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Mol Phylogenet Evol. 2018 Sep 25;130:1-8. doi: 10.1016/j.ympev.2018.09.013. [Epub ahead of print]

Improved taxon sampling and multigene phylogeny of unicellular chlamydomonads closely related to the colonial volvocalean lineage Tetrabaenaceae-Goniaceae-Volvocaceae (Volvocales, Chlorophyceae).

Author information

1
Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan; Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, Kanagawa 252-0882, Japan. Electronic address: naktak@ttck.keio.ac.jp.
2
Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan; Department of Environment and Information Studies, Keio University, Fujisawa, Kanagawa 252-0882, Japan.
3
Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, Yamagata 997-0052, Japan; Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, Kanagawa 252-0882, Japan; Department of Environment and Information Studies, Keio University, Fujisawa, Kanagawa 252-0882, Japan.

Abstract

In the green algal order Volvocales (Chlorophyceae), flagellate colonial forms have evolved at least four times. One of these colonial lineages, Tetrabaenaceae-Goniaceae-Volvocaceae (TGV), which belongs to the clade Reinhardtinia, is closely related to several unicellular chlamydomonads in the genera Chlamydomonas and Vitreochlamys. However, the unicellular sister of TGV has not been specified. Here, the largest ever 18S rRNA phylogenetic tree of Reinhardtinia was constructed including several newly isolated chlamydomonads, and a clade (core-Reinhardtinia) including 32 unicellular lineages and three colonial families were recognized. Interrelationships within core-Reinhardtinia were barely resolved in the tree, and therefore combined 18S-atpB-psaA-psaB-psbC-rbcL gene phylogenetic analyses were performed with selected representatives of 29 of the 32 unicellular lineages and three colonial families. The 29 unicellular lineages were clustered into five metaclades and an unassigned lineage; the metaclade that includes Chlamydomonas pila was resolved, with moderate support, as the sister clade to TGV. To examine possible biases from specific gene(s), long-branch taxa, and the heterogeneous base composition, phylogenetic analyses using several smaller data sets were also performed. Light microscopy of C. pila and its relatives indicated that any early steps towards colony evolution appeared after divergence of TGV from the C. pila lineage.

KEYWORDS:

Alga; Chlamydomonas; Colony evolution; Multigene phylogeny; Vitreochlamys; Zoosporangium

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