Como na fábula de Esopo, quem evolui lenta e gradualmente ao longo das eras, evolui melhor

sexta-feira, março 18, 2011

Slow evolvers win in the end

Joseph Milton

In bacterial populations, speed kills. In Aesop's fable about the tortoise's victory over the hare, a slow, steady approach trumps a fast and impulsive one. And when it comes to evolution — for bacteria, at any rate — a leisurely pace may also be the best strategy for long-term survival.

Research carried out in Richard Lenski's lab at Michigan State University in East Lansing, and published today in Science 1, shows that rapidly evolving 'hare' bacteria were eventually wiped out by their more sluggish rivals.

The reason was that the 'tortoise' bacteria had a higher 'evolvability', or a greater potential to take advantage of future beneficial mutations, than their speedier competitors, despite a tendency to accumulate such mutations at a slower rate.
Science 18 March 2011: 
Vol. 331 no. 6023 pp. 1433-1436 
DOI: 10.1126/science.1198914


Second-Order Selection for Evolvability in a Large Escherichia coliPopulation

Robert J. Woods1,*†, Jeffrey E. Barrick2,*‡¶, Tim F. Cooper3, Utpala Shrestha3, Mark R. Kauth2, and Richard E. Lenski1,2,¶

+Author Affiliations

1Department of Zoology, Michigan State University, East Lansing, MI 48824, USA.
2Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA.
3Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, USA.

+Author Notes

↵† Present address: Department of Internal Medicine, University of Michigan, Ann Arbor, MI 48109, USA.

↵‡ Present address: Department of Chemistry and Biochemistry, Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, TX 78712, USA

¶To whom correspondence should be addressed. E-mail: (J.E.B.); (R.E.L.)

↵* These authors contributed equally to this work.


In theory, competition between asexual lineages can lead to second-order selection for greater evolutionary potential. To test this hypothesis, we revived a frozen population of Escherichia coli from a long-term evolution experiment and compared the fitness and ultimate fates of four genetically distinct clones. Surprisingly, two clones with beneficial mutations that would eventually take over the population had significantly lower competitive fitness than two clones with mutations that later went extinct. By replaying evolution many times from these clones, we showed that the eventual winners likely prevailed because they had greater potential for further adaptation. Genetic interactions that reduce the benefit of certain regulatory mutations in the eventual losers appear to explain, at least in part, why they were outcompeted.

Received for publication 12 October 2010.
Accepted for publication 1 February 2011.


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