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, 6 (8), e23526

Radiolaria Divided Into Polycystina and Spasmaria in Combined 18S and 28S rDNA Phylogeny

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Radiolaria Divided Into Polycystina and Spasmaria in Combined 18S and 28S rDNA Phylogeny

Anders K Krabberød et al. PLoS One.

Abstract

Radiolarians are marine planktonic protists that belong to the eukaryote supergroup Rhizaria together with Foraminifera and Cercozoa. Radiolaria has traditionally been divided into four main groups based on morphological characters; i.e. Polycystina, Acantharia, Nassellaria and Phaeodaria. But recent 18S rDNA phylogenies have shown that Phaeodaria belongs within Cerocozoa, and that the previously heliozoan group Taxopodida should be included in Radiolaria. 18S rDNA phylogenies have not yet resolved the sister relationship between the main Radiolaria groups, but nevertheless suggests that Spumellaria, and thereby also Polycystina, are polyphyletic. Very few sequences other than 18S rDNA have so far been generated from radiolarian cells, mostly due to the fact that Radiolaria has been impossible to cultivate and single cell PCR has been hampered by low success rate. Here we have therefore investigated the mutual evolutionary relationship of the main radiolarian groups by using the novel approach of combining single cell whole genome amplification with targeted PCR amplification of the 18S and 28S rDNA genes. Combined 18S and 28S phylogeny of sequences obtained from single cells shows that Radiolaria is divided into two main lineages: Polycystina (Spumellaria+Nassellaria) and Spasmaria (Acantharia+Taxopodida). Further we show with high support that Foraminifera groups within Radiolaria supporting the Retaria hypothesis.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Light micrographs of the specimens studied.
Pictures are taken directly from seawater samples in petri dishes under a Zeiss RA Compound microscope prior to washing. All scale bars are 50 µm. A) Actinomma boreale #43, B) A. boreale #47, C) A. boreale #72, D) A. boreale #79, E) Cladococcus viminalis #83, F) C. viminalis #302, G) Hexaconthium gigantheum # 9, H) H. gigantheum #12, I) H. gigantheum #293, J) H. pachydermum #71, K) H. pachydermum #86, L) H. pachydermum #294, M) Phorticium pylonium #245, N) Streblacantha circumtexta #299, O) Ceratospyris hyperborea #134, P) Cladoscenium tricolpium #49, Q) Eucyrtidium calvertense #129, R) Lithomelissa setosa #2, S) L. setosa #15, T) Acanthonia nordgaardi #16, U) A. nordgaardi #32, V) Challengeron diodon #18, W) Medusetta archifera #24, X) Protocystis tridens #143, Y) Sticholonche zancela #313.
Figure 2
Figure 2. Maximum likelihood (ML) phylogeny of Radiolaria inferred from an 18S rDNA alignment consisting of 158 taxa and 1438 characters.
Values at nodes represent bootstrap support values from ML analysis and Bayesian posterior probabilities (pp) (ML/pp). Filled circle indicate maximum support in both analyses. Only values above 70% and 0.85 pp are shown (except at a few backbone nodes) and only at selected nodes due to space constraints. Hyphen indicates values below the threshold. Values in parentheses indicate support values when the analyses were run without Foraminifera (ML/pp) and are only shown for the main groups.
Figure 3
Figure 3. Maximum likelihood (ML) phylogeny of Radiolaria inferred from an 18S + 28S rDNA alignment consisting of A) 24 taxa and 4163 characters, and B) 27 taxa and 4163 characters (including Foraminifera).
Values at nodes represent bootstrap support values from ML analysis and Bayesian posterior probabilities (pp) (ML/pp). Filled circle indicate maximum support in both analyses. Numbers in parenthesis represent the peak support values after removing fast evolving sites for selected nodes (cf. Table S3 and S4).

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