High temperatures are associated with decreased immune system performance in a wild primate

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. 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. We investigate the effect of rising temperatures on a biomarker of non-specific immune performance in a wild population of capuchin monkeys and provide compelling evidence that immune performance is associated with ambient temperature. Critically, we found that immune performance in young individuals is more sensitive to high temperatures compared to other age groups. Coupled with evidence of rising temperatures in the region, our results offer insight into how climate change will affect the immune system of wild mammals.

Methods
Between Sep 2021 and Aug 2023 we collected 676 urine samples from three habituated groups of wild C. imitator associated with the Capuchinos de Taboga research project in the Taboga Forest Reserve. We measured the neopterin concentration of all samples using a commercially available competitive exclusion neopterin ELISA (Neopterin ELISA, Ref. RE59321, IBL International GMBH, Hamburg, Germany) in the Capuchinos de Taboga field laboratory. The kit was developed to detect neopterin concentration in human serum, plasma, and urine, but has been validated for use in the wild C. imitator population associated with the Capuchinos de Taboga research project. We removed three samples that were 4 SD above the mean before conducting our analysis. We also removed three samples associated with the oldest individual in our population (34 years of age at the beginning of the study) to standardize the age spread across social groups.