Antibiotic concentrations vary dramatically in the body and the environment. Hence, understanding the dynamics of resistance evolution along antibiotic concentration gradients is critical for predicting and slowing the emergence and spread of resistance. While it has been shown that increasing the concentration of an antibiotic slows resistance evolution, how adaptation to one antibiotic concentration correlates with fitness at other points along the gradient has not received much attention. Here, we selected populations of Escherichia coli at several points along a concentration gradient for three different antibiotics, asking how rapidly resistance evolved and whether populations became specialized to the antibiotic concentration they were selected on. Populations selected at higher concentrations evolved resistance more slowly but exhibited equal or higher fitness across the whole gradient. Populations selected at lower concentrations evolved resistance rapidly, but overall fitness in the presence of antibiotics was lower. However, these populations readily adapted to higher concentrations upon subsequent selection. Our results indicate that resistance management strategies must account not only for the rates of resistance evolution but also for the fitness of evolved strains.

The dataset consists of: a) experimental evolution data tracking the development of resistance to three antibiotics in replicate E.coli populations. This dataset consists of OD600 measurements taken on each daily transfer. b) fitness assays as growth curve measurements of each evolved population measured in the presence and absence of antibiotics. The uploaded code is the R code used by statistical analyses.

Funding provided by: Wellcome TrustCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010269Award Number: 216779/Z/19/Z