| Research Abstract |
Life cycles of cestodes are maintained by predator-prey relationship. In the evolution of cestodes, not only coevolution but also host exchange in response to environmental changes would be important driving forces of diversification. In this study, experimental parasitisms of ecologically isolated hosts and parasites were analyzed in terms of evolutional trace. Furthermore, field survey was carried out to analyze adaptation mechanisms of cestodes.
Seven species of Taenia (including 10 isolates of T.taeniaeformis (Tt) ) and two of Echinococcus (including 6 isolates of E.multilocularis (Em) ) were comprehensively compared in terms of morphology, host specificity, protein composition, isoenzyme pattern, DNA restriction endonuclease analysis, DNA fingerprinting and nucleotide sequence analysis of the cytochrome c oxidase subunit I (COI) gene.
In Tt, one isolate showed distinct differences from others in hook morphology, intermediate host specificity and COI gene sequence. It is concluded th
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at there are two distinct Tt strains in Hokkaido. One is genetically and biologically close to the cosmopolitan strain found in the house mice and rats. The other is totally different and found in Clethrionomys. It is hypothesized that Clethrionomys strain was originally introduced into Hokkaido by an extinct feline animal and survived through host exchange to domestic cats. The discovery of this strain is important for taeniid cestode phylogeny study.
In a field survey, Em was found in rats ; a first record in Japan. Based on this finding, rats may play a role in maintaining Em life cycle in Hokkaido. However, DNA analysis of this isolate revealed no difference with others found in voles. Therefore, Em prevalent in Hokkaido is a genetically close population. Moreover, the populations in Hokkaido and St. Lawrence Island (USA) were found to be genetically close. It is speculated that Em prevalent in Hokkaido was originally introduced from Alaska and then rapidly expanded its distribution. Less
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