Parallel genetic adaptation across environments differing in mode of growth or resource availability

Area of Science:

• Evolutionary Biology
• Microbial Evolution
• Genetics

Background:

• Experimental evolution studies show high genetic parallelism in identical environments.
• Natural populations face complex, variable environments, sharing some but not all characteristics.
• Understanding shared selection pressures in distinct environments is crucial for evolutionary insights.

Purpose of the Study:

• To investigate whether shared selection pressures drive parallel evolution across distinct environments.
• To determine the extent of genetic similarity between bacterial populations evolved under varying conditions.
• To assess the correlation between genetic parallelism and environmental fitness.

Main Methods:

• Experimentally evolved populations of *Burkholderia cenocepacia* over 90 days (approx. 600 generations).
• Populations evolved under all combinations of high/low carbon availability and planktonic/biofilm growth selection.
• Genetic similarity and fitness were measured across different evolved populations and environments.

Main Results:

• Populations sharing selection pressures (carbon availability or growth mode) showed higher genetic similarity.
• Not all shared pressures resulted in parallelism; low-carbon environments showed low parallelism between biofilm and planktonic growth.
• Fitness in a specific environment positively correlated with genetic similarity to populations evolved in that environment.

Conclusions:

• Shared selection pressures generally promote genetic parallelism, but environmental trade-offs can limit this.
• Evolution in similar environments leads to increased genetic parallelism, which is linked to enhanced fitness.
• This study highlights the nuanced relationship between environmental factors, genetic adaptation, and evolutionary outcomes.