded by the National Institutes of Health, the European Research Council, the National Science Foundation, and the Royal Society. It has been featured on the cover of Science journal.

Cayo Santiago has hosted an isolated population of rhesus macaques since 1938, serving as a natural laboratory with extensive data collection. Study co-author Noah Snyder-Mackler described it as “a Goldilocks research system — the perfect mix of the wild and the lab.”

A 2022 study on Cayo Santiago's monkeys suggested that survivors of weather-related disasters might experience accelerated aging. "What we are trying to do right now is look at what makes some of these individuals more resilient to the effects of the hurricane," Snyder-Mackler said.

Five years post-hurricane, tree cover remains significantly reduced on Cayo Santiago. This scarcity makes shade a critical resource for survival in this hot region.

"In response to the drastic changes caused by the hurricane, macaques persistently increased tolerance and decreased aggression towards each other," said lead author Camille Testard from the University of Pennsylvania and now a junior fellow at Harvard. "This enabled more macaques to access scarce shade."

Testard explained that examining ten years of data revealed a shift in survival patterns: before Hurricane Maria, social tolerance had no impact on mortality risk; afterward, more tolerant macaques were 42% less likely to die than their less tolerant counterparts.

Senior author Lauren Brent from Exeter University noted that "the hurricane changed the rules of the game" for these typically aggressive and competitive animals. Brent added that such studies show how social relationships can help group-living animals cope with environmental disturbances.

Ultimately, researchers hope insights from this study could inform strategies for human resilience against similar catastrophic events. “Given the strong similarity between these monkeys and us,” Snyder-Mackler said, “we know that a lot of...the things that [they] might do to be more resilient...might provide ways for us to intervene and help buffer against...traumatic events.”