Molecular phylogeny and species delimitation within the ciliate genus Spirostomum (Ciliophora, Postciliodesmatophora, Heterotrichea), using the internal transcribed spacer region.
Morphological and molecular delimitation of Spirostomum species is currently under debate. We addressed species boundaries within the genus Spirostomum, using the ITS1-5.8S-ITS2 region and the secondary structure of the ITS2 molecule, and 18S and 28S (D1D2) sequences additionally. The Spirostomum ITS region is among the shortest within the ciliates hitherto studied. The Spirostomum ITS2 molecule matches the "ring model", but exhibits only two helices radiating from a common loop. According to comparative analyses, they very likely correspond to helices II and III of other eukaryotes. Our phylogenetic analyses of the ITS region revealed a complex genealogical structure within the genus Spirostomum. However, boundaries among Spirostomum species could not be unambiguously determined either by phylogenetic trees, networks or sequence divergence cutoffs, because ITS2 sequences transcended species boundaries of the following morphospecies: S. ambiguum, S. minus, S. subtilis and S. teres. According to molecular diversity analysis, this is very likely caused by polymorphism in S. minus and S. teres, and by the lack of variability in S. ambiguum and S. subtilis. No compensatory base changes (CBCs) were detected in helices of the ITS2 molecule between different Spirostomum species, documenting that CBC analysis per se is not able to effectively discriminate Spirostomum species.
Department of Biological Sciences, University of Ulsan, Ulsan 44610, South Korea.
Shahed Uddin Ahmed
SU
Shazib
Department of Zoology, Comenius University in Bratislava, 84215 Bratislava, Slovakia. Electronic address: vdacny@fns.uniba.sk.
Peter
P
Vďačný
Department of Biological Sciences, University of Ulsan, Ulsan 44610, South Korea.
Ji Hye
JH
Kim
Department of Biological Sciences, University of Ulsan, Ulsan 44610, South Korea.
Seok Won
SW
Jang
Department of Biological Sciences, University of Ulsan, Ulsan 44610, South Korea. Electronic address: mkshin@ulsan.ac.kr.
Mann Kyoon
MK
Shin
D000818:Animals; D001483:Base Sequence; D016798:Ciliophora / Q000145:classification* / Q000235:genetics; D004247:DNA / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014644:Genetic Variation; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D021903:DNA, Ribosomal Spacer; D004247:DNA
CBCs; ITS1-5.8S-ITS2 region; ITS2 secondary structure; Spirostomum