Theoretical Expression for the Evolution of Genomic Island of Speciation: From Its Birth to Preservation

Ecological speciation could be driven by divergent selection that works to maintain phenotypes that are adaptive to each niche. In its early stages, genetic divergence (or F ST ) can be maintained around the target sites of divergent selection, while in other regions, genetic variation can be mixed by gene flow or migration. Such regions of elevated genetic divergence are called genomic islands of speciation. In this work, we theoretically consider the evolutionary process of a genomic island of speciation, from its birth to stable preservation. Under a simple two-population model, we use a diffusion approach to obtain analytical expressions for the probability of initial establishment of a locally adaptive allele, the reduction of genetic variation due to the spread of the adaptive allele, and the process to the development of a sharp peak of divergence. Our result would be useful to understand how genomes evolve through ecological speciation with gene flow.