Phylogenetic Study Of Parasitic Copepods In The Ergasilidae And Lernaeidae On Freshwater Fish In China

Copepods in the Ergasilidae (Copepoda: Poecilostomatoida) and Lernaeidae (Copepoda: Cyclopoida) are two major groups of parasitic copepods on freshwater fish. The present study aimed to illustrate the phylogenetic relationship among species in the families Ergasilidae and Lernaeidae, and to understand the phylogenetic relationship among three species in the Sinergasilus (Ergasilidae) with the analysis of the Sinergasilus-host co-evolutionary relationship.A total of 14 species belonging to 4 genera in the Ergasilidae and 3 species to 2 genera in the Lernaeidae were obtained from 24 species of fish in China, and the 18S, 28S rDNA sequences were cloned from the collected parasitic copepods. Phylogenetic analyses using partial 18S and partial 28S rDNA sequences and combined 18S-28S rDNA sequences suggested that both Ergasilidae and Lernaeidae are monophyletic. In the Ergasilidae, the genera Sinergasilus and Paraergasilus are monophyletic, and Ergasilus is paraphyletic. Except the uncertain position of E. scalaris and E. yaluzangbus, copepods in the Ergasilidae can be further separated into three main clades, i.e. the Sinergasilus-Eragsilus clade including species in the Sinergasilus and E. anchoratus in the Ergasilus, the Pseudergasilus-Ergasilus clade including P. parasiluri in the Pseudergasilus and some in the Ergasilus, and the Paraergasilus-Ergasilus clade including species of Paraergasilus and E. peregrinus in the Ergasilus. All the three trees generated by using maximum parsimony, neighbor-joinning and Bayesian inference methods support thePseudergasilus-Ergasilus clade has a closer phylogenetic relationship with the Sinergasilus-Eragsilus clade based on 18S rDNA,and a closer relationship with the Paraergasilus-Ergasilus clade based on 28S rDNA sequences. The evolutionary rule...