Molecular evolution, systematics, and zoogeography of the rockfish subgenus Sebastomus (Sebastes, Scorpaenidae) based on mitochondrial cytochrome b and control region sequences.

Sebastomus is one of the most species-rich subgenera of Sebastes, whose monophyly is well supported by morphological and molecular data. We present the first description of the complete nucleotide sequence of the mitochondrial cytochrome b gene and the partial sequence of the control region of the 14 species of Sebastomus. We used these data in phylogenetic analyses to investigate their evolutionary relationships. Extremely low levels of sequence divergence indicated a recent ancestry of these species, suggesting a very rapid radiation within the last million years. The molecular data revealed two main clades within Sebastomus, each with species of different affinities that invaded new habitats from the subgeneric center of distribution. The rapid speciation in this lineage was manifested in the poor resolution of some nodes in the phylogeny. Internal fertilization and viviparity in Sebastes may have played an important role in the sudden acquisition of reproductive barriers during its radiation. The mitochondrial DNA data suggest that prolific speciation in Sebastomus may have been associated with rapid lineage sorting punctuated by allopatric reproductive isolation subsequent to dispersal events and, perhaps, by sympatric reproductive isolation associated with internal fertilization.