Phylogenetic relationships withinTaenia taeniaeformis variants and other taeniid cestodes inferred from the nucleotide sequence of the cytochromec oxidase subunit I gene

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Abstract
Nucleotide sequence variations in a region of the mitochondrial cytochromec oxidase subunit I (COI) gene (391 bp) were examined within seven species of the genusTaenia and two species of the genusEchinococcus, including ten isolates ofT. taeniaeformis and six isolates ofE. multilocularis. More than a 12% rate of nucleotide differences between taeniid species was found, allowing the species to be distinguished. InE. multilocularis, no sequence variation was observed among isolates, regardless of the host (gray red-backed vole, tundra vole, pig, Norway rat) or area (Japan, Alaska) from which each metacestode had been isolated. In contrast, six distinct sequences were detected among the tenT. taeniaeformis isolates examined. The level of nucleotide variation in the COI gene withinT. taeniaeformis isolates except for one isolate from the gray red-backed vole (TtACR), which has been proposed as a distinct strain or a different species, was about 0.3%–4.1%, whereas the COI gene sequence for TtACR differed from those of the other isolates, with levels being 9.0%–9.5%. Phylogenetic trees were then inferred from these sequence data using two different algorithms.