A molecular and morphological perspective on the phylogenetic relationships of the otophysan fishes.

We examined the phylogenetic relationships among the major lineages of otophysan fishes (Cypriniformes, Characiformes, Siluroidei, and Gymnotoidei) using a combined analysis of molecular and morphological characters. The molecular characters comprised 160 phylogenetically informative sites from nuclear-encoded ribosomal RNA and 208 phylogenetically informative sites from the mitochondrial genes encoding ribosomal RNA and the valine transfer RNA for nine otophysan taxa and a gonorynchiform outgroup. The morphological data comprised 85 characters that were obtained from an earlier cladistic study. Congruence among molecular and morphological characters is generally high. The combined analysis supports a sister group relationship between the Gymnotoidei and Siluroidei, which together form a sister group to the Characiformes. The separation of the Cypriniformes from all other otophysans represents the earliest phylogenetic split within the Otophysi. Despire the generally high congruence among molecular and morphological characters, the molecular data analyzed separately produce a topology that differs from the analysis of the combined data. Sources of the taxonomic incongruence between the molecular and morphological data are examined.