Answering Whether Evolutionary Outcomes Are Unique Through Parallel Adaptive Evolution Experiments

Abstract

Adaptive evolution experiments are employed in biotechnology and metabolic engineering to finetune a cell’s metabolism at the global level after introduction of heterologous pathways. Such an approach reaps benefits of expediency and has been experimentally proven in many studies. But, at the fundamental level, one may ask: is the evolutionary result unique? Specifically, would the same evolutionary outcome replay itself both at the macro-level (i.e., phenotype) and micro-level (i.e., mutational profile) upon repeat of the experiment? This question could be answered experimentally by conducting adaptive evolutionary experiment in parallel. Typically, adaptive evolution experiments are conducted through a single shake flask or bioreactor, and is time-consuming given the large amount of time needed for mutations beneficial to fitter phenotype to appear. However, if adaptive evolution experiments are ran in more shake flasks and bioreactors in parallel, one may have a higher chance to observe beneficial phenotypes in a shorter period of time based on chance events. More importantly, parallel adaptive evolution experiments provide greater opportunities to search the vast mutational space for beneficial genotypes that lead to desired phenotypes. But, at the deepest level, parallel adaptive evolution experiments afford us the tools to answer the fundamental question of whether each evolutionary trajectory taken is unique through whole-genome sequencing of the evolved strain. Answers to the question may fundamentally reshape our understanding of evolution, natural selection, and how organisms adapt to changing environment. In closing, each evolutionary trajectory taken is likely to be unique, but some trajectories could still share similar mutations at particular genomic spots given the tight coupling between phenotype benefit and mutations that growth processes in adaptive evolution experiment selects for. Specifically, only certain mutations would confer a fitness advantage to the organism, and natural selection through a fitter growth phenotype would select for this mutation to be entrenched in the evolved genetic repertoire.

Keywords: adaptive evolution, evolutionary trajectory, phenotype selection, growth-based selection, mutational profile,