Fig 2. Hybrid populations rapidly fix for hybrid incompatibility locus pairs.

Selection drives hybrid incompatibility loci to fixation, even when a hybrid population forms at equal admixture proportions (f = 0.5). Black lines show average parent 1 ancestry at a hybrid incompatibility pair (h = 0.5, s = 0.1) in 50 replicate populations of (A) N = 1,000 or (B) N = 10,000 diploid individuals. Gray lines show results for this same population size with no selection. Because of this behavior, two incompatibility pairs may fix for opposite parents, resulting in reproductive isolation of hybrids from both parents (see Fig. 1).