Figure 1. Basic model structures.

Scenario A: The island population initially consists of individuals of genotype A_i A_i B_i B_i, whereas the mainland is homogeneous for genotype A_mA_mB_mB_m. Local selection acts on allele A_i on the island. After secondary contact is restored, genetic incompatibilities can occur between A_i and B_m. The model is extended by including Wolbachia in scenarios B–D. Colors indicate uninfected (white) and Wolbachia-infected populations (yellow and blue). Scenario B: Island infected with Wolbachia and mainland uninfected. Scenario C: Mainland infected with Wolbachia and no infection on the island before secondary contact. Scenario D: Before secondary contact, the island is infected with Wolbachia strain W_i and the mainland population with strain W_m. Scenarios B and C involve unidirectional CI, whereas scenario D involves bidirectional CI. After secondary contact, both nuclear and Wolbachia-induced cytoplasmic incompatibilities reduce number of offspring in intergroup matings.