Figure 2.

The influence of the dominance function of a plasmid mutation and of gene dosage effects on the establishment of resistance-conferring plasmid variants and the probability of evolutionary rescue. We consider three generic types of dominance functions for plasmid mutations (i–iii) and gene dosage effects (iv). (A–D) Illustration of the relation between cell types and their Malthusian fitness. (E–H) Establishment probabilities of a plasmid mutation arising on a single plasmid copy. (I–L) Probability of evolutionary rescue from de novo mutations. Without gene dosage effects, the establishment probability decreases with the plasmid copy number. Yet, the probability of evolutionary rescue may still increase with n if the decline in the establishment probability is compensated by the increased mutational supply. Results for the establishment probabilities were obtained numerically by using Equation (A.5) with Equation (A.1). These were inserted into Equation (3) to obtain the probability of evolutionary rescue. Parameters: s₀ = −0.1, $u\overline{N}=0.1,$ $\overline{N}={10}^5.$ Open circles show averages over 10⁴ stochastic simulations. Error bars indicate twofold SE.