MOLECULAR PHYLOGENY OF MICROSPORIDIANS WITH PARTICULAR REFERENCE TO SPECIES THAT INFECT THE MUSCLES OF FISH

Ribosomal DNA from eight species of microsporidians infecting fish hav e been sequenced. Seven of these species infect the skeletal muscle of fish (Pleistophora spp.) and one species infects migratory mesenchyma cells (Glugen anomala). These sequences, in addition to other availab le microsporidian rDNA sequences from a broad range of host taxa, have been used in phylogenetic analysis. This analysis revealed that muscl e-infecting microsporidians from fish are a polyphyletic group, indica ting that characters supposed to be important in the classification of the genus Pleistophora have to be re-evaluated. One character that pr obably has a polyphyletic origin is the amorphous coat, which has been extensively used in the definition of this genus. Furthermore, our re sults showed that the insect parasitizing Pleistophora spp. are not re lated to the true pleistophorans parasitic in skeletal muscle of fish. Phylogenetic analysis of small subunit rDNA sequences revealed disagr eements between the molecular phylogeny and classifications based upon ultrastructure. Many of the morphological characters claimed to be im portant in microsporidian classifications appeared to have arisen seve ral times during evolution: for example, the diplokaryon and sporophor ous vesicles.