The trematode genera Paragonimus and Schistosoma in East Asia: molecular evolution, phylogeny and biogeography

Trematode infections affect one fifth of the worlds' population, with more than 200 million Chinese alone being at risk (World Health Organisation 1997, Hotez et at 1997). Of particular interest to this study are the Asian species of the trematode genera Paragonimus and Schistosoma, which infect many mammals, including humans. It is becoming clear that within both genera species complexes exist that require further characterisation. Molecular markers have given some insight into the nature of these complexes. In this thesis additional molecular markers are investigated as sources of information about the nature and distribution of the S. japonicum, P. westermani and P. ohirai species complexes. These two genera are of additional interest because they are thought to have shared a similar biogeographic history in Asia, which should be reflected in their molecular evolution. I have obtained DNA sequences from one nuclear (ITS1) and one mitochondrial (ND1) marker of five Paragonimus species (P. westermani, P. miyazakii, P. macrorchis, P. ohirai and P. iloktsuenensis) present in East Asia, including numerous geographic isolates of the P. westermani and P. ohirai species complexes. In addition, I have obtained ITS1 sequences of three schistosome species (S. japonicum, S malayensis and S. mekongi) present in East Asia, which comprise the S. japonicum species complex and an African schistosome species (S. mansoni) for comparative purposes. I could differentiate all species using ITS1 and ND1 sequence data. ITS1 is contained within the ribosomal DNA gene cluster, which is repeated in tandem many times. ITS1 does not experience the constraints of coding regions and theoretically undergoes sequence homogenisation within individuals and species. Despite this, intra-individual sequence variation was sometimes greater than inter-species variation, particularly among northeast Asian P. westermani isolates. Such variation confounded phylogenetic inferences for this group. There are some interesting aspects relating to processes ...