Experimental adaptive radiation in Pseudomonas.

Area of Science:

• Evolutionary biology
• Microbial evolution
• Experimental evolution

Background:

• Adaptive radiation explains the diversification of species.
• Understanding the interplay between selection and constraint is crucial for evolutionary studies.

Purpose of the Study:

• To investigate the role of selection and constraint in adaptive radiation limits.
• To examine the consequences of adaptive radiation in an experimental system.

Main Methods:

• Propagated four replicate lines of Pseudomonas fluorescens in 95 environments for 1,000 generations.
• Assayed growth performance of evolved lines and ancestral clone in all environments.
• Analyzed direct and correlated responses to selection, including niche expansion and adaptation costs.

Main Results:

• Evolved lines improved performance in selection environments and invaded 70% of novel environments.
• Direct responses were larger in initially poor growth environments.
• Correlated responses were generally positive, leading to niche expansion and collective habitat occupation.
• Observed 'roundabout selection' where adaptation occurred via indirect environmental pressures.
• Mutation accumulation via neutral drift explained most adaptation costs.

Conclusions:

• Experimental evolution in Pseudomonas fluorescens demonstrates significant niche expansion beyond direct selection.
• Findings challenge classical niche evolution theories, highlighting the importance of correlated responses and roundabout selection.
• Neutral drift plays a key role in the generation of adaptation costs during evolutionary processes.