Figure 6
From: How does epistasis influence the response to selection?
Comparison between quadratic and truncation selection on the deviation from a multitrait optimum. The left panel shows the distribution of distance from the optimum, r, for n=3, 10, 30, 100 traits (left to right), under quadratic stabilising selection; the upper curve shows the fitness, exp(−(S/2) r2). The right panel shows the same, but for truncation selection in which only individuals with r<2 reproduce. Simulations are of 100 haploid individuals, each with 100 unlinked loci; alleles have continuously distributed vectors of effects. The trait is the sum of effects of each locus. Mutation rate is 0.001 per locus, and adds a random Gaussian with s.d. σ=0.1 for each trait. Results are averaged over generations 4000 to 20 000. Under quadratic stabilising selection, the reduction in mean fitnesses is 0.014, 0.046, 0.127 and 0.318 for 3,…, 100 traits. In contrast, under truncation selection the loss of mean fitness (that is, the fraction of offspring with r>2) are 0.00247, 0.00642 and 0.0269 for 3, 10, 30 traits. With 100 traits under truncation selection, the population does not equilibrate: loci fix deleterious alleles, leading to a decline in fitness through Muller’s Ratchet.
