The diversity of biological communities is often described without considering parasites. Instead, parasites are often studied alongside bacterial and viral pathogens using the tools of disease ecology. Parasites become obvious in situations such as zoonotic spillover and outbreaks among host populations. In contrast, the loss of parasite biodiversity can go unnoticed. This project uses DNA metabarcoding as a method to survey the parasite communities of fish in the Colorado River in Grand Canyon, focusing on protists, or unicellular eukaryotes. Parasitic protists are often neglected because they are difficult to locate and identify, making them good subjects for a molecular approach. Parasites have pervasive effects on behavior and mortality in host populations, and they create unique trophic linkages between intermediate and definitive hosts. In a heavily monitored and managed ecosystem like Grand Canyon, understanding parasite communities deepens our understanding of effective management and emerging threats.
DNA was extracted from samples collected between 2022 and 2024 throughout the length of the canyon, including filtered water samples, as well as fecal samples from over 250 Catostomus latipinnis (flannelmouth sucker), 20 Oncorhynchus mykiss (rainbow trout), and 77 federally threatened Gila cypha (humpback chub). Eukaryotic 18s sequences were amplified and Illumina NGS sequenced to generate taxon lists which were then filtered to parasitic taxa. In addition, data on fish size and health was collected in the field.
In our updated multi-year results we detected over 200 parasites of fish and invertebrates, originating in samples sourced from both fish and water. NMDS ordination further revealed distinct community fingerprints for each fish species and sampling year. Water from tributary streams was especially diverse, supporting current ecological theories of dam-driven environmental homogenization and degradation in the mainstem. Key parasites of fishes we detect include the introduced Asian fish tapeworm Bothriocephalus acheilognathi, as well as myxozoan DNA present in over half the samples. We observe distinct instances of temporal patterning in parasite occurrence, such as a four-fold spike in microsporidian DNA detections in 2023. These results provide a baseline for monitoring parasite biodiversity and prevalence, and inform the rapidly evolving management situation in Grand Canyon.