Deep relationships of Rhizaria revealed by phylogenomics: a farewell to Haeckel's Radiolaria

Abstract

Rhizaria is one of the six supergroups of eukaryotes, which comprise the majority of amoeboid and skeleton-building protists living in freshwater and marine ecosystems. There is an overall lack of molecular data for the group and therefore the deep phylogeny of rhizarians is unresolved. Molecular data are particularly scarce for the clade of Retaria, which include two prominent groups of microfossils: foraminiferans and radiolarians. To fill this gap, we have produced and sequenced EST libraries for 14 rhizarian species including seven foraminiferans, Gromia and six taxa belonging to traditional Haeckel's Radiolaria: Acantharea, Polycystinea, and Phaeodarea. A matrix was constructed for phylogenetic analysis based on 109 genes and a total of 56 species, of which 22 are rhizarians. Our analyses provide the first multigene evidence for branching of Phaeodarea within Cercozoa, confirming the polyphyly of Haeckel's Radiolaria. It confirms the monophyly of Retaria, a clade grouping Foraminifera with other lineages of Radiolaria. However, contrary to what could be expected from morphological observations, Foraminifera do not form a sister group to radiolarians, but branch within them as sister to either Acantharea or Polycystinea depending on the multigene data set. While the monophyly of Foraminifera and Acantharea is well supported, that of Polycystinea, represented in our data by Spumellaria and Collodaria is questionable. In view of our study, Haeckel's Radiolaria appears as both, a polyphyletic and paraphyletic assemblage of independent groups that should be considered as separate lineages in protist classification.