Studies on speciation and its origin of Schistosoma japonicum

1. 对分别采集于孟加拉国、印度尼西亚、斯里兰卡和泰国的4种籼稻血吸虫（Schistosoma indicum）、spindale血吸虫、nasale血吸虫、incognitum血吸虫进行CO1、28S和ITS2核苷酸序列分析，并采用NJ、UPGMA和Parsimony方法进行系统发育分析。得到以下结果：l)。indicum和spindale与非洲的s.a haematobium亲缘关系较近，而s.a nasale与s.a mansoni亲缘关系较近。2) incognitum与包括籼稻组其他3种和非洲种在内的类群相距较远。2. 以前属于血吸虫属的大象血吸虫Bivitellobilharzia nairi也被发现在分子水平上与血吸虫物种有亲缘关系。3. 对斯里兰卡和孟加拉国的蜗牛寄主I.exustus和lynaea spp的ITS2和28S区域的核苷酸序列进行分析，发现I.exustus与Biomphalaria spp的亲缘性比与lynaea spp的亲缘性强。c带型染色体分析显示，7对常染色体和性染色体（Z和W）具有种特异性，亚洲和非洲种间存在较大差异。特别是2号染色体AM反转的结果表明，亚洲种为原始型，而非洲种为衍生型。5. 作为假设，1)数千万年前，血吸虫的祖先种从亚洲的Bivitellobilharzia nairi分化而来，产生了s.s sinensium和s.s indicum两个物种复合体群。(2) s.a japonicum类群由s.a sinensium的祖先种进化而来，适应了新的蜗牛寄主Oncomelania。(3)s.a indicum类群的祖先种，适应了新的蜗牛寄主Indoplanorbis，以未知的方式迁移到非洲大陆，并产生了非洲种的祖先种。

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.