South American homogeneity versus Caribbean heterogeneity: population genetic structure of the western Atlantic fiddler crab Uca rapax (Brachyura, Ocypodidae)

The majority of marine species, including fiddler crabs, are thought to be genetically homogeneous due to their planktonic larval stages. However, recent studies have uncovered genetically structured populations in other littoral crabs thriving in mangroves. To determine the population genetic structure of the widespread mudflat fiddler crab Uca rapax, Smith, 1870 along the western Atlantic and the Caribbean Sea, mitochondrial Cox 1 sequence data of seven populations were compared and analyzed. We computed a haplotype network, nucleotide and haplotype diversities and conducted an AMOVA. While the three mainland populations examined (Brazilian states of São Paulo and Pará; Suriname) are genetically indiscernible as expected, populations from four Caribbean islands (St. Martin, Hispaniola, Jamaica, Cuba) showed significantly restricted gene flow among each other as well as compared to the mainland populations. Our data suggest the absence of possible barriers to gene flow between mainland sites, whereas a hindrance to genetic exchange seems to be present between mainland and Caribbean islands as well as among the islands.