Overview of the study system. During a 10-day evolution experiment, ancestral E. coli evolve under selection pressure by phage U136B. E. coli populations evolve phage resistance through either large-effect changes to TolC (blue, loss-of-function mutations that result in antibiotic sensitivity) or small-effect change to TolC (green, no loss-of-function). Meanwhile, the phage U136B populations also evolve new genotypes and phenotypes, investigated in this study.