Figure 1.

Theoretical scheme of reinforcement speciation. Shown are 3 “island” populations and an ancestral scenario of divergence. The model assumes an ancestral population allopatrically splitting into 2 “subspecies” (subspecies 1 in island 1 and subspecies 2 in islands 2 and 3) that diverged in fitness-related loci. The second subspecies is split into 2 distinct island populations, a population that directly exchanges migrants with subspecies 1 (“sympatric population” in island 2) and a population that is not directly connected to subspecies 1 (“allopatric population” in island 3). Migration rate between subspecies 1 and 2 (m_ssp1-2) and between sympatric and allopatric populations of subspecies 2 (m_sym.-allo.) are independent and can be symmetrical or asymmetrical between each pair of interacting populations (see text). Shown are ancestral genotype and subsequent substitutions at A-D loci as well as introduced mutations at these loci upon simulation (indicated by astericks). Two different ecological scenarios are explored depending on whether sympatric and allopatric populations of subspecies 2 occupy the same (“Ecological Scenario 1”) or different (“Ecological Scenario 2”) environments (see section “Model”).