Esociform phylogeny

Despite numerous studies aimed at resolving relationships among basal euteleost lineages, many aspects of their phylogeny remain the subject of debate. The Esociformes have proven particularly difficult to place, and although a hypothesis of relationships within this group first proposed by Nelson has been generally accepted, a recent hypothesis based on evidence from mitochondrial DNA sequences is not congruent with it. We have assembled an expanded dataset of DNA sequences from the mitochondrial and nuclear genomes to test existing hypotheses of esociform inter- and intraordinal relationships. This dataset includes representatives from all extant esociform lineages and a wide diversity of potential outgroups (51 taxa in total). We also conducted a review of the morphological information that supports currently held hypotheses of esociform inter- and intraordinal relationships. This review revealed potential problems with character state coding and interpretation of character states. However, the molecular evidence, particularly the nuclear sequences, produced unambiguous support for a sister-group relationship between esociforms and salmonoids; and also offer similarly strong corroboration of the hypothesis of esociform intraordinal relationships based on mitochondrial sequences and for the monophyly of the subgenera Esox and Kenoza of Esox. In addition to the conclusions regarding esociform relationships, the molecular evidence we present offers support for the monophyly of the Osmeridae, for a sister-group relationship between the Retropinnidae and the Osmeroidei (Osmeridae + Salangidae + Plecoglossidae) and for a close relationship of Stomiiformes and Osmeriformes.