Mutational robustness changes during long-term adaptation in laboratory budding yeast populations

Area of Science:

• Evolutionary Biology
• Genetics
• Molecular Biology

Background:

• Populations adapt by traversing fitness landscapes, where accumulated mutations can alter the landscape's local neighborhood.
• Changes in the distribution of fitness effects (DFE) can influence adaptation rates and the accumulation of deleterious mutations.
• Empirical data on DFE changes during evolution is scarce, despite numerous theoretical models.

Purpose of the Study:

• To empirically measure how the fitness landscape neighborhood changes during laboratory evolution.
• To investigate the impact of accumulated mutations on the DFE.
• To understand the role of epistasis in shaping the DFE during adaptation.

Main Methods:

• Utilized a barcode-based mutagenesis system to introduce specific gene disruptions.
• Measured the fitness effects of 91 gene disruptions in evolved strains.
• Compared evolved strains (8000-10,000 generations) in two constant environments.

Main Results:

• The mean of the DFE decreased in one environment, signifying reduced mutational robustness.
• The mean of the DFE remained unchanged in the second environment.
• Observed differences in DFE patterns were attributed to varying frequencies of epistasis, including fitness-correlated and idiosyncratic epistasis.

Conclusions:

• Laboratory evolution can dynamically alter the fitness landscape neighborhood.
• Changes in mutational robustness are environment-dependent and linked to epistasis.
• Epistatic interactions play a crucial role in shaping the DFE during adaptation.