Studies on speciation of Asian schistosomes

亚洲血吸虫吸虫的系统发育至今仍不清楚。本研究应用PCR技术对日本血吸虫、湄公河血吸虫和马来西亚血吸虫三种亚洲血吸虫进行了分子遗传学分析。扩增细胞色素C氧化酶亚基I（COI）基因片段，并将其克隆到TA载体中。使用ABI测序仪/染料引物法。总共对395个碱基对进行测序，并使用Paup（最大简约法）和Clustal V（相邻连接法）进行分析。作为外群，使用了两个非洲物种，S.mansoni和S.haematobium。两种方法构建的系统发育树相同。即湄公河血吸虫和马来西亚血吸虫先聚在一起，再与日本血吸虫汇合。染色体C-带带型分析表明，湄公中华绒螯蟹与马来中华绒螯蟹的亲缘关系较近，支持了本研究建立的分子系统树。本文对螺类的宿主种，罗氏螺、开新锥螺和感病钉螺进行了核型分析。结果表明，染色体数目均为2n=34，但性染色体分别为XY型和XO型。在感染实验中，对钉螺的性染色体未发生分化。使用了三种日本螺，即Oncomelania nosophora、O.minima和Bythinella nipponica。结果表明，只有钉螺对日本血吸虫和马来西亚血吸虫敏感。

Phylogeny among Asian Schistosoma flukes have not been known so far. In the present study, PCR technique was used to make up a molecular phylogeny on three Asian Schistosoma species, S.japonicum, S.mekongi, and S.malaynsis. A region of cytochrome C oxidase subunit I (COI) was amplified, and the fragment was cloned into TA-vector. The ABI sequencer/the Dye primer method were used. In total, 395 base pairs were sequenced, and analyzed with Paup (Maximum Parsimony Method) and Clustal V (The Neighbor-Joining Method). As outgroups, two African species, S.mansoni and S.haematobium were used. Both of the two methods constructed the same phylogenetic trees. That is, S.mekongi and S.malaynsis was clustered first, and joined with S.japonicum. The two African species were joined into a cluster, and bound with the Asian species.C-banding pattern analysis of the chromosomes was also performed The pattern showed closer relationships between S.mekongi and S.malaynsis, supporting the molecular phylogenetic tree obtained in this study. Karyotypic analysis of the snail host species, Robertsiella gismani, Neotricula aperta, and Oncomelania nosophora were carried out. It was found that chromosome numbers were all 2n=34, but sex chromosomes seem to be of XY type and XO type for Robertsiella gismani and Neotricula aperta, respectively. In the case of Oncomelania nosophora, no sex chromosome differenciation occurred.Infection experiments were also carried out. Three Japanese snails, Oncomelania nosophora, O.minima and Bythinella nipponica were used. It was found that only Oncomelania nosophora was susceptible to S.japonicum and S.malaynsis infection.