Accuracy of the analytic approximation for weak to moderate selection. Percentage of error, calculated as (Papprox − Pexact)/(Pexact − PC), is plotted as a function of the strength of selection (s) for five types of hybrid incompatibility: autosome–autosome (A–A), autosome–X (A–X), autosome–Y (A–Y), X–X, and X–Y. Exact values were obtained from four-locus simulations. The strengths of migration (m), natural selection on the male trait (sT), and sexual selection (α) were varied as a function of s, where m = s/80, sT = s, α = 2s. The strength of selection on hybrid incompatibility also varied as a function of s, where s00 = 0, s11 = s/4, s01 = s10 = s12 = s21 = s/2, s02 = s20 = s.