Abstract
The molecular phylogeny of Gyrodactylus salmonis from brook charr, Salvelinus fontinalis , rainbow trout, Oncorhynchus mykiss , cutthroat trout, O. clarkii , and Atlantic salmon, Salmo salar , in Canada is presented using sequences from ITS‐rDNA and the mitochondrial COX 1 gene. Sequence variation among G. salmonis specimens from the different North American hosts was consistent with within‐species variation reported for other Gyrodactylus . Sequence data are compared to those from other members of the wageneri group parasitizing salmoniform fishes in northern Europe ( G. derjavini , G. derjavinoides , G. lavareti , G. salaris , G. salvelini , G. teuchis and G. truttae ) and Asia ( G. brachymystacis ). Sequence divergence between G. salmonis and the recently described G. salvelini on Arctic charr, Salvelinus alpinus , in Finland was consistent with within‐species levels of variation in Gyrodactylus ; however, phylogenetic analyses and morphological comparisons provided evidence of their distinctiveness such that they appear to be sister species. They grouped with G. lavareti (a parasite of a coregonid) to form a clade separate from European and Asian species of the wageneri lineage known from salmonid fish. Further study of gyrodactylids from across salmonid, coregonid and thymallid fish in the northern hemisphere would shed more light on the phylogeography of these parasites and serves as an important backdrop to understanding the evolution of their emergent virulence.