Temperature and Rainfall Associate With Patterns of Parasitism in Free-Ranging Capuchin Monkeys (Cebus imitator).

Ecological variables such as climate and habitat composition can impact the infection patterns of gastrointestinal parasites in animal host populations by affecting host behavior and parasite survivability and distribution in the external environment. Data from wild primate populations provide insights into these processes. To contribute new insights from a well-characterized population, we collected 200 fecal samples from five groups of Costa Rican capuchin monkeys from August 2020 to August 2021 and screened them for gastrointestinal parasites. We estimated annual home range sizes for the groups and used satellite imagery to measure forest productivity (via Normalized Difference Vegetation Index) and forest cover within their home ranges. We also measured total monthly rainfall and average monthly temperature at the field site to explore the effects of local climate on parasitism. We used Bayesian regression models to examine the effects of these ecological variables on parasite richness, fecal parasite density, and parasite presence. We found that rainfall, and to a lesser extent, temperature, affected the presence and fecal density of certain parasitic taxa. The presence of the soil-transmitted helminth Strongyloides decreased in both hotter and rainier months, and hosts shed fewer Strongyloides eggs during hotter months. Infections with indirectly transmitted parasites (e.g., Prosthenorchis sp., Hymenolepis sp.) were more common during drier months. This corresponds with times when fruit availability is lower and invertebrate consumption is higher at this site. These findings highlight the relationship between climate and patterns of parasitic infection in hosts, likely reflecting changes in host diet, behavior, and parasite abundance.