Phylogeny and biogeographic history of hake (genus Merluccius), inferred from mitochondrial DNA control-region sequences

Phylogenetic analyses of the left domain of the mitochondrial DNA control-r egion sequence have been used to examine the relationships among species of the genus Merluccius (Rafinesque, 1810), and to compare these with hypothe ses based on morphological, meristic and allozyme characters. Analysis of a ligned sequences revealed that transition bias was much lower than in mamma lian mtDNA, and that nucleotide composition of control-region sequences was biased toward A and T. We have roughly calibrated a molecular clock for th e genus, based on the rise of the Isthmus of Panama, which is believed to h ave created a barrier to dispersal between marine species of the Atlantic a nd Pacific Oceans. Our mtDNA-based phylogeny was highly congruent with allo zyme-based phylogenies, but poorly so with a previously described phylogeny based on morphology. Specifically, our phylogeny resolved two well-support ed principal clades, one of American (west Atlantic and east Pacific) speci es and the other of Euro-African least Atlantic) species. This suggests an evolutionary history during which the ancestral lineage of Merluccius was d ivided between two geographic regions, with subsequent dispersal and vicari ant events resulting in the evolution and distribution of extant taxa. Howe ver, the relationships between some taxa within the American clade could no t be resolved. We suggest that this is consistent with an hypothesis of a r apid origin and radiation of these taxa.