Rising temperatures impact the immune system of wild monkeys

The immune systems of wild capuchin monkeys decline in performance when they experience prolonged periods of warmer temperatures, with younger monkeys appearing particularly vulnerable, according to a new study.

Anthropology doctoral student Jordan Lucore from the University of Michigan led the research, which examined how temperature affects the immune systems of white-faced capuchins in Costa Rica. 

Immune performance in wild monkeys

“Rising temperatures due to climate change are predicted to threaten the persistence of wild animals, but there is little evidence that climate change has pushed species beyond their thermal tolerance,” wrote the researchers.

“The immune system is an ideal avenue to assess the effects of climate change because immune performance is sensitive to changes in temperature and immune competency can affect reproductive success.”

The findings, published in Science Advances, revealed that when monkeys endured approximately two weeks of temperatures around 86°F, their generalized immune system performance declined. This system is the body’s first line of defense, activating immediately upon sensing a threat.

Surprising discovery in thermal resilience

The results were unexpected, Lucore explained, because endothermic animals – those that regulate their body temperature, like mammals – are generally thought to be resilient to environmental temperature fluctuations.

“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,” Lucore said. “Eighty-six degrees Fahrenheit is not that hot.”

Capuchin monkeys are considered generalists, thriving in diverse climates and ecologies, which makes the findings even more concerning. “That was another concerning thing about the results: I can’t believe we’re seeing this in capuchins. They are quite resilient,” Lucore noted.

Immune performance of wild monkeys

To study immune system performance, Lucore focused on a biomarker called neopterin, which can be measured in urine rather than blood serum. This non-invasive approach avoided stressing the monkeys and allowed researchers to track individual animals.

Using a method called “clean catch,” the team followed the habituated monkeys until they urinated, collecting the samples with a plastic-lined basket attached to a stick. These samples were then matched to individual monkeys using field observations.

By measuring neopterin levels in the urine and modeling temperature conditions leading up to the sample collection, the researchers established a connection between prolonged high temperatures and declining immune function.

Younger monkeys are more vulnerable

The study found that the immune systems of younger monkeys were particularly impacted by the heat.

“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 when you’re young, you rely on your generalized immune system. Your adaptive immune system has not yet developed.”

The adaptive immune system, which recognizes specific pathogens, takes years to fully develop in young animals. During this early stage of life, a robust generalized immune system is critical for survival, making the observed decline particularly alarming.

Rising temperatures and wild monkeys 

While the study provides strong evidence of temperature’s immediate effects on immune performance, it remains unclear whether these impacts translate to long-term health or reproductive challenges for the monkeys. 

Longer-term studies, potentially spanning multiple generations, are needed to assess the broader consequences.

Lucore emphasized that the findings, though specific to wild capuchins, highlight the broader impacts of climate change on wildlife.

“Climate change is happening. It’s going to have effects on anyone living on Earth in ways that you may not expect, and 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.”

Further research is needed

This study highlights the need for further research into how rising temperatures affect not only capuchins but also other species dependent on stable environmental conditions. 

As climate change accelerates, understanding these vulnerabilities becomes increasingly urgent for conservation efforts.

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