Fig. 1

A speciation model involving the genome-hitchhiking[8] and the genome-wide congealing[10]. The X-axis is the number of loci that are targeted by divergent selection, and the y-axis is the level of overall genomic differentiation between two speciating populations (PopA and PopB). (i) Only a few targets are targeted by divergent selection. Selectively targeted loci are differentiated between PopA and PopB while the rest of the genome is undifferentiated by gene flow. (ii) A large number of loci are targeted by mild divergent selection and the combined effect of the mild selection effectively decreases the migration rate between PopA and PopB (the Genome-hitchhiking model). Then, genomic differentiation occurs while the level of differentiation is still low. (iii) The synergistic effect among linkage equilibriums at targets accelerates the rate of genomic differentiation in the presence of following divergent selection (the genome-wide congealing). (iv) Whole-genome sequences are completely differentiated, and the process of speciation is completed