Diversity-disease relationships in natural microscopic nematode communities.

Host diversity can affect parasite prevalence, a phenomenon widely studied in macroscopic organisms. However, data from microscopic communities are lacking, despite their essential role in ecosystem functioning and the unique experimental opportunities microscopic organisms offer. Here, we study diversity-disease effects in wild nematode communities by profiting from the molecular tools available in the well-studied model nematode Caenorhabditis elegans. Nanopore sequencing was used to characterize nematode community diversity and composition, whereas parasites were identified using nine distinct experimental assays based on fluorescent staining or fluorescent reporter strains. Our results indicate that biotic stress is abundant in wild nematode communities. Moreover, in two assays, diversity-disease relations were observed: microsporidia and immune system activation were more often detected in relatively species-poor communities. Other assays, targeting different parasites, were without diversity-disease relations. Together, this study provides the first demonstration of diversity-disease effects in microbial communities and establishes the use of nematode communities as model systems to study disease-diversity relationships.