Fig. 6

The role of different fitness distributions on IS persistence. The mean cell proportion with ISs, the mean cell fitness and the mean IS copy were computed conditional on the persistence of ISs. Top: Transposition bursts with evolving regulation occur after 5000 generations; the magnitude of positive (a) and negative (d) selective forces are given in the horizontal axis and legends respectively. The persistence of ISs is significantly affected by the magnitude of beneficial selection, and an estimated threshold value of a=10^−4.07 (vertical dashed line) calculated based on Eq. 3 reasonably predicts when ISs would be lost. Bottom: There is no beneficial IS-induced mutation (p _a =0) during the first 5000 generations; transposition bursts with evolving regulation and increase in p _a occur thereafter except for the blue curve (no burst, δ=γ=0), corresponding values of p _d for each curve are provided in the legends. IS persistence is favoured by transposition bursts and more IS-induced adaptive mutations. Each pair of parameters was simulated for 1000 runs, and each simulation was run for 30,000 generations. The population is initialised with an IS distribution according to Sawyer et al. [62]. Other parameter values are as given in Table 1