Figure 4.

Epistatic fitness landscapes can produce dynamics that differ from all non-epistatic landscapes. (A) We consider two-site landscapes with genotypes ab, Ab, aB, and AB, with the population initially fixed for ab. Assigning Ab and aB equal fitnesses, we let C₁ be the selection coefficient of Ab and aB relative to ab and let C₂ be the selection coefficient of AB relative to Ab and aB. We set the mutation rates to be μ_l = ν_l = 1 for both sites. (B) Properties of two-site fitness landscapes using the parameterization described in the previous panel. The dark gray region shows the set of landscapes whose variance trajectories are convex at t = 0. The light gray region shows the set of landscapes whose equilibrium substitution rates are greater than twice their initial substitution rates. The diagonal dashed line with positive slope shows the set of non-epistatic fitness landscapes, whereas the diagonal dashed line with negative slope shows the set of epistatic landscapes whose fitness dynamics cannot be distinguished from the non-epistatic case.