Phylogeography of Ophioblennius: The role of ocean currents and geography in reef fish evolution

Many tropical reef fishes are divided into Atlantic and East Pacific taxa, placing similar species in two very different biogeographic regimes. The tr opical Atlantic is a closed ocean basin with relatively stable currents, wh ereas the East Pacific is an open basin with unstable oceanic circulation. To assess how evolutionary processes are influenced by these differences in oceanography and geography, we analyze a 630-bp region of mitochondrial cy tochrome b from 171 individuals in the blenniid genus Ophioblennius. Our re sults demonstrate deep genetic structuring in the Atlantic species, O. atla nticus, corresponding to recognized biogeographic provinces, with divergenc es of d = 5.2-12.7% among the Caribbean, Brazilian, St. Helena/Ascension Is land, Gulf of Guinea, and Azores/Cape Verde regions. The Atlantic phylogeny is consistent with Pliocene dispersal from the western to eastern Atlantic , and the depth of these separations (along with prior morphological compar isons) may indicate previously unrecognized species. The eastern Pacific sp ecies, O. steindachneri. is characterized by markedly less structure than O . atlanticus, with shallow mitochondrial DNA lineages (d(max) = 2.7%) and h aplotype frequency shifts between locations in the Sea of Cortez, Pacific P anama, Clipperton Island, and the: Galapagos Islands. No concordance betwee n generic structure and biogeographic provinces was found for O. steindachn eri. We attribute the phylogeographic pattern in O. atlanticus to dispersal during the reorganization of Atlantic circulation patterns that accompanie d the shoaling of the Isthmus of Panama. The low degree of structure in the eastern Pacific is probably due to unstable circulation and linkage to the larger Pacific Ocean basin. The contrast in genetic signatures between Atl antic and eastern Pacific blennies demonstrates how differences in geology and oceanography have influenced evolutionary radiations within each region .