When Hurricane Maria slammed into Puerto Rico in September 2017, it took 3,000 lives and cut off basic services on some parts of the island for nearly a year. The devastation was not restricted to that island, however. Maria’s 155-mile-per-hour winds also ripped into a 38-acre islet called Cayo Santiago that lies a half mile off the eastern coast of Puerto Rico. This small outpost is home to a colony of some 1,500 rhesus monkeys that has been the subject of hundreds of scientific studies—and the impact of the hurricane on the animals is producing still more.
Amazingly, all of the monkeys survived Maria, though some died soon afterward. But their habitat was ravaged. Trees were stripped of their leaves, making shade a scarce commodity, and the island’s temperature rose by an average of eight degrees Celsius.
The scientific community was immediately concerned about the monkeys’ welfare. Caretakers had to rush to replenish food and repair a destroyed water system. “It was a terrifying time,” recalls neuroscientist Michael Platt of the University of Pennsylvania, who co-leads a multidisciplinary team of researchers that has tracked the biology and behavior of these monkeys for more than a decade.
Once the immediate crisis had passed, however, the scientists realized the disaster had opened a door. “We had a golden opportunity to study the impact of a major natural disaster of the sort that is becoming ever more common with climate change,” Platt says.
The findings of those studies continue to trickle out. A paper published on February 7 in the Proceedings of the National Academy of Sciences USA demonstrates how the calamitous disruption to the lives of macaques on Cayo Santiago may have affected their immune system in ways that accelerate the aging process. The work suggests that storms such as Maria may also lead to premature aging in the people who survive them.
A starting point for this new research on Maria’s impact on the island’s monkeys was actually human studies. Humans who survive trauma of various kinds, such as wars, often show chronic low-grade inflammation, elevated rates of cardiovascular disease and other age-related conditions, says Marina Watowich, an evolutionary biology graduate student at the University of Washington and lead author of the PNAS study. And for some types of traumatic stress, scientists have seen hints of molecular changes in cells that reflect accelerated aging. But no one had been able to document such changes in the context of natural disasters.
These researchers had access to a rare resource: blood samples from the island’s monkeys taken before disaster struck. The animals have blood drawn each year as part of a long-term study of how their genes interact with their social environment. So the team was able to compare blood from 435 rhesus macaques drawn before the hurricane with blood taken from 108 animals one year afterward. “You don’t typically have before and after samples for humans that are going through horrific events,” says behavioral ecologist Daniel Blumstein of the University of California, Los Angeles, who was not involved in the study. The information from these monkeys “does offer an opportunity, and they really mined it.”
Specifically, the researchers looked at the monkeys’ immune cells, which are known to change with age in characteristic ways that can lead to chronic disease. The body’s stress response can also influence the immune system. So stressful experiences are thought to get “under the skin” and lead to chronic conditions by way of the immune system, Watowich says.
The researchers found that monkeys that had experienced the hurricane showed, on average, a pattern of gene expression in their immune cells akin to that of monkeys sampled before the hurricane that were two years older. “The average monkey aged about two years biologically, so it’s about eight years of human life, which is pretty grim,” Platt says.
The storm seemed to etch its greatest effects on so-called heat-shock proteins, a class of proteins produced in response to stress that assist in the proper folding of other proteins. Blood samples taken from monkeys after the hurricane showed decreased expression of genes for these proteins, a pattern that also occurs with aging. Diminished expression of heat-shock protein genes in humans could raise the risk of illnesses, such as Alzheimer’s disease, in which the misfolding of proteins is implicated, the researchers report in their paper.
Storm-stressed monkeys also showed signs of an uptick in the numbers of inflammatory immune cells and a relative decline in cells that suppress inflammation—shifts the researchers also saw in older animals. Increases in inflammation can lead to or exacerbate many chronic diseases of aging, says Noah Snyder-Mackler, an evolutionary biologist at Arizona State University and the study’s senior author.
The work could lead to clues to a mechanism that would explain the effects of natural disasters on disease and longevity. “If we are able to show there are these molecular changes, then it allows us to identify what are some of the potential factors that might impact the onset and progression of age-related diseases,” Snyder-Mackler says.
The molecular results are suggestive but not definitive, says epidemiologist Daniel Belsky of the Columbia Mailman School of Public Health, who was not involved in the study. “There is no gold-standard measure of biological aging,” he says. But taken together, Belsky adds, the data indicate an aging of the animals in response to the hurricane.
That idea has important public health implications, experts say. “Since we expect to see many more climate-change-related disasters in the coming century, quantifying the health costs of exposures will allow us to better estimate the toll these disasters take on our societies and perhaps to proactively intervene,” says evolutionary anthropologist Jenny Tung of Duke University, who was not involved in the research. That toll, Belsky adds, may include a shortened life span and longer periods of disability.
Not every monkey that lived through the storm showed signs of accelerated aging—so Snyder-Mackler and his far-flung colleagues are investigating what might account for some monkeys’ resilience. One hypothesis is strong or numerous social ties. In 2021 a research team that included Platt, Snyder-Mackler and Watowich reported that the macaques reached out and formed more social bonds in the wake of the storm, likely as a coping strategy. Social support is a known protective factor against stress in social species. The researchers now want to know if social ties correlate with immune-system resilience in the macaques.
Another question, Tung says, concerns the potential long-term consequences of the molecular changes the researchers saw. “Will animals exposed to the hurricane actually live shorter than expected lives?” she asks.