Phylogeny and phylogeography of Atlantic oyster species: evolutionary history, limited genetic connectivity and isolation by distance

The phylogenetic relationships between naturally occurring AtlanticCrassostreaoyster species were inferred through analyses of mitochondrial (cytochrome oxidase subunit I and 16S) and nuclear (second internal transcribed spacer) sequences. We also scored 15 allozyme loci on 422 oysters to study population structuring ofC. rhizophoraeandC. brasilianaalong 9000 km of the Western Atlantic coastline. Despite morphological similarities,C. virginicawas genetically more closely related toC. rhizophoraethan toC. brasiliana. In contrast,C. paraibanensiswas genetically indistinguishable fromC. brasiliana, which is probably a junior synonym of the AfricanC. gasar. Significant genetic differentiation between populations ofC. rhizophoraeandC. gasarwere found along the Western Atlantic coast, supporting an isolation-by-distance pattern.