Figure 2.

The effects of migration rate and relative fitnesses on mutation-order divergence when the novel alleles arise at different loci (epistasis model). Squares with continuous line show the frequency of allele A in patch 1 (P₁); circles with dashed lines show the frequency of allele A in patch 2 (P₂). In panels (a,b), the mutations (alleles A and B) arise simultaneously. In panels (c–l), allele B reaches a frequency q_thresh in at least one patch before allele A arises in patch 2. In all panels, there is no allopatric divergence period (i.e. t_contact = 0). Strong population divergence (i.e. p₁ ≈ 0 and p₂ ≈ 1) via the mutation-order process occurs when there is no migration (all panels) or when the migration rate is low and fitnesses are relatively similar (right-hand panels). Note that while the frequencies of allele B are not shown, by the end of a simulation, we have q_i ≈ 1 − p_i (i.e. either A or B becomes common in a patch by the end).