Estimated molecular phylogenetic relationships of six siphonostomatoid families (Copepoda) symbiotic on elasmobranchs

Members of the Siphonostomatoida are associated with either invertebrates or vertebrates. Even though the interfamilial relationships within the Siphonostomatoida are unresolved, it has generally been assumed that those members parasitic on vertebrates form a derived and monophyletic group. Eleven of the families symbiotic on vertebrates have been reported from elasmobranchs. One nuclear genetic marker (18S rDNA) and two partial mitochondrial markers (16S rDNA and COI) were used to estimate the phylogenetic relationship among six families symbiotic on elasmobranchs. The estimated molecular topologies using maximum likelihood, parsimony (unweighted and weighted), and Bayesian analyses are mostly similar. The six families investigated grouped into two major clades, with Kroyeriidae, Caligidae, Pandaridae, and Dichelestiidae in one clade, and Eudactylinidae and Sphyriidae in the other. The molecular topologies are compared with the previous morphological topology and present some support for some of the proposed relationships and alternative hypotheses in the areas of conflict. Valuable information obtained from the study is the indication that the genes used are informative at this level of investigation and can therefore be used in more elaborate future studies. © 2009 Brill Academic Publishers.