Fig. 4.
The distributions of shifted fitness effects for two viruses. The null hypothesis (H0: k = 0) is that the fitness distribution belongs to the Gumbel domain of attraction. The alternative hypothesis (HA: k ≠ 0) is that the distribution is in either the Weibull (k < 0) or Fréchet (k > 0) domain. The dashed and solid lines depict the fitted densities under the null and alternative models respectively. p-values are based on 10,000 parametric bootstrap replicates. The shifted empirical fitnesses, plotted as vertical lines, are compared to their expected values under the fitted null (vertical lines with k = 0) and alternative (vertical lines with k = −1) models. (a) The nine beneficial mutations for the DNA phage ID11. (b) The 16 host range mutations for RNA phage ϕ6