Fisher's geometrical model and the mutational patterns of antibiotic resistance across dose gradients.
Fisher's geometrical model (FGM) has been widely used to depict the fitness effects of mutations. It is a general model with few underlying assumptions that gives a large and comprehensive view of adaptive processes. It is thus attractive in several situations, for example adaptation to antibiotics, but comes with limitations, so that more mechanistic approaches are often preferred to interpret experimental data. It might be possible however to extend FGM assumptions to better account for mutational data. This is theoretically challenging in the context of antibiotic resistance because resistance mutations are assumed to be rare. In this article, we show with Escherichia coli how the fitness effects of resistance mutations screened at different doses of nalidixic acid vary across a dose-gradient. We found experimental patterns qualitatively consistent with the basic FGM (rate of resistance across doses, gamma distributed costs) but also unexpected patterns such as a decreasing mean cost of resistance with increasing screen dose. We show how different extensions involving mutational modules and variations in trait covariance across environments, can be discriminated based on these data. Overall, simple extensions of the FGM accounted well for complex mutational effects of resistance mutations across antibiotic doses.
UMR 5175 CEFE, CNRS-Université Montpellier-Université P. Valéry-EPHE, Montpellier Cedex 5, France.
Noémie
N
Harmand
INRA-UMR BGPI, Cirad TA A-54/K Campus International de Baillarguet 34398 Montpellier Cedex 5, France.
Romain
R
Gallet
UMR 5175 CEFE, CNRS-Université Montpellier-Université P. Valéry-EPHE, Montpellier Cedex 5, France.
Roula
R
Jabbour-Zahab
Institut des Sciences de l'Evolution de Montpellier, UMR CNRS-UM II 5554, Université Montpellier II, 34 095 Montpellier cedex 5, France.
Guillaume
G
Martin
UMR 5175 CEFE, CNRS-Université Montpellier-Université P. Valéry-EPHE, Montpellier Cedex 5, France.
Thomas
T
Lenormand
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics*; D019143:Evolution, Molecular; D008957:Models, Genetic; D009154:Mutation; D012641:Selection, Genetic
D000900:Anti-Bacterial Agents
E. coli; adaptation; fitness cost; fitness landscape; trade-offs