Genomic evidence for speciation with gene flow in broadcast spawning marine invertebrates

How early stages of speciation in free-spawning marine invertebrates proceeds is poorly understood. The Western Pacific abalones, Hatiois discus, H. madaka, and H. gigantea occur in sympatry with shared breeding season and are capable of producing viable F1 hybrids in spite of being ecologically differentiated. Population genomic analyses revealed that although the three species are genetically distinct, there is evidence for historical and ongoing gene flow among these species. Evidence from demographic modeling suggests that reproductive isolation among the three species started to build in allopatry and have proceeded with gene flow, possibly driven by ecological selection. We identified 27 differentiation islands between the closely related H. discus and H. madaka characterized by high FST and dA, but not high dXY values, as well as high genetic diversity in one H. madaka population. These genomic signatures suggest differentiation driven by recent ecological divergent selection in ...