Metabarcoding analysis of 18S eukaryotic diversity in the Paraná River, Argentina (V4 region)

Understanding the real eukaryotic diversity is essential to address ecological and evolutionary questions. Among eukaryotes, Opisthokonta includes Fungi and Metazoa, as well as other less known unicellular lineages that are key to understand the evolution of both fungi and animals. Thus, it is necessary to study the diversity of opisthokonts in different environments. Freshwater habitats are a perfect option, because they remain undersampled compared to marine environments, and their heterogeneity might be a powerful force for diversification and evolution. Here, we performed an 18S rDNA metabarcoding study in the Paraná River, Argentina, to better understand the molecular diversity within Opisthokonta. We recovered a considerable amount of diversity in early-diverging fungal groups and we identified a potential novel clade branching as sister-group to the rest of Fungi. Moreover, we also found substantial molecular diversity in Holozoa (animals and their closest relatives), being the plurimorfean Syssomonas multiformis, so far only described in a Vietnamese lake, the most abundant unicellular holozoan taxon. Finally, we detected several taxa previously thought to be exclusively marine. Overall, our results show that there is a great proportion of unknown diversity within the unicellular closest relatives to animals and fungi, and that those have a wide global distribution.