Warming temperatures impact the immune performance of wild monkeys

Rising temperatures from climate change threaten wildlife, but evidence of species exceeding their thermal limits is limited. The immune system offers a valuable way to assess climate change impacts, as immune function is sensitive to temperature changes and can influence reproductive success.

A University of Michigan study on wild capuchin monkeys in Costa Rica found that rising temperatures negatively impact immune performance, with younger monkeys particularly vulnerable. After just two weeks of exposure to temperatures around 86°F, the monkeys’ immune systems showed a decline in nonspecific immune performance, highlighting the potential health risks of climate change.

This was surprising, as researchers typically expect endothermic animals, like mammals, to regulate their body temperature and protect themselves from temperature fluctuations.

U-M anthropology doctoral student Jordan Lucore said, “We think this has implications for understanding the effects of climate change because we’re seeing this unlikely relationship between the immune system and temperature in this particular study species, and we’re seeing it at much lower temperatures than expected.”

The study, part of the Capuchinos de Taboga Research Project, examined wild white-faced capuchins in Costa Rica’s Taboga forest reserve. Co-directed by experts from the University of Michigan and Emory University, the project focuses on capuchin cognition, endocrinology, and behavior.

Despite Capuchins’ reputation as a resilient generalist, the study found an unexpected immune system decline.

To reduce invasiveness, the team measured the biomarker neopterin in urine instead of using blood samples. They used a “clean catch” method to collect urine from the capuchins, ensuring it wasn’t contaminated by falling on the ground. To avoid stressing the monkeys, they carefully followed the habituated animals until they urinated, then collected the samples using a plastic-wrapped basket on a stick.

Each monkey was individually identified to track urine samples. Researchers measured neopterin levels in the urine and analyzed temperature data from the preceding weeks.

The study found that immune performance declined after two weeks of high temperatures, with younger monkeys showing the most significant immune impact.

“We discovered that young individuals’ immune systems may be particularly affected by temperature compared to the rest of the age groups,” Lucore said. “This is especially important for potential health and fitness outcomes because you rely on your generalized immune system when you’re young. Your adaptive immune system has not yet developed.”

The adaptive immune system is the component of the immune system that recognizes specific pathogens. It takes young animals up to several years to develop this system.

Lucore said the researchers don’t know yet whether this has long-term impacts on wild animal health. Longer-term studies must examine multiple generations to conclude whether the monkeys’ decreased immune performance results in poorer health or reproductive outcomes. Lucore also said the results may be difficult to apply to humans, but they can tell us about how climate change impacts wild animal populations.

“Climate change is happening. It will affect anyone living on Earth in ways that you may not expect, especially on these fundamental systems that we need to survive,” Lucore said. “The fact that a graduate student like me can go out there and collect rather short-term data and find strong evidence that temperatures are affecting the physiology of wild animals—I think that’s a pretty important thing to keep in mind.”

Journal Reference:

1. Jordan Lucore, Jacinta Beehner et al. High temperatures are associated with decreased immune system performance in a wild primate. Science Advances. DOI: 10.1126/sciadv.adq6629