A recent study which might have implications for how mammals respond to climate change has shown that for one Costa Rican monkey, higher temperatures resulted in weaker immune systems.

According to the University of Michigan study of capuchin monkeys, published in Science Advances, when the monkeys experience about two weeks of warmer temperatures, the performance of their generalised immune system declines.

Warmer temperatures were days when the average temperature was 30°C (86°F.)

“86 degrees Fahrenheit is not that hot,” said the study’s author Jordan Lucore, a University of Michigan anthropology doctoral student.

Capuchin monkeys are thought of as a “successful generalist” species, according to Lucore. This is because they live in a variety of environments across diverse climates.

“That was another concerning thing about the results: I can’t believe we’re seeing this in capuchins. They are quite resilient.”

Monkeys are endothermic meaning they can regulate their own body temperature, like other mammals such as us humans.

The results surprised Lucore and the team, as it was expected that wild mammals should be able to protect themselves in the heat and maintain a constant body temperature.

“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.”

To conduct their research, the team examined a biomarker called neopterin. Neopterin levels indicate cell immunity and immune system activation.

Neopterin can be measured from a urine sample, so to collect samples researchers used a ‘clean catch’ method which involves following the monkeys around and catching their urine in baskets attached to sticks.

After analysing the urine samples, the team also found that the decline in immune system performance was more severe in younger monkeys.

“This is especially important for potential health and fitness outcomes, because when you’re young, you rely on your generalized immune system,” says Lucore.

“Your adaptive immune system has not yet developed.”

The adaptive immune system refers to the immune system’s ability to remember certain pathogens and microorganisms which allows for a more efficient response to future exposures. It can take a young animal several years to develop an adaptive immune system.

More studies are needed to look into whether this decreased immune performance in young wild monkeys will have long-term health impacts.

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

“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.”

To save our mammals, we really need to know them.