Fig. 2: Competition between populations may prevent runaway plasmid invasion.

A Illustration of multiple populations, each occupying an isolated “deme”. During each epoch, populations compete for demes, with plasmid invasion occurring randomly (see Eq. 11 for details). In the example shown, in the first epoch, the population with two plasmids is replaced by the population with zero plasmids. In the second epoch, the population with magenta plasmids is invaded by the green plasmid. B Multiplasmid fitness costs for different types of epistasis. With no epistasis, fitness burden is multiplicative as in Fig. 1F. With positive epistasis, fitness burden increases sub-multiplicatively (pictured: \({\Delta}_{{\mathrm{tot}}} \,=\, {\Delta}\) for \(m \,> \, 0\)). For negative epistasis, fitness burden increases super-multiplicatively (pictured: \({\Delta}_{{\mathrm{tot}}} \,=\, 1 \,-\, (1 \,-\, {\Delta})^{m^{3/2}}\)). C Steady-state distributions of number of plasmid types per cell in the Wright–Fisher model (see SI Appendix 3). Parameters \({\Delta} \,=\, 0.01\) and plasmid invasion probability for each time period \(q \,=\, 0.005\).