The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes

doi:10.1073/pnas.0308602101

The twilight of Heliozoa and rise of Rhizaria, an emerging supergroup of amoeboid eukaryotes

^†A. N. Belozersky Institute of Physico-Chemical Biology, Department of Evolutionary Biochemistry, Moscow State University, Moscow 119992, Russia; ^‡Department of Zoology and Animal Biology, University of Geneva, 1211 Geneva 4, Switzerland; and ^§Institute for Biology of Inland Waters, Russian Academy of Sciences, Yaroslavskaya oblast, Borok 152742, Russia

Edited by W. Ford Doolittle, Dalhousie University, Halifax, Nova Scotia, Canada, and approved April 9, 2004 (received for review December 23, 2003)

Abstract

Recent molecular phylogenetic studies revealed the extraordinary diversity of single-celled eukaryotes. However, the proper assessment of this diversity and accurate reconstruction of the eukaryote phylogeny are still impeded by the lack of molecular data for some major groups of easily identifiable and cultivable protists. Among them, amoeboid eukaryotes have been notably absent from molecular phylogenies, despite their diversity, complexity, and abundance. To partly fill this phylogenetic gap, we present here combined small-subunit ribosomal RNA and actin sequence data for the three main groups of “Heliozoa” (Actinophryida, Centrohelida, and Desmothoracida), the heliozoan-like Sticholonche, and the radiolarian group Polycystinea. Phylogenetic analyses of our sequences demonstrate the polyphyly of heliozoans, which branch either as an independent eukaryotic lineage (Centrohelida), within stramenopiles (Actinophryida), or among cercozoans (Desmothoracida), in broad agreement with previous ultrastructure-based studies. Our data also provide solid evidence for the existence of the Rhizaria, an emerging supergroup of mainly amoeboid eukaryotes that includes desmothoracid heliozoans, all radiolarians, Sticholonche, and foraminiferans, as well as various filose and reticulose amoebae and some flagellates.

Footnotes

↵ ¶ To whom correspondence should be addressed. E-mail: jan.pawlowski{at}zoo.unige.ch.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: BV, bootstrap support value; ML, maximum likelihood; PP, posterior probability; SSU rRNA, small-subunit ribosomal RNA.
Data deposition: The sequences reported in this paper have been deposited in the GenBank/EMBL database (accession nos. AY268041–AY26843, AY268045, AY283744–AY283746, AY283754–AY283762, AY305008–AY305013, and AY507123–AY507125).