Adaptation, Clonal Interference, and Frequency-Dependent Interactions in a Long-Term Evolution Experiment with...

Area of Science:

• Evolutionary biology
• Microbial evolution
• Population genetics

Background:

• Long-term experimental evolution provides insights into microbial adaptation.
• Understanding the genetic basis of adaptation requires tracking mutations over time.

Purpose of the Study:

• To reconstruct the genotypic evolution of an Escherichia coli population over 20,000 generations.
• To investigate the roles of selective sweeps, clonal interference, and frequency dependence in adaptation.

Main Methods:

• Analysis of whole-population samples of Escherichia coli (Ara-1) frozen every 500 generations.
• Tracking of 42 known mutations to reconstruct genotypic evolutionary history.

Main Results:

• Observed strong evidence of selective sweeps and clonal interference between competing lineages.
• Identified instances of simultaneous mutation fixation (mutational cohorts).
• Documented coexistence of two genetically diverged clades for over 6000 generations due to frequency-dependent interactions that eventually collapsed.

Conclusions:

• Clonal interference and frequency dependence are significant drivers of evolution even in simple microbial populations.
• Frequency dependence can prolong lineage coexistence beyond what clonal interference alone would sustain.
• Complex evolutionary dynamics, including clade coexistence and competitive exclusion, are shaped by interactions and accumulating beneficial mutations.