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Updated: Mar 1, 2026
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Daily Transfers, Archiving Populations, and Measuring Fitness in the Long-Term Evolution Experiment with Escherichia coli
Published on: August 18, 2023
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EVOLUTIONARY ADAPTATION TO TEMPERATURE. VI. PHENOTYPIC ACCLIMATION AND ITS EVOLUTION IN ESCHERICHIA COLI
Albert F Bennett1, Richard E Lenski2
1Department of Ecology and Evolutionary Biology, University of California, Irvine, California, 92697.
Summary
The beneficial acclimation hypothesis, suggesting acclimation improves function in new environments, was largely rejected. Acclimation to a bacterium's evolutionary temperature, however, often enhanced fitness across various thermal conditions.
Area of Science:
- Microbiology
- Evolutionary Biology
- Physiology
Background:
- Acclimation involves reversible, nongenetic phenotypic changes induced by environmental conditions.
- The beneficial acclimation hypothesis posits that acclimation enhances function in the inducing environment.
Purpose of the Study:
- To experimentally test the beneficial acclimation hypothesis in the bacterium Escherichia coli.
- To measure the relative fitness of E. coli acclimated to different thermal environments.
Main Methods:
- Experimental manipulation of thermal environments for acclimation.
- Measurement of relative fitness of Escherichia coli populations under varying thermal conditions.
- Comparison of fitness between bacteria acclimated to different temperatures and their evolutionary temperatures.
Main Results:
- The beneficial acclimation hypothesis was supported in only 7 of 12 comparisons.
- In several instances, acclimation to the competition temperature did not improve fitness, or even decreased it.
- Acclimation to the bacterium's evolutionary temperature frequently enhanced fitness, even at non-evolutionary temperatures.
Conclusions:
- The beneficial acclimation hypothesis is not a universally applicable prediction for phenotypic adjustments.
- Acclimation to an organism's historical evolutionary temperature can confer a fitness advantage across multiple environments.
- Evolutionary history plays a crucial role in determining the adaptive value of acclimation.
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