Figure 6 .

Fitness surface and ESS ridges in the two-locus model with competitive allocation (u = 1). Parameters are α_A = 1/4, α_B = 1/2 with β₁ = β₂ = 1/2 in A and C and β₁ = 0.2, β₂ = 0.8 in B and D. Trait fitness is robust (v = 1/2) in A and B and sensitive (v = 2) in C and D. The ridge is presented as a solid line, using Equation A10 when β₁ = β₂ or determined numerically otherwise. Darker colors represent lower fitness values. The ESS ridge is attracting in A and B and favors the evolution of some degree of pleiotropy at both genes, while specialist strategies are favored in C and D, with both genes specialized on the same trait, denoted by the circles and the arrows pointing away from the ridge.