Taxonomy of selected species of Myxobolus (Myxozoa) from freshwater fishes in Canada : applications of light microscopy and molecular methods

Abstract

Species of Myxobolus (Myxozoa) are compared on the basis of spore morphology, site of development, host species and sequence data of the 18S rDNA. The first situation compares the morphology and molecular features of Myxobolus procerus from large intercellular and small intracellular cysts in trout-perch ( Percopsis omiscomaycus ) muscle. The data suggests that spores from each cyst type represent a single species of Myxobolus with variable cyst phenotypes. Interestingly, spores from the small cysts were shorter than those from the large cysts implying ecophenotypic variation. The fact that the two cyst types did not occur independently of each other suggests that they are a single species. The observed differences in the morphological and molecular data suggest species divergence. The second situation provides a comparison between Myxobolus neurophilus from the optic tectum of yellow perch ( Perca flavescens ) and specimens that were tentatively identified as M. neurophilus from the tectum of Johnny darter ( Etheostoma nigrum ). Although the morphology of the spores of these samples is very similar, molecular information identifies the latter parasite as a possible new species of Myxobolus . The morphological and molecular similarities between these three species are examined on both an individual basis and between other species in the genus Myxobolus . Phylogenies are drawn from the molecular data and a phylogenetic tree is constructed that includes sequences presented in the current work which have not been analysed at this level. The validity of traditional taxonomic methods and their use in classification of the myxobolids is discussed. Alternately modern techniques of molecular biology and their role in the taxonomy of these parasites are evaluated.