Ecological Adaptation and Speciation: The Evolutionary Significance of Habitat Avoidance as a Postzygotic Reproductive Barrier to Gene Flow

Figure 3

Illustration of model 3 based on epistasis between ancestral and novel habitat loci with preference and avoidance alleles. Numbered steps of model (1–4) are separated by dashed lines and ordered vertically. Individuals are represented by chromosome pairs as grey bars; ancestral (on left) and novel (on right) habitat loci are marked by two pairs of vertical black tick marks on grey chromosomes. Alleles at ancestral locus are labeled as follows: 𝑎⁺: preference for ancestral habitat; 𝑎⁻: avoidance for ancestral habitat. Alleles at novel locus are labeled as follows: 𝑛⁺: preference for novel habitat; 𝑛⁻: avoidance for novel habitat. Arrow depicts shift from ancestral habitat 1 to novel habitat 2.