Experimental evidence that network topology can accelerate the spread of beneficial mutations

Whether and how the spatial arrangement of a population influences adaptive evolution has puzzled evolutionary biologists. Theoretical models make conflicting predictions about the probability a beneficial mutation will become fixed in a population for certain topologies like stars, in which “leaf” populations are connected through a central “hub.” To date, these predictions have not been evaluated under realistic experimental conditions. Here, we test the prediction that topology can change the dynamics of fixation both in vitro and in silico by tracking the frequency of a beneficial mutant under positive selection as it spreads through networks of different topologies. Our results provide empirical support that metapopulation topology can increase the likelihood that a beneficial mutation spreads, broadens the conditions under which this phenomenon is thought to occur, and points the way towards using network topology to amplify the effects of weakly favored mutations under directed evolution in industrial applications. 

Methods
This data was collected from experimentally evolving laboratory populations of P. aeruginosa strain 14 (PA14) under a sub-inhibitory concentration of Ciprofloxacin and a novel agent-based SANCTUM model. The raw counts and proportions of the mutant bacteria PA14-gyrA wild-type non-mutant PA14-LacZ are both available. The proportions have been used to perform all the statistical analyses.