Researchers in Costa Rica utilized environmental data and fecal samples from the six years leading up to the significant El Niño drought to explore the link between endocrine stress responses and the survival of white-faced capuchin monkeys. The findings revealed that monkeys exhibiting a sharp increase in stress hormones during milder droughts had a higher likelihood of surviving the intense El Niño drought. As global weather patterns become more extreme, longitudinal research on how wild animals manage temperature, rainfall, and food supply shifts can reveal which species can adapt swiftly.
A recent study led by UCLA reveals that white-faced capuchin monkeys in Costa Rica who had stronger physiological responses to mild droughts were better equipped to survive severe drought conditions.
Typically, studies on wild animals and humans focus on the negative impacts of stress responses—what is often termed “wear and tear.” However, this new study, published in Science Advances, aims to investigate the beneficial aspects of stress responses in wild primates, positing that a more vigorous stress response could aid survival during severe environmental events.
“Our aim was to understand how stress responses can help individuals adapt and endure greater challenges,” explained Susan Perry, a UCLA evolutionary anthropologist, field primatologist, and co-author of the study.
Because it wasn’t feasible to experiment with identical stressors on every monkey, researchers capitalized on a natural experiment—the intense El Niño drought—to examine the correlation between hormonal responses to this extreme climate stressor and the survival of white-faced capuchins at the Lomas Barbudal Capuchin Monkey Project in Guanacaste, Costa Rica.
Perry and her research team have been observing the behaviors and survival strategies of monkeys in Guanacaste for 35 years. For this study, her team collaborated with researchers Jacinta Beehner and Sofia Carrera from the University of Michigan, along with current and former graduate students and research assistants like Irene Godoy, Ashley Mensing, Juliane Damm, and Colleen Gault.
A drought leads to new insights
The El Niño drought that affected Central and South America from 2014 to 2016 was the worst in recent times, resulting in many monkey deaths. Although this was tragic for both the monkeys and the researchers, it allowed Perry’s team to use the collected environmental data and previous samples from the six years prior to investigate the endocrine stress response related to survival in the white-faced capuchins.
During the drought, monkeys began to lose weight, showing their vertebrae and ribs; some mothers even abandoned their infants to search for food. Typically, monkeys take on caregiving roles for infants in their absence, but even these behaviors ceased. Mortality rates surged, particularly among infants and older females. This period marked the only instance in Perry’s extensive research where these behaviorally adaptable monkeys failed to adjust to an environmental challenge through changes in behavior, such as adjusting their diet.
The researchers analyzed glucocorticoid levels in fecal samples from 14 surviving female monkeys and 14 that died, using samples collected in the six years leading up to the El Niño drought (2008-2013). Glucocorticoids are hormones that play a key role in regulating metabolism, inflammation, and the immune response.
What fecal glucocorticoid levels revealed about survival
The analysis found that monkeys with a more pronounced increase in stress hormones during mild droughts had a greater chance of surviving the severe El Niño drought than those exhibiting a lesser stress response. The results accounted for various factors that could influence hormone levels, including pregnancy and the time of day.
With a clearer understanding of what constitutes an adaptive stress response for this species, Perry’s team can explore the origins and persistence of individual differences in endocrine responses and their impacts on survival.
This research underscores the importance of long-term studies in understanding climate change. As global weather patterns escalate, longitudinal studies on how wild animals adjust to shifts in temperature, rainfall, and food supplies can indicate which species can swiftly adapt through learning or physiological changes, and which species might struggle to cope with significant environmental shifts during their lifetimes. This information is critical for conservation efforts. For instance, highly endangered species that cannot adapt quickly to changes may need to be relocated to areas with climates that match those in which the species initially thrived.
