Adaptation limits diversification of experimental bacterial populations

Area of Science:

• Evolutionary biology
• Microbial ecology
• Population genetics

Background:

• Theoretical models suggest that adaptation to a specific ecological niche can restrict a population's capacity for future diversification.
• Understanding this constraint is crucial for predicting evolutionary trajectories and biodiversity patterns.

Purpose of the Study:

• To experimentally test the theory that niche specialization imposes constraints on subsequent diversification.
• To investigate the evolutionary dynamics of niche specialists using a model organism.

Main Methods:

• Utilized laboratory microcosms with the bacterium Pseudomonas fluorescens, known for its diversification into niche specialists.
• Propagated numerically dominant genotypes in isolation to observe adaptation and diversification.
• Conducted subsequent experiments to rule out alternative explanations like niche generalism or reduced intrinsic evolvability.

Main Results:

• Populations of Pseudomonas fluorescens showed significant increases in fitness over time.
• Crucially, these adapted populations exhibited a markedly reduced ability to diversify into new niches.
• Niche generalists and reduced intrinsic evolvability were experimentally excluded as causes for the observed diversification constraint.

Conclusions:

• Niche specialization can impose a significant cost in terms of reduced potential for future diversification.
• This study provides empirical support for the theoretical constraints imposed by adaptation.
• Findings highlight a fundamental trade-off between optimizing for a current niche and maintaining the capacity for future adaptation.