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，利用CO1、1srDNA和ITS2的部分核苷酸序列估计了血吸虫属之间的系统发育关系。本研究首次测定了血吸虫科CO1、1srDNA和ssrDNA的全核苷酸序列，并根据序列信息推测了种间的系统发育关系。本研究所用材料共10属29种，其中血吸虫亚科6属，血吸虫亚科2属，巨型血吸虫亚科2属。以血血科Chimaerohemecus属作为外类群。CO1、ssrDNR和1srDNA的核苷酸数量分别为1122 bp和3765 bp。本研究采用包含所有三个基因的组合核苷酸序列进行树状分析。由于（ornithobilharziia + austrobilharziia）的包层是（Schistosoma+ orientobilharziia）的姐妹包层，推测该哺乳动物血吸虫为副绦虫。东方血吸虫属血吸虫属，是由非洲血吸虫属和印度血吸虫属组成的姐妹血吸虫属。这一结果表明，东方菌可能是它们的祖先种。关于血吸虫的起源有两种说法。一种是Davis（1980,1992）提出的非洲起源理论，认为从冈瓦纳大陆分离出来的印度大陆板块将一种血吸虫的祖先物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; Locker et al., 2004），提出血吸虫的一个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.