How Organisms Can Tolerate Mutations, Yet Adapt to Environmental Change
ScienceDaily (Jan. 25, 2010) — Biologists at the University of Pennsylvania studying the processes of evolution appear to have resolved a longstanding conundrum: How can organisms be robust against the effects of mutations yet simultaneously adaptable when the environment changes?
A pea growing over two weeks. New research suggests that an optimal level of robustness maintains the phenotype in one environment but also allows adaptation to environmental change. (Credit: iStockphoto/Lachlan Currie)
Using an original mathematical model, researchers demonstrated that mutational robustness can either impede or facilitate adaptation depending on the population size, the mutation rate and a measure of the reproductive capabilities of a variety of genotypes, called the fitness landscape. The results provide a quantitative understanding of the relationship between robustness and evolvability, clarify a significant ambiguity in evolutionary theory and should help illuminate outstanding problems in molecular and experimental evolution, evolutionary development and protein engineering.
The key insight behind this counterintuitive finding is that neutral mutations can set the stage for future, beneficial adaptation. Specifically, researchers found that more robust populations are faster to adapt when the effects of neutral and beneficial mutations are intertwined. Neutral mutations do not impact the phenotype, but they may influence the effects of subsequent mutations in beneficial ways.
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Nature 463, 353-355 (21 January 2010) | doi:10.1038/nature08694; Received 4 November 2009; Accepted 19 November 2009
Jeremy A. Draghi1, Todd L. Parsons1, Günter P. Wagner3 & Joshua B. Plotkin1,2
Department of Biology,
Program in Applied Mathematics and Computational Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut 06520, USA
Correspondence to: Joshua B. Plotkin1,2 Correspondence and requests for materials should be addressed to J.B.P. (Email: jplotkin@sas.upenn.edu).
Abstract
Robustness seems to be the opposite of evolvability. If phenotypes are robust against mutation, we might expect that a population will have difficulty adapting to an environmental change, as several studies have suggested1, 2, 3, 4. However, other studies contend that robust organisms are more adaptable5,6, 7, 8. A quantitative understanding of the relationship between robustness and evolvability will help resolve these conflicting reports and will clarify outstanding problems in molecular and experimental evolution, evolutionary developmental biology and protein engineering. Here we demonstrate, using a general population genetics model, that mutational robustness can either impede or facilitate adaptation, depending on the population size, the mutation rate and the structure of the fitness landscape. In particular, neutral diversity in a robust population can accelerate adaptation as long as the number of phenotypes accessible to an individual by mutation is smaller than the total number of phenotypes in the fitness landscape. These results provide a quantitative resolution to a significant ambiguity in evolutionary theory.
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