Stress helps capuchin monkeys survive in extreme weather 

White-faced capuchin monkeys in Costa Rica displayed a surprising ability to withstand extreme drought conditions, according to a new study led by University of California, Los Angeles (UCLA) researchers. 

The research highlights how a robust stress response during mild droughts prepared these capuchin monkeys to endure catastrophic events like the severe El Niño drought from 2014 to 2016. 

The study offers fresh insights into the adaptive role of stress responses in wild animals, with implications for both evolutionary biology and conservation.

Stress response helps monkeys survive

Stress is often viewed as harmful, associated with “wear-and-tear” on the body. However, this study aimed to explore how the physiological stress response might serve an adaptive function. 

“We wanted to understand how the stress response adaptively helps these individuals survive greater challenges,” explained Susan Perry, a UCLA evolutionary anthropologist and co-author of the study.

Perry and her team leveraged the devastating El Niño drought as a natural experiment to investigate how hormonal stress responses correlated with survival outcomes in white-faced capuchin monkeys.

El Niño’s impact on monkeys

The El Niño drought, the most severe in recent history, significantly altered the lives of the monkeys at the Lomas Barbudal Capuchin Monkey Project in Guanacaste, Costa Rica. For over 35 years, Perry and her team have documented the lives and social behaviors of these monkeys. 

However, the extreme drought pushed the population to its limits, with widespread food shortages leading to visible weight loss, abandonment of infants, and drastically reduced caretaking behaviors. Mortality rates soared, especially among infants and older females.

According to Perry, this was the only time in their longitudinal study that these monkeys, who are usually behaviorally flexible, did not manage to adapt to an environmental stressor by simply changing how they behaved.

Indicators of stress in monkeys

The researchers analyzed fecal samples collected between 2008 and 2013 from 28 female monkeys – 14 who survived the drought and 14 who did not. These samples contained glucocorticoids, hormones that regulate metabolism, immune response, and inflammation.

The findings revealed that monkeys exhibiting a more pronounced rise in glucocorticoid levels during mild droughts were significantly more likely to survive the severe El Niño drought. This result held true even after accounting for variables like pregnancy and time of day.

The study provides a clearer understanding of how an adaptive stress response looks in this species. These findings suggest that a steeper hormonal response to milder stressors might prepare individuals to cope with more extreme challenges in the future.

Long-term studies in a changing climate

The research underscores the importance of longitudinal studies in understanding how animals cope with increasingly extreme weather events caused by climate change. 

Perry’s team believes that such studies can reveal which species possess the physiological flexibility to adapt to rapidly changing environments and which are more vulnerable.

For instance, the white-faced capuchins’ inability to adapt behaviorally during the drought marked a stark departure from their usual flexibility, raising questions about the limits of such adaptability in other species. 

Long-term data like this can help conservationists identify species or populations at risk and guide interventions.

According to the experts, a population of highly endangered animals that cannot quickly adapt to change might need to be moved to a place that now has climatic conditions that match the environment in which that population evolved.

Evolutionary biology and conservation

The study not only sheds light on the origins and maintenance of individual differences in stress responses but also has broader implications for evolutionary biology. Understanding how certain physiological traits enhance survival can provide clues about the pressures that shape species over time.

As climate change continues to intensify, studies like this are essential for identifying species’ resilience thresholds and informing conservation strategies. 

For white-faced capuchins, their robust stress response during mild droughts was a life-saving adaptation during an extreme environmental crisis – offering a glimmer of hope for the survival of species in an increasingly volatile world.

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