Ecological effects on mutation rate

  • Guillaume Gomez

Student thesis: Phd


Mutation is key to an organism's evolution. By producing variation among genomes, it brings the variation into populations required for natural selection to act. The rates at which these mutations arise therefore affect the organism's adaptation and evolution. Because the majority of mutations are neutral or deleterious, one might expect mutation rates to be minimised. In a wide range of species across domains of life, mutation rates are inversely associated with the effective population size, which determines the balance between the forces of selection and genetic drift. However, within an organism these mutation rates have not evolved to a constant minimum, but instead vary depending upon the environment. Specifically, an inverse association between mutation rate and population density has been identified in several organisms. Through this thesis, I address the questions of the evolution of mutation rates and the environmentally associated mutation rate plasticity, testing the underlying mechanisms involved. In the first experimental chapter, I simulate ecological effects on mutation rate evolution and find that evolvable mutation rates converge to different optimal values according to the environmental conditions, enabling increased fitness in both short and long-term time scales relative to fixed mutation rates. I then investigate empirically in the second experimental chapter the density associated mutation rate plasticity (DAMP), finding that it is present at multiple marker loci giving resistance to antibiotics cycloserine and rifampicin, specifically cycA and rpoB, in the genome of Escherichia coli. By testing this relationship with deletion mutants for genes involved in the putrescine degradation pathway, I show that several of them affect mutation rate in both directions at the rpoB locus. In the final experimental chapter, I investigate DAMP in continuous cultures, aiming to disentangle growth-related effects. I demonstrate that growth rate, nutrient supply and population density, while partially confounded in batch cultures, have separable effects on mutation rates at both the cycA and rpoB loci, with the glucose concentration affecting the degree of DAMP. These results support the prevalence of DAMP in micro-organisms as a highly evolved ecological trait and contribute to the understanding of how ecological effects can affect the course of evolution through their influence on mutation rates.
Date of Award31 Dec 2021
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorAndrew Mcbain (Supervisor), Daniela Delneri (Supervisor) & Chris Knight (Supervisor)


  • Individual-based model
  • Stress-induced mutagenesis
  • Chemostat
  • Evolvability
  • Fluctuation test

Cite this