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

Abstract

Species of the viviparous monogenean genus Gyrodactylus are difficult to identify morphologically and relationships within the genus are unclear. Partial or complete sequences were obtained for the internal transcribed spacers (ITS-1 and ITS-2) and 5.8S ribosomal DNA (rDNA) of 11 Gyrodactylus species (G. kobayashii, G. gurleyi, G. pungitii, G. rogatensis, G. gasterostei, G. derjavini, G. salaris, G. rarus, G. turnbulli, G. bullatarudis, and G. arcuatus) and the related Gyrdicotylus gallieni. Phylogenetic analyses (parsimony, distance, and maximum likelihood) separated species of the Gyrodactylus wageneri species-group (with a long ITS-1) from those of the Gyrodactylus eucaliae and G. arcuatus species-groups (with a short ITS-1). This subdivision 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 species group, as this species clustered within the G. wageneri group. The morphologically homogeneous G. wageneri group was subdivided by our molecular data 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 informative indicator of phylogenetic relationships within the genus Gyrodactylus. The potential importance of this technique for future gyrodactylid systematics is discussed.