Phylogenic Analysis Inferred From 28S RDNA And ITS-5.8S RDNA Data On Four Species Of Myxosporeans (Myxozoa: Myxosporea)

In this study, Large subunit rDNA (28S rDNA) partial sequence and ITS-5.8 S rDNA complete sequence for four species (belonging to 3 genera) of Myxosporeans were detemined. They are Unicauda pelteobagrs, Myxobolus branchicola sp. nov., Myxobolus ampullicapsulatus (3 populations), and Henneguya doneci (2 population). The phylogeny of 4 Myxosporeans were deduced based on these two sequences, 28S rDNA and ITS-5.8 S rDNA, with maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods.In the present resaerch, the evolutionary trends within species, genera and populations of myxosporeans by using 28S rDNA were investigated:①Results of 28S rDNA phylogeny and 18S rDNA phylogeny were similar, indicating they first cluster marine and freshwater lineages, and both in marine and freshwater lineages, generas of Myxidium and Zschokkella grouped into one clade;②Phylogenetic analyses of the 28S rDNA sequence, genetic distance and 28S rDNA sequence D2, D8 and D10 length variations indicates Myxobolus, Henneguya and Unicauda species could possess a common origin, but also need to be further confirmed;③Tissue specificity is often discussed in phylogenetic of the 18S rDNA sequence, but in cladistic tree of the 28S rDNA sequence, tissue specificity is not significant;④The result of analysis genetic distance of M. ampullicapsulatus (3 populations) show that: The differences of 2 populations host in goldfish and Carassius aumtus in Yongchuan are small, and these 2 populations are relatively large differences from population host in Cyprinus carpio in Hejiang. This result shows: 28S rDNA sequence can be well used in the discrimination at the under-species level.Also, by using ITS-5.8S rDNA the evolutionary trends within species, genera and populations of myxosporeans were investigated:①ITS1 and ITS2 sequence of myxosporeans may be used to construct the phylogenetic tree for relatively lower taxa (such as populations);②On the contrary, 5.8S rDNA sequence is more relatively suitable for construct the phylogenetic tree for relatively higher taxa;③It is further confirmed that myxosporeans are a class of metazoan by phylogenetic analyses of the 5.8S rDNA sequence;④Results of ITS-5.8S rDNA phylogeny are similar to 18S rDNA and 28S rDNA phylogeny, indicating they first cluster marine and freshwater lineages;⑤Conclusion of inference GC value is correspondence with the result of phylogenetic analyses by study between phylogenetic analyses of the 5.8S rDNA sequence and GC content in species of ITS-5.8S rDNA phylogeny;⑥Genetic distance result of ITS-5.8S rDNA is more large than Genetic distance result of 18S rDNA and 28S rDNA, but The view they imply are same. This result shows: ITS-5.8S rDNA sequence can distinguish species and under-species level.