title: Extreme Diversity of Diplonemid Eukaryotes in the Ocean.
abstract: The world's oceans represent by far the largest biome, with great importance for the global ecosystem [1-4]. The vast majority of ocean biomass and biodiversity is composed of microscopic plankton. Recent results from the Tara Oceans metabarcoding study revealed that a significant part of the plankton in the upper sunlit layer of the ocean is represented by an understudied group of heterotrophic excavate flagellates called diplonemids [5, 6]. We have analyzed the diversity and distribution patterns of diplonemid populations on the extended set of Tara Oceans V9 18S rDNA metabarcodes amplified from 850 size- fractionated plankton communities sampled across 123 globally distributed locations, for the first time also including samples from the mesopelagic zone, which spans the depth from about 200 to 1,000 meters. Diplonemids separate into four major clades, with the vast majority falling into the deep-sea pelagic diplonemid clade. Remarkably, diversity of this clade inferred from metabarcoding data surpasses even that of dinoflagellates, metazoans, and rhizarians, qualifying diplonemids as possibly the most diverse group of marine planktonic eukaryotes. Diplonemids display strong vertical separation between the photic and mesopelagic layers, with the majority of their relative abundance and diversity occurring in deeper waters. Globally, diplonemids display no apparent biogeographic structuring, with a few hyperabundant cosmopolitan operational taxonomic units (OTUs) dominating their communities. Our results suggest that the planktonic diplonemids are among the key heterotrophic players in the largest ecosystem of our biosphere, yet their roles in this ecosystem remain unknown.
authors.affiliation: Institute of Parasitology, Biology Centre, Czech Academy of Sciences, 37005 České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, 37005 České Budějovice, Czech Republic.
authors.forename: Olga
authors.initials: O
authors.lastname: Flegontova
authors.affiliation: Institute of Parasitology, Biology Centre, Czech Academy of Sciences, 37005 České Budějovice, Czech Republic; Faculty of Science, University of Ostrava, 71000 Ostrava, Czech Republic.
authors.forename: Pavel
authors.initials: P
authors.lastname: Flegontov
authors.affiliation: Ecole Normale Supérieure, PSL Research University, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), 75005 Paris, France.
authors.forename: Shruti
authors.initials: S
authors.lastname: Malviya
authors.affiliation: Station Biologique de Roscoff, 29680 Roscoff, France; Sorbonne Universités, 75005 Paris, France.
authors.forename: Stephane
authors.initials: S
authors.lastname: Audic
authors.affiliation: Genoscope, CEA, 91000 Évry, France; CNRS UMR 8030, 91000 Évry, France; Université d'Evry Val d'Essonne, 91000 Évry, France.
authors.forename: Patrick
authors.initials: P
authors.lastname: Wincker
authors.affiliation: Station Biologique de Roscoff, 29680 Roscoff, France; Sorbonne Universités, 75005 Paris, France.
authors.forename: Colomban
authors.initials: C
authors.lastname: de Vargas
authors.affiliation: Ecole Normale Supérieure, PSL Research University, Institut de Biologie de l'Ecole Normale Supérieure (IBENS), 75005 Paris, France.
authors.forename: Chris
authors.initials: C
authors.lastname: Bowler
authors.affiliation: Institute of Parasitology, Biology Centre, Czech Academy of Sciences, 37005 České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, 37005 České Budějovice, Czech Republic; Canadian Institute for Advanced Research, Toronto, ON M5G 1Z8, Canada.
authors.forename: Julius
authors.initials: J
authors.lastname: Lukeš
authors.affiliation: Institute of Parasitology, Biology Centre, Czech Academy of Sciences, 37005 České Budějovice, Czech Republic; Faculty of Science, University of South Bohemia, 37005 České Budějovice, Czech Republic. Electronic address: ogar@paru.cas.cz.
authors.forename: Aleš
authors.initials: A
authors.lastname: Horák
mesh_terms: D059001:Aquatic Organisms / Q000502:physiology; D044822:Biodiversity; D058893:DNA Barcoding, Taxonomic; D017753:Ecosystem; D056898:Euglenozoa / Q000145:classification* / Q000235:genetics; D009792:Oceans and Seas; D010933:Plankton / Q000145:classification* / Q000235:genetics; D016053:RNA, Protozoan / Q000235:genetics; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D017423:Sequence Analysis, RNA
chemical_list: D016053:RNA, Protozoan; D012337:RNA, Ribosomal, 18S
keywords: Tara Oceans; cosmopolitan; diplonemids; diversity; metabarcoding; plankton