Fig. 3.

Frequency-resolved LD between deleterious mutations as a function of the scaled fitness cost of the double mutant. Top: the signed LD moment, ${\sigma }_d^1(f_0)$, in Equation (7) is depicted for pairs of nonrecombining loci with additive (ϵ = 0), antagonistic (ϵ$<0$), and synergistic (ϵ$>0$) epistasis, which were chosen to have the same total cost for the double mutant ($s_{AB}=s$). Symbols denote the results of forward-time simulations (Appendix A) across a range of parameters with $s>10/N$, and each symbol is colored by the corresponding value of f₀. The solid lines shows the theoretical prediction from Equation (C8). Bottom: an analogous figure for the squared LD moment, ${\sigma }_d^2(f_0)$, where solid lines show the theoretical predictions from Equation (C9). The “data collapse” in both panels indicates that frequency-weighted LD is primarily determined by the compound parameters $Ns{f}_0$ and Nϵf₀. Weak scaled fitness costs ($Ns{f}_0\lesssim 1$) lead to an excess of coupling linkage (${\sigma }_d^1>0$), which qualitatively resembles the effects of antagonistic epistasis (ϵ$<0$).