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The genetics of adaptation for eight microvirid bacteriophages.

Rokyta DR, Abdo Z, Wichman HA - J. Mol. Evol. (2009)

Bottom Line: Despite this, final fitnesses did not vary significantly among replicates.A positive correlation was found between the number of substitutions in an adaptive walk and the magnitude of fitness improvement, but no correlation was found between starting and ending fitness.These results provide an empirical framework for future adaptation theory.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Idaho, Moscow, ID 83844-3051, USA.

ABSTRACT
Theories of adaptive molecular evolution have recently experienced significant expansion, and their predictions and assumptions have begun to be subjected to rigorous empirical testing. However, these theories focus largely on predicting the first event in adaptive evolution, the fixation of a single beneficial mutation. To address long-term adaptation it is necessary to include new assumptions, but empirical data are needed for guidance. To empirically characterize the general properties of adaptive walks, eight recently isolated relatives of the single-stranded DNA (ssDNA) bacteriophage phiX174 (family Microviridae) were adapted to identical selective conditions. Three of the eight genotypes were adapted in replicate, for a total of 11 adaptive walks. We measured fitness improvement and identified the genetic changes underlying the observed adaptation. Nearly all phages were evolvable; nine of the 11 lineages showed a significant increase in fitness. However, fitness plateaued quickly, and adaptation was achieved through only three substitutions on average. Parallel evolution was rampant, both across replicates of the same genotype as well as across different genotypes, yet adaptation of replicates never proceeded through the exact same set of mutations. Despite this, final fitnesses did not vary significantly among replicates. Final fitnesses did vary significantly across genotypes but not across phylogenetic groupings of genotypes. A positive correlation was found between the number of substitutions in an adaptive walk and the magnitude of fitness improvement, but no correlation was found between starting and ending fitness. These results provide an empirical framework for future adaptation theory.

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Fitness improvement and the number of mutations fixed during adaptation. A significant positive correlation was found between the number of substitutions and the magnitude of fitness improvement for an adaptive walk (R2 = 0.68, F1,9 = 19.1, P = 0.002). The regression line is shown. Phylogenetic groups (see Fig. 1) are designated with different symbols
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Fig3: Fitness improvement and the number of mutations fixed during adaptation. A significant positive correlation was found between the number of substitutions and the magnitude of fitness improvement for an adaptive walk (R2 = 0.68, F1,9 = 19.1, P = 0.002). The regression line is shown. Phylogenetic groups (see Fig. 1) are designated with different symbols

Mentions: Larger fitness gains required more substitutions (Fig. 3). There was a significant positive correlation between the number of observed substitutions and the magnitude of fitness improvement (R2 = 0.68, F1,9 = 19.1, P = 0.002). The average effect over all 35 observed substitutions was a fitness increase of 1.8 doublings per hour. On average, each mutation approximately doubled the number of offspring produced in 40 min.Fig. 3


The genetics of adaptation for eight microvirid bacteriophages.

Rokyta DR, Abdo Z, Wichman HA - J. Mol. Evol. (2009)

Fitness improvement and the number of mutations fixed during adaptation. A significant positive correlation was found between the number of substitutions and the magnitude of fitness improvement for an adaptive walk (R2 = 0.68, F1,9 = 19.1, P = 0.002). The regression line is shown. Phylogenetic groups (see Fig. 1) are designated with different symbols
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2746890&req=5

Fig3: Fitness improvement and the number of mutations fixed during adaptation. A significant positive correlation was found between the number of substitutions and the magnitude of fitness improvement for an adaptive walk (R2 = 0.68, F1,9 = 19.1, P = 0.002). The regression line is shown. Phylogenetic groups (see Fig. 1) are designated with different symbols
Mentions: Larger fitness gains required more substitutions (Fig. 3). There was a significant positive correlation between the number of observed substitutions and the magnitude of fitness improvement (R2 = 0.68, F1,9 = 19.1, P = 0.002). The average effect over all 35 observed substitutions was a fitness increase of 1.8 doublings per hour. On average, each mutation approximately doubled the number of offspring produced in 40 min.Fig. 3

Bottom Line: Despite this, final fitnesses did not vary significantly among replicates.A positive correlation was found between the number of substitutions in an adaptive walk and the magnitude of fitness improvement, but no correlation was found between starting and ending fitness.These results provide an empirical framework for future adaptation theory.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Idaho, Moscow, ID 83844-3051, USA.

ABSTRACT
Theories of adaptive molecular evolution have recently experienced significant expansion, and their predictions and assumptions have begun to be subjected to rigorous empirical testing. However, these theories focus largely on predicting the first event in adaptive evolution, the fixation of a single beneficial mutation. To address long-term adaptation it is necessary to include new assumptions, but empirical data are needed for guidance. To empirically characterize the general properties of adaptive walks, eight recently isolated relatives of the single-stranded DNA (ssDNA) bacteriophage phiX174 (family Microviridae) were adapted to identical selective conditions. Three of the eight genotypes were adapted in replicate, for a total of 11 adaptive walks. We measured fitness improvement and identified the genetic changes underlying the observed adaptation. Nearly all phages were evolvable; nine of the 11 lineages showed a significant increase in fitness. However, fitness plateaued quickly, and adaptation was achieved through only three substitutions on average. Parallel evolution was rampant, both across replicates of the same genotype as well as across different genotypes, yet adaptation of replicates never proceeded through the exact same set of mutations. Despite this, final fitnesses did not vary significantly among replicates. Final fitnesses did vary significantly across genotypes but not across phylogenetic groupings of genotypes. A positive correlation was found between the number of substitutions in an adaptive walk and the magnitude of fitness improvement, but no correlation was found between starting and ending fitness. These results provide an empirical framework for future adaptation theory.

Show MeSH
Related in: MedlinePlus