Paramecium aureliaRevisited

Journal of Eukaryotic Microbiology - Tập 52 Số 1 - Trang 68-77 - 2005
Annette W. Coleman1
1Division of Biology & Medicine, Brown University, Providence, Rhode Island 02912, USA

Tóm tắt

Abstract.The speciesParamecium aureliasensu latu, containing 15 sexually isolated subspecies (syngens), is the classic example of a sibling species complex in the ciliates. Using DNA sequence comparison, it is now possible to see whether this example parallels other studied sibling species complexes. We sequenced the internal transcribed spacer (ITS) region of the nuclear ribosomal cistron for 13 of the syngens plus two otherParameciumspecies and severalTetrahymenaspp. Using available spirotrich sequences of the internal transcribed spacer 2 (ITS2), we established the RNA transcript folding pattern for ciliates. Ciliates exhibit the two highly conserved helices in their RNA transcript folding pattern in common with other eukaryotes, despite their unusual nuclear behavior and their presumed low copy number of micronuclear ribosomal repeats. Consequently, the set of 111–116 ITS2 nucleotide positions that are relatively conserved in evolution can be derived and used for comparative analysis. Mating behavior (i.e. gamete agglutination and fusion) is the character showing greatest correlation with the degree of ITS2 evolution in theP. aureliacomplex, as also found in other eukaryotes. The degree of change in the ITS2 relatively conserved sequences found among the sibling species ofP. aureliais the same degree as found among the sibling species of theDrosophila melanogaster–mauritania–sechellia–simulans–yakubaspecies complex. The relatively conserved subregion of ITS2, determined from transcript secondary structure, is a tool for identifying the level of the biological species in the absence of knowledge of sexual compatibility in both micro‐ and macro‐eukaryote species complexes.

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Journal of Eukaryotic Microbiology

Tập 52 Số 1

68-77

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