Study: Stress responsiveness in a wild primate predicts survival across an extreme El Niño drought (DOI: 10.1126/sciadv.adq5020)
Faced with relentless drought, capuchin monkeys showcased their remarkable resilience and provided the first data from wild primates to suggest that a stronger stress response promotes survival.
Researchers from the University of Michigan measured hormone levels in capuchins to decode how the stress response helps these monkeys weather environmental challenges. From 2014-2016, a severe El Niño event triggered a drought across Central and South America, leading to unprecedented mortality in a population of white-faced capuchin monkeys in northwestern Costa Rica.
The Lomas Barbudal Monkey Project (directed by co-author Susan Perry of UCLA) has studied this population since 1990. Although the drought was devastating for the long-term research project, it also served as a natural experiment, allowing researchers to compare the stress physiology of the surviving monkeys to those that died.
The findings, which appear in Science Advances, indicate that monkeys who exhibited a robust stress reaction-a notable surge in stress hormones-during past droughts were more likely to endure the severe El Niño conditions than those with milder responses. This result held even after accounting for other factors that influence hormone levels.
"The stress response evolved to help us mobilize the energy we need to get through challenges (think of this as the ability to run from a predator)," said Sofia Carrera, one of the study's first authors and a postdoctoral researcher at Northwestern University. "(But) most research focuses on how stress hormones adversely affect health and longevity."
Jacinta Beehner, U-M professor of psychology and anthropology, and one of the lead authors of the study, says "we are well aware of the 'wear-and-tear' that the stress response puts on all of our systems." She says it's this wear-and-tear that produces the health problems that accumulate in humans, such as heart disease.
However, this is a uniquely human outcome. The stress response in humans does not help us escape modern stressors like mortgages, traffic, and job insecurity, she says.
Wild animals, on the other hand, primarily face challenges where a reactive stress response helps them survive better than a nonreactive one. They can reallocate their energetic resources to escape the predator or survive a drought. This is what the researchers found in the study.
"High levels of stress hormones appear to promote (rather than hinder) survival under challenging conditions when food resources are scarce," Beehner said.
Additional study co-authors include Irene Godoy, Colleen Gault, Ashley Mensing, and Juliane Damm. They and the rest of the Lomas Barbudal Monkey Project team were instrumental in carrying out the study.
