Figure 2.

Distribution of the selection coefficient under Fisher’s model for various fitnesses of the ancestral strain W₀ (left: far from the optimum, right: near the optimum) and various complexities of the phenotypic space (from bottom to top). The line is the χ₂ analytical approximation (equation 2), the dashed line is based on the gamma approximation developed in Martin and Lenormand (2006) (Appendix) and the dotted line for W₀ = 0.9 is the beta approximation developed in Martin and Lenormand (2008). Selection coefficient is calculated for 10000 selected mutations. σ_mut is scaled such that the average norm of the mutational effect on phenotype is constant equal to 0.1 across complexities. The population size is N = 10⁷ and the mutation rate μ = 10⁻⁹.