Studies on origin and coevolution of Schistosoma japonicum in Asia

迄今为止，为了研究血吸虫属的起源，血吸虫属之间的系统发育关系已估计使用部分核苷酸序列的CO 1，1 srDNA和ITS 2。本研究首次测定了中国血吸虫CO 1、1 srDNA和ssrDNA的全序列，并根据序列信息推测了中国血吸虫科各种间的系统发育关系。本研究共采集了10属29种血吸虫，其中体血吸虫亚科6属，裂体血吸虫亚科2属，巨裂体血吸虫亚科2属。血蝎科的银鲛属被用作外群。CO 1、ssrDNR和1 srDNA的核苷酸长度分别为1122 bp和3765 bp。在这项研究中，包括所有三个基因的组合核苷酸序列用于树分析。由于（鸟毕吸虫+澳毕吸虫）的包被支持为（血吸虫+东毕吸虫）的姐妹包被，因此推测该虫为并系。东毕吸虫也被归入血吸虫属，是非洲血吸虫和印度血吸虫的姊妹种。这一结果表明东毕吸虫可能是它们的祖先种。一种是Davis（1980，1992）提出的非洲起源说，认为从冈瓦纳大陆分离出来的印度大陆板块将血吸虫的一个祖先种从非洲带到了亚洲。另一种是亚洲起源理论（Snyder & Loker，2000; Agatsma et al.，2003年; Jiang et al.，2004年）提出血吸虫的祖先物种发生在亚洲，并通过哺乳动物宿主的迁移将亚洲扩展到非洲。本研究再次支持亚洲起源说。

To date, in order to examine the origin of the genus Schistosoma, phylogenetic relationships among the genus Schistosoma have been estimated using partial nucleotide sequences of CO1, 1srDNA and ITS2. In this study, whole nucleotide sequences of CO1, 1srDNA aqnd ssrDNA were determined for the first time, and on the basis of the sequence information, phylogenetic relationships were inferred among species from the family Schistosomatidae. Materials used in this study are in total 29 species in 10 genera consisting of 6 genera from the subfamily Schistosomatinae, two genera from the subfamily Bilharziellinae and two genera from the subfamily Gigantobilharziinae. The genus Chimaerohemecus in the family Sanguinicolidae was used as an outgroup. The number of nucleotides determined for CO1, ssrDNR and 1srDNA was 1122 bp and 3765 bp, respectively. In this study, combined nuleotide sequences including all of the three genes were used for tree analysis. It was estimated that the mammalianschistosomes were paraphyletic, since the clad of (Ornithobilharzia+Austrobilharzia) was supported to be a sister clad of (Schistosoma+Orientobilharzia). It was also found that Orientobilharzia was placed within the genus Schistosoma, and a sister of clad consisting of the African group and the S.indicum group. This result suggests that Orientobilharzia could be an ancestral species for them.There are two theories on the origin of Schistosoma. One is the African origin theory by Davis (1980,1992), proposing that Indian continental plate, which separated from the Gondwana Land, carried an ancestral species of Schistosoma from Africa to Asia. Another is the Asian origin theory (Snyder & Loker,2000; Agatsma et al., 2003; Locker et al., 2004) proposing that an ancestral species of Schistosoma occurred in Asia and expanded Asia to Africa through migration of a mammalian host. The present study supported the Asian origin theory again.