Molecular phylogenetics reveals first record and invasion of Saccostrea species in the Caribbean

Taxonomic uncertainty often limits our ability to resolve biogeographic patterns and discern biological invasions. Within the bivalve mollusks, this uncertainty is particularly acute for oysters, as the high degree of phenotypic plasticity of their shells creates taxonomic confusion. The integration of molecular data with shell morphology can differentiate species, providing new insights into biogeography, invasions, and ecology of this functionally important group. As an initial step in resolving the identities and current geographic distributions of oyster species, sequence data from the mitochondrial cytochrome oxidase I gene were combined with morphological criteria to confirm the identities of ten oyster species of Ostreidae, Isognomonidae, and Pteriidae, focusing on the Pacific and Caribbean coasts of Panama, since tropical biota have received the least study. The results indicate that Crassostrea virginica, previously only reported from this region along the Yucatan Peninsula and coast of Venezuela, also occurs in the Caribbean waters of Panama. We also document the first record for a species of Saccostrea, a genus native to the Pacific, suggesting an invasion by an unknown non-native Saccostrea species that is now widespread along the Caribbean from the Panama Canal west to Bocas del Toro. Sequences of the internal transcribed spacer region (ITS1) of the ribosomal gene complex (rDNA) did not reveal any hybridization. Considering the high connectivity of shipping and boating in Panama, Saccostrea sp. may have been introduced to the Caribbean by either recreational or commercial vessels, but the timing and potential ecological effects of this invasion remain unknown.