Demographics of co-occurring species can often be diagnosed through population genomic analyses of single nucleotide polymorphisms (SNPs). These data can define population structure, gene flow, plus candidate regions in the genome that potentially reflect local adaptations. Importantly, they can gauge if populations are demographically open or closed (i.e., with global or local recruitment). We derived SNPs from double-digest restriction-site associated DNA (ddRAD) to test the demographics of

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... mmercially important queen conch (Lobatus gigas) and bonefish (Albula vulpes) from two northeast Caribbean Basin islands (Grand Bahama to the north and Eleuthera to the south). Specifically, we tested the hypothesis that the strong west-to-east current in the Great Bahama Canyon forms a vicariant barrier separating the two islands. We conducted Bayesian assignment tests conducted on putatively neutral (L. gigas=64,863; A. vulpes=36,206 SNPs) and highly-differentiated outlier SNP datasets (L. gigas=51 to 88; A. vulpes=79 to 123, respectively). For conch, both analyses indicated weak structure, substantiating the vicariant hypothesis. However, results for bonefish suggested adult mobility and strong easterly currents as potential drivers for source-sink dynamics. These results, while preliminary, provide templates for future research endeavors with these impacted species. Outlier loci, for example, can potentially place populations of each within a demographic continuum, rather than within a dichotomous open/closed framework, as well as diagnose source and sink populations, as herein. These methodologies can then be applied to codistributed species with similar but less well understood ecologies so as to evaluate basin-wide trends in connectivity and local adaptation.