Figure 2: Numerical simulation results for the epistatic trade-off model (Case 1). Various properties are shown as a function of the migration rate, expressed relative to the strength of ecological selection on the A locus, s. The migration rates numbered 1–12 correspond to ; migration is symmetric, that is, . The points in black represent values prior to the evolution of the modifier (i.e., assuming both populations fixed for the B allele as shown in Time 1 in Figure 1). Colored points represent values after the evolution of the modifier; different colors correspond to modifiers of varying effects (see legend). Left column: moderate linkage ; right column: no linkage: . (a) Divergence at A locus. (b) Divergence at B locus. (c) Intrinsic isolation as measured by the average fitness individuals from Populations 1 and 2 compared to the average fitness of hybrids. (d) Strength of the barrier into Population 1. (e) Strength of barrier into Population 2. Parameter values used: . See text for details.