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Wider access to genotypic space facilitates loss of cooperation in a bacterial mutator.

Harrison F, Buckling A - PLoS ONE (2011)

Bottom Line: The impact of responses to non-social selection pressures on social evolution is arguably an under-examined area.In this paper, we consider how the evolution of a non-social trait--hypermutability--affects the cooperative production of iron-scavenging siderophores by the opportunistic human pathogen Pseudomonas aeruginosa.This may represent a novel cost of hypermutability.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Oxford, Oxford, United Kingdom. freya.harrison@zoo.ox.ac.uk

ABSTRACT
Understanding the ecological, evolutionary and genetic factors that affect the expression of cooperative behaviours is a topic of wide biological significance. On a practical level, this field of research is useful because many pathogenic microbes rely on the cooperative production of public goods (such as nutrient scavenging molecules, toxins and biofilm matrix components) in order to exploit their hosts. Understanding the evolutionary dynamics of cooperation is particularly relevant when considering long-term, chronic infections where there is significant potential for intra-host evolution. The impact of responses to non-social selection pressures on social evolution is arguably an under-examined area. In this paper, we consider how the evolution of a non-social trait--hypermutability--affects the cooperative production of iron-scavenging siderophores by the opportunistic human pathogen Pseudomonas aeruginosa. We confirm an earlier prediction that hypermutability accelerates the breakdown of cooperation due to increased sampling of genotypic space, allowing mutator lineages to generate non-cooperative genotypes with the ability to persist at high frequency and dominate populations. This may represent a novel cost of hypermutability.

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Relative fitnesses of cheat clones derived from the wild type (panel (a), n = 14) and mutator (panel (b), n = 18) populations described in [16].Fitness was measured in competition with cooperating bacteria at initially low (c.5%) and high (c.50%) cheat frequency. Diamonds show medians and associated 95% confidence intervals.
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pone-0017254-g001: Relative fitnesses of cheat clones derived from the wild type (panel (a), n = 14) and mutator (panel (b), n = 18) populations described in [16].Fitness was measured in competition with cooperating bacteria at initially low (c.5%) and high (c.50%) cheat frequency. Diamonds show medians and associated 95% confidence intervals.

Mentions: As shown in Figure 1, both strains produce cheat clones that have a relative fitness >1 in the low-frequency condition. The larger variance in fitness among mutator-derived clones appeared to be driven by two outliers as the difference in variance was not statistically significant (Levene's test: test statistic = 1.21, p = 0.279). The median fitness of wild-type derived cheats was 0.94 and this was not significantly different from 1 (Wilcoxon signed rank test, H = 45, p = 0.660); the median fitness of mutator-derived cheats was 1.48 and this was significantly greater than 1 (H = 157, p = 0.001). Therefore, both genotypes produce cheats that can invade cooperating populations from rare and the range of relative fitnesses reachable by each ancestral genotype is similar.


Wider access to genotypic space facilitates loss of cooperation in a bacterial mutator.

Harrison F, Buckling A - PLoS ONE (2011)

Relative fitnesses of cheat clones derived from the wild type (panel (a), n = 14) and mutator (panel (b), n = 18) populations described in [16].Fitness was measured in competition with cooperating bacteria at initially low (c.5%) and high (c.50%) cheat frequency. Diamonds show medians and associated 95% confidence intervals.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3045467&req=5

pone-0017254-g001: Relative fitnesses of cheat clones derived from the wild type (panel (a), n = 14) and mutator (panel (b), n = 18) populations described in [16].Fitness was measured in competition with cooperating bacteria at initially low (c.5%) and high (c.50%) cheat frequency. Diamonds show medians and associated 95% confidence intervals.
Mentions: As shown in Figure 1, both strains produce cheat clones that have a relative fitness >1 in the low-frequency condition. The larger variance in fitness among mutator-derived clones appeared to be driven by two outliers as the difference in variance was not statistically significant (Levene's test: test statistic = 1.21, p = 0.279). The median fitness of wild-type derived cheats was 0.94 and this was not significantly different from 1 (Wilcoxon signed rank test, H = 45, p = 0.660); the median fitness of mutator-derived cheats was 1.48 and this was significantly greater than 1 (H = 157, p = 0.001). Therefore, both genotypes produce cheats that can invade cooperating populations from rare and the range of relative fitnesses reachable by each ancestral genotype is similar.

Bottom Line: The impact of responses to non-social selection pressures on social evolution is arguably an under-examined area.In this paper, we consider how the evolution of a non-social trait--hypermutability--affects the cooperative production of iron-scavenging siderophores by the opportunistic human pathogen Pseudomonas aeruginosa.This may represent a novel cost of hypermutability.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Oxford, Oxford, United Kingdom. freya.harrison@zoo.ox.ac.uk

ABSTRACT
Understanding the ecological, evolutionary and genetic factors that affect the expression of cooperative behaviours is a topic of wide biological significance. On a practical level, this field of research is useful because many pathogenic microbes rely on the cooperative production of public goods (such as nutrient scavenging molecules, toxins and biofilm matrix components) in order to exploit their hosts. Understanding the evolutionary dynamics of cooperation is particularly relevant when considering long-term, chronic infections where there is significant potential for intra-host evolution. The impact of responses to non-social selection pressures on social evolution is arguably an under-examined area. In this paper, we consider how the evolution of a non-social trait--hypermutability--affects the cooperative production of iron-scavenging siderophores by the opportunistic human pathogen Pseudomonas aeruginosa. We confirm an earlier prediction that hypermutability accelerates the breakdown of cooperation due to increased sampling of genotypic space, allowing mutator lineages to generate non-cooperative genotypes with the ability to persist at high frequency and dominate populations. This may represent a novel cost of hypermutability.

Show MeSH
Related in: MedlinePlus