title: Phylogenetic Position and Molecular Chronology of a Colonial Green Flagellate, Stephanosphaera pluvialis (Volvocales, Chlorophyceae), among Unicellular Algae.
abstract: The genus Balticola comprises a group of unicellular green flagellate algae and is composed of four species formerly classified in the genus Haematococcus. Balticola is closely related to a colonial green flagellate, Stephanosphaera pluvialis. Although the phylogeny among these genera was previously investigated based on two nuclear gene sequences, the phylogenetic sister of S. pluvialis has yet to be determined. In the present study, the species diversity of Balticola and Stephanosphaera was investigated using 18S rRNA gene sequences, and phylogenetic analyses of combined nuclear and chloroplast gene sequences were performed to understand the evolutionary origin of coloniality in Stephanosphaera. The divergence times of four colonial volvocalean flagellates from their respective unicellular sisters were also estimated. Six Balticola genotypes and a single Stephanosphaera genotype were recognized, and one Balticola genotype was resolved as the sister of S. pluvialis, showing that Balticola is a nonmonophyletic genus. The divergence time of Stephanosphaera from its nearest Balticola relative was estimated to be 4-63 million years ago, and these genera represent the most recently diverged pair of unicellular and colonial flagellates among the Volvocales.
authors.affiliation: Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, 252-0882, Japan.|Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, 997-0052, Japan.
authors.forename: Hidehito
authors.initials: H
authors.lastname: Munakata
authors.affiliation: Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, 252-0882, Japan.|Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, 997-0052, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakada
authors.affiliation: Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, 252-0882, Japan.|Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, 997-0052, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Nakahigashi
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 113-0033, Japan.
authors.forename: Hisayoshi
authors.initials: H
authors.lastname: Nozaki
authors.affiliation: Systems Biology Program, Graduate School of Media and Governance, Keio University, Fujisawa, 252-0882, Japan.|Institute for Advanced Biosciences, Keio University, Kakuganji, Tsuruoka, 997-0052, Japan.
authors.forename: Masaru
authors.initials: M
authors.lastname: Tomita
mesh_terms: D018742:DNA, Chloroplast / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D019143:Evolution, Molecular; D014644:Genetic Variation; D005838:Genotype; D010802:Phylogeny; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics; D016823:Volvocida / Q000145:classification* / Q000235:genetics*
chemical_list: D018742:DNA, Chloroplast; D004275:DNA, Ribosomal; D012273:Ribulose-Bisphosphate Carboxylase
keywords: Balticola; coloniality; divergence time; evolution; molecular phylogeny