Phylogenetic analysis of Gyrodactylus spp. (Platyhelminthes : Monogenea) using ribosomal DNA sequences

Species of the viviparous monogenean genus Gyrodactylus are difficult to id entify morphologically and relationships within the genus are unclear. Part ial or complete sequences were obtained for the internal transcribed spacer s (ITS-1 and ITS-2) and 5.8S ribosomal DNA (rDNA) of 11 Gyrodactylus specie s (G. kobayashii, G. gurleyi, G. pungitii, G. rogatensis, G. gasterostei, G . derjavini, G. salaris, G. rarus, G. turnbulli, G. bullatarudis, and G. ar cuatus) and the related Gyrdicotylus gallieni. Phylogenetic analyses (parsi mony, distance, and maximum likelihood) separated species of the Gyrodactyl us wageneri species-group (with a long ITS-1) from those of the Gyrodactylu s eucaliae and G. arcuatus species-groups (with a short ITS-1). This subdiv ision into species with a long (610-630 base pairs (bp)) or short (300-500 bp) ITS-1 was also apparent with 5.8S rDNA and ITS-2 data. No support could be found for the hypothesis that G. salaris is a member of a separate spec ies group, as this species clustered within the G. wageneri group. The morp hologically homogeneous G. wageneri group was subdivided by our molecular d ata into five species that infect cottids, gasterosteids, and salmonids and two species that infect cyprinid fishes. Overall, the ITS-2, combined with the 5.8S rDNA (an alignment of 668 bp), appeared to be the most informativ e indicator of phylogenetic relationships within the genus Gyrodactylus. Th e potential importance of this technique for future gyrodactylid systematic s is discussed.