I am an evolutionary biologist who uses bacteria to study fundamental questions regarding the maintenance of organismal traits under relaxed selection, and the evolutionary potential of these traits once selection is introduced. Specifically, I focus on the evolution of antibiotic resistance because of its profound relevance to public health.
Maintenance and evolutionary potential of antibiotic resistance traits
A population may encounter an environmental change that removes or reduces a selective pressure that was previously important for the maintenance of a trait. Adaptation to the new environment can therefore affect an organism’s fitness in its prior environment. These correlated responses may lead to the functional decay of unused traits over time. In most cases, the evolutionary processes driving these responses are hard to disentangle because one must rely on retrospective studies and historical inferences.
Bacteria have large population sizes, fast generation times, and they are amenable to freezing and revival. One can therefore observe evolution in action, directly compare ancestral and evolved forms, and simultaneously assess adaptation in one environment and correlated fitness responses in another. In our research, we use the long-term evolution experiment (LTEE) with Escherichia coli to examine correlated responses. Briefly, 12 replicate populations were founded from a single common ancestor. These populations have been independently evolving for 30 years and over 60,000 generations in a medium without antibiotics. We therefore address how a prolonged period of relaxed selection affects the maintenance of antibiotic resistance traits, and the potential of LTEE strains to evolve increased resistance when drugs are introduced.
Genetic basis for constraint on antibiotic resistance evolution in an LTEE population
LTEE ancestral and evolved generation 50,000 strains gain resistance in the presence of antibiotics. Although one evolved strain has significantly lower evolvability compared to its common ancestor. My undergraduate mentee Jasper Gomez is determining the genetic basis underlying this observed constraint by examining how resistance evolvability changed during this population's evolutionary history.