Studies on speciation and its origin of Schistosoma japonicum

1.分别对采自孟加拉国、印度尼西亚、斯里兰卡和泰国的印度血吸虫、斯里兰卡血吸虫和泰国血吸虫的CO1、28S和ITS2的核苷酸序列进行了分析，并用NJ法、UPGMA法和简约法进行了系统发育分析。得到如下结果：(L)S.indum和S.Spindale与来自非洲的S.haematobium及其相互之间关系密切，而S.nasale与S.mansoni有亲缘关系。2)南方链霉菌距离包括印度链霉菌群和非洲种的其他三种的聚集区较远。2.原属于血吸虫属的象血吸虫Bivitellobilharzia Nairi在分子水平上也与血吸虫有亲缘关系。3.对斯里兰卡和孟加拉国的钉螺宿主I.exustus和Lymna ea spp.的ITS2和28S区的核苷酸序列进行了分析，发现I.exustus与Biomphalaria spp.有较强的亲和力。而不是Lymnaea spp.4.染色体C-显带分析表明，7对常染色体和性染色体(Z和W)具有种特异性，亚洲血吸虫和非洲血吸虫之间存在较大差异。特别是2号染色体AM倒位的研究结果表明，亚洲的日本血吸虫为原始型，而非洲种为衍生型。5.作为一种假说，1)血吸虫的祖先物种在数千万年前从亚洲的双黄球藻分化而来，并产生了两个物种复合群：中华血吸虫和印度血吸虫。2)日本血吸虫群来源于中华血吸虫的祖先种，适应一种新的钉螺宿主。3)印度钉螺种群的祖先物种适应了新的钉螺宿主--印度钉螺，以未知的方式迁徙到非洲大陆，形成了非洲物种的祖先物种。

1. Nucleotide sequences of CO1, 28S and ITS2 were examined for samples from four species of the S.indicum group, Schistosoma indicum, S.spindale, S.nasale, S.incognitum collected from Bangladesh, Indonesia, Sri Lanka and Thailand, respecitively, and the NJ, UPGMA and Parsimony methods were used for phylogenetic analyses. The following results were obtained ; l)S.indicum and S.spindale were closely related to S.haematobium from Africa and to each other, while S.nasale has affinity with S.mansoni. 2) S.incognitum lies distant from the cluster that includes other three species of the S.indicum group and the African species. 2. A elephant schistosomes, Bivitellobilharzia nairi that belonged to the genus Schistosoma formerly, was found to show affinity to the Schistosoma species in a molecular level as well. 3. Nucleotide sequences of snail hosts in Sri Lanka and Bangladesh, I.exustus and Lymnaea spp., were also analyzed for the ITS2 and 28S regions, and found that I.exustus has a stronger affinity to Biomphalaria spp. than to Lymnaea spp. 4. Chromosomal analysis for the C-banding pattern showed that seven pairs of autosomes and sex chromosomes (Z and W) were species-specific, and large differences exist between Asian and African species of Schistosome. In particular, findings of AM inversion of chromosome 2 suggests that S.japonicum in Asia is of original type, while the African species, of derived type. 5. As a hypothesis, 1) Ancestral species of Schistosoma was diverged from Bivitellobilharzia nairi in Asia tens of millions years ago, and produced two species complex group, the S.sinensium and S.indicum group. 2) The S.japonicum group arose from ancestral species of the S.sinensium, adapting a new snail host, Oncomelania. 3) Ancestral species of the S.indicum group, adapting to a new snail host, Indoplanorbis, migrated into the African continent due to an unknown way, and gave rise to ancestral species of the African species.