Genetic structure and connectivity patterns of two Caribbean rocky-intertidal gastropods

The extent of gene flow in Caribbean marine communities has been investigated primarily in taxa from coral reef habitats, particularly in corals and reef fishes. Results from empirical population genetic studies in those taxa have indicated the presence of an east –west genetic break between 678 and 708W longitude, and isolation of populations in the Bahamas. Hydrodynamic modelling has further suggested the presence of four connectivity regions that may contribute to genetic isolation. In this study we test for the presence of genetic structure in two gastropods (Cenchritis muricatus and Echinolittorina ziczac) from poorly sampled rocky intertidal habitats, using mitochondrial sequence data. Significant genetic structure was found in C. muricatus (Snn ¼ 0.29, P , 0.001; Fst ¼ 0.022, P , 0.001), but not in E. ziczac (Snn ¼ 0.17, P ¼ 0.48; Fst ¼ 0.022, P ¼ 0.48), in spite of similar larval life histories. The pattern of differentiation does not match a simple east– west model in either species, nor a four-region model, nor do the Bahamas show evidence of isolation. However, the genetic differentiation of Bonaire from other sites that is observed in C. muricatus and E. ziczac is consistent with the previously observed isolation of this location in the trochid gastropod Cittarium pica.