Compensatory adaptation and diversification subsequent to evolutionary rescue in a model adaptive radiation

Area of Science:

• Evolutionary biology
• Microbial ecology

Background:

• Biological populations can survive environmental stress via evolutionary rescue.
• Rescued populations often exhibit reduced growth and genetic diversity.

Purpose of the Study:

• To investigate the recovery of population size and genetic diversity through compensatory evolution.
• To understand the relationship between population size, diversity, and growth performance during recovery.

Main Methods:

• Experimental evolution using the bacterium *Pseudomonas fluorescens*.
• Exposure to antibiotic stress followed by a one-individual population bottleneck.
• Monitoring population size and genetic diversity during compensatory evolution.

Main Results:

• Population size rapidly increased and stabilized during compensatory evolution.
• Genetic diversity increased at a slower pace and persisted longer than population size.
• Early compensatory evolution showed a positive correlation between population size and diversification, which diminished later.
• Final population size and diversity were independent of initial growth performance.

Conclusions:

• Compensatory evolution can restore population size and genetic diversity after severe stress.
• The dynamics of recovery are complex, with distinct phases for population size and diversity.
• A "holey" fitness landscape may explain the observed evolutionary patterns under antibiotic stress.