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Journal of Molecular Evolution

, Volume 45, Issue 3, pp 295–300 | Cite as

Algae or Protozoa: Phylogenetic Position of Euglenophytes and Dinoflagellates as Inferred from Mitochondrial Sequences

  • Yuji  Inagaki
  • Yasuko  Hayashi-Ishimaru
  • Megumi  Ehara
  • Ikuo  Igarashi
  • Takeshi  Ohama

Abstract.

The chloroplasts of euglenophytes and dinoflagellates have been suggested to be the vestiges of endosymbiotic algae acquired during the process of evolution. However, the evolutionary positions of these organisms are still inconclusive, and they have been tentatively classified as both algae and protozoa. A representative gene of the mitochondrial genome, cytochrome oxidase subunit I (coxI), was chosen and sequenced to clarify the phylogenetic positions of four dinoflagellates, two euglenophytes and one apicomplexan protist. This is the first report of mitochondrial DNA sequences for dinoflagellates and euglenophytes. Our COXI tree shows clearly that dinoflagellates are closely linked to apicomplexan parasites but not with algae. Euglenophytes and algae appear to be only remotely related, with euglenophytes sharing a possible evolutionary link with kinetoplastids. The COXI tree is in general agreement with the tree based on the nuclear encoded small subunit of ribosomal RNA (SSU rRNA) genes, but conflicts with that based on plastid genes. These results support the interpretation that chloroplasts present in euglenophytes and dinoflagellates were captured from algae through endosymbioses, while their mitochondria were inherited from the host cell. We suggest that dinoflagellates and euglenophytes were originally heterotrophic protists and that their chloroplasts are remnants of endosymbiotic algae.

Key words: Mitochondrial COXI gene — Dinoflagellata — Apicomplexa — Kinetoplastida — Euglenophyta — Endosymbiosis — Genetic code — Malarian circle 

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Copyright information

© Springer-Verlag New York Inc. 1997

Authors and Affiliations

  • Yuji  Inagaki
    • 1
  • Yasuko  Hayashi-Ishimaru
    • 1
  • Megumi  Ehara
    • 2
  • Ikuo  Igarashi
    • 3
  • Takeshi  Ohama
    • 1
  1. 1.Biohistory Research Hall, 1-1 Murasaki-cho, Takatsuki, Osaka 569-11, JapanJP
  2. 2.Department of Biology, Faculty of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560, JapanJP
  3. 3.The Research Center for Protozoan Molecular Immunology, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080, JapanJP

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