Phenotypic evolution is of great significance within biology, as it is the culmination of the influence of key evolutionary factors on the expression of genotypes. Deeper studies of the fundamental components, such as fitness effects of mutations and genetic variance within a population, allow one to predict the evolutionary trajectory of phenotypic evolution. In this regard, how much the change in mutational variance and the ongoing natural selection influence the rate of phenotypic evolution has yet to be fully understood. Therefore, this study measured mutational variances and the increasing rate of genetic variance during the experimental evolution of Escherichia coli populations, focusing on two growth-related traits, the populational maximum growth rate and carrying capacity. Mutational variances were measured by mutation-accumulation experiments, which allowed for the analysis of the effects of spontaneous mutations on growth-related traits in the absence of selection. This analysis revealed that some evolved populations developed a higher mutational variance for growth-related traits. Further investigation showed that most evolved populations have also developed a greater mutational effect, which could explain the increase in mutational variance. Finally, the genetic variances for most evolved populations are lower than expected in the absence of selection, and the involvement of either stabilizing or directional selection is evident. Future experiments with a larger sample size of experimentally evolved populations, as well as more intermediate timepoints during experimental evolution, may provide further insight regarding the complexities of the evolutionary outcomes of these traits.

Different populations of evolved E.coli and their ancestors were grown in a variety of single amino acid environments to determine their ability to use that amino acid as a carbon source. Some evolved lines were able to grow in amino acids that their ancestors weren't able to. The source of this change in amino acid growth was investigated by testing uptake, searching for candidate mutations, and comparing growth rates of populations with and without certain mutations.

Mutation rate is the rate of appearance for mutations to occur in a living organism. Studying and quantifying mutation rates and their evolution is important because mutations are the ultimate source of genetic variation and one of the reasons why evolution occurs. Much of the current research has investigated the mutational rate increase. The evolution of reduced mutation rate, which can be favored by natural selection because the accumulation of too many mutations can be deleterious and result in death, is less studied. Therefore, this study will be focused on antimutators, which are mutations that result in a lowering of the mutation rate. Using Escherichia coli K-12 str. MG1655 as a model system, the effects and reasons for how MMR- background E. coli evolves lower mutation rates were studied. Here we show that the candidate antimutator in dnaE lowers the mutation rate in an experimentally evolved population of E. coli with MMR- background by using a mutation rate assay to demonstrate the difference between populations with and without the antimutator candidate. The results also suggest the importance of an antimutator for populational survival.

Phenotypic evolution is an essential topic within the general field of evolution. Theoretically, the outcome of phenotypic evolution may be influenced by factors such as genetic background and the interaction of natural selection and genetic drift. To gain empirical evidence for testing the effects of those factors, we used eight long-term evolved Escherichia coli populations as a model system. These populations differ in terms of genetic background (different mutation rates) as well as bottleneck size (small- and large-magnitude). Specifically, we used a plate reader to measure three growth-related traits: maximum growth rate (umax), carrying capacity (Kc), and lag time (Lt) for 40 clones within each population. For each trait we quantified the change in mean per generation, the change in variance per generation, and the correlation coefficient between pairs of traits. Interestingly, we found that the small and large bottleneck populations of one background displayed clear, distinguishing trends that were not present within the populations of the other background. This leads to the conclusion that the influence of selection and drift on a population’s phenotypic outcomes is itself influenced by the genetic background of that population. Additionally, we found a strong positive correlation between umax and Kc within each of the high-mutation populations that was not consistent with our neutral expectation. However, the other two pairs did not exhibit a similar pattern. Our results provide a novel understanding in the relationship between the evolution of E. coli growth-related phenotypes and the population-genetic environment.