Survival probability as a function of mutation rate, for four different models of deleterious fitness effects.

<p>In all cases the model follows the broad scheme laid out in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068179#pone-0068179-g001" target="_blank">Figure 1</a>, with an initial strain (reproductive number <i>R</i>₁) and a fitter strain () both threatened by deleterious mutations. Solid lines: our general model with lethal sites; if one of these sites is mutated, . Dashed lines: fitness is if one of the deleterious sites is mutated, and <i>R</i>₀ = 0 (lethal) if deleterious sites are mutated. Dotted lines: fitness is if any (non-zero) number of deleterious sites is mutated. Dot-dashed lines: fitness is , with dependent on the allele at the adaptive site and the number of mutated deleterious sites. , , , . Numeric results using equations detailed in appendix S4 in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0068179#pone.0068179.s001" target="_blank">file S1</a>.