|Budget Amount *help
¥11,100,000 (Direct Cost: ¥11,100,000)
Fiscal Year 2003: ¥3,700,000 (Direct Cost: ¥3,700,000)
Fiscal Year 2002: ¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2001: ¥3,800,000 (Direct Cost: ¥3,800,000)
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.