Molecular phylogenetic examination of the Delphinoidea trichotomy: Congruent evidence from three nuclear loci indicates that porpoises (Phocoenidae) share a more recent common ancestry with white whales (Monodontidae) than they do with true dolphins (Delphinidae)

Porpoises (Phocoenidae), dolphins (Delphinidae), and the two species of Mon odontidae (beluga and narwhal) together constitute the superfamily Delphino idea. Although there is extensive evidence supporting the monophyly of this superfamily, previous studies involving morphology, as well as sequence an alysis of mitochondrial genes, have failed to yield a clear picture of the relative relationships within the group. Here we present the first examinat ion of this issue from the perspective of single-copy nuclear genes at the DNA sequence level. The data involve three such loci: von Willebrand factor (vWF), interphotoreceptor retinoid binding protein (IRBP), and lactalbumin . The vWF and IRBP data sets consist of protein-coding fragments, whereas t he sequenced lactalbumin fragment is predominately intronic, All phylogenet ic analyses involving at least one representative from each of the three De lphinoidea families congruently support a beluga/porpoise clade. The levels of sequence divergence for most of these data appear to roughly concur wit h a paleontological date for the radiation of the Delphinoidea at 11-15 MYA but, in agreement with mitochondrial DNA sequence analyses, suggest that t he extant major groups of cetaceans radiated approximately 25 MYA, 10 milli on years later than inferred from paleontological data. (C) 2000 Academic P ress.