The evolution of robustness and fragility during long-term bacterial adaptation

Area of Science:

• Evolutionary biology
• Microbial genetics
• Population genetics

Background:

• Theory suggests adapted populations evolve mechanisms to counter deleterious mutations.
• Mutational robustness evolution during adaptation is debated, especially regarding pleiotropic effects.

Purpose of the Study:

• Investigate the spontaneous evolution of mutational robustness and pleiotropic effects during adaptation.
• Examine how adaptation in Escherichia coli affects mutation impacts over 15,000 generations.

Main Methods:

• Studied point mutations in RNA polymerase of Escherichia coli.
• Tracked adaptive trajectory over 15,000 generations.
• Assessed fitness effects of beneficial and deleterious mutations in adapted backgrounds.

Main Results:

• Fitness effects of mutations were attenuated in fitter Escherichia coli backgrounds.
• Pleiotropic effects of mutations became more severe and widespread with increased adaptation.
• Observed a trade-off between robustness and fragility in regulatory networks.

Conclusions:

• Adaptation can lead to increased mutational robustness but also greater pleiotropic effects.
• Evolutionary trade-offs between robustness and fragility can arise.
• Adaptation generates hidden variability with potential for unpredictable evolutionary consequences.