Opisthokonta represents a major lineage of eukaryotes and includes fungi and metazoans, as well as other less known unicellular groups. The latter are paraphyletic assemblages that branch in between the former two groups, and thus are important for understanding the origin and early diversification of opisthokonts. The full range of their diversity, however, has not yet been explored from diverse ecological habitats. Freshwater environments are crucial sources for new diversity; they are considered even more heterogeneous than marine ecosystems. This heterogeneity implies more ecological niches where local eukaryotic communities are located. However, knowledge of the unicellular opisthokont diversity is scarce from freshwater environments. Here, we performed an 18S rDNA metabarcoding study in the Middle Paraná River, Argentina, to characterize the molecular diversity of microbial eukaryotes, in particular unicellular members of Opisthokonta. We identified a potential novel clade branching as a sister-group to Fungi. We also detected in our data that more than 60% operational taxonomic units classified as unicellular holozoans (animals and relatives) represent new taxa at the species level. Of the remaining, the majority was assigned to the newly described holozoan species, Syssomonas multiformis. Together, our results show that a large hidden diversity of unicellular members of opisthokonts still remain to be uncovered. We also found that the geographical and ecological distribution of several taxa considered exclusive to marine environments is wider than previously thought.
Bibliographical noteFunding Information:
We thank Mr. Edgardo P. Guglielmetti for technical assistance in the field and Dr. Ramón Massana for his comments on MAST diversity. SN acknowledges the Lerner Gray Memorial Fund of the American Museum of Natural History for aid received. We greatly acknowledge the reviewers' comments, which helped to improve the original manuscript. This work was supported by an American Museum of Natural History's Lerner-Gray Fund for Marine Research grant to SN, a European Research Council Consolidator Grant (ERC-2012-Co-616960), and grants (BFU2014-57779-P and BFU2017-90114-P) from Ministerio de Economía y Competitividad (MINECO), Agencia Estatal de Investigación (AEI), and Fondo Europeo de Desarrollo Regional (FEDER) to IR-T.
© 2018 Arroyo, López-Escardó, Kim, Ruiz-Trillo and Najle.
- Early-branching Holomycota
- Molecular diversity
- Paraná river
- Unicellular Holozoa