Metabolic trade-offs and the maintenance of the fittest and the attest.

Department of Mathematics, Imperial College London, Huxley Building, 180 Queen's Gate, London SW7 2A7, UK.
Nature (Impact Factor: 41.46). 03/2011; 472(7343):342-6. DOI: 10.1038/nature09905
Source: PubMed


How is diversity maintained? Environmental heterogeneity is considered to be important, yet diversity in seemingly homogeneous environments is nonetheless observed. This, it is assumed, must either be owing to weak selection, mutational input or a fitness advantage to genotypes when rare. Here we demonstrate the possibility of a new general mechanism of stable diversity maintenance, one that stems from metabolic and physiological trade-offs. The model requires that such trade-offs translate into a fitness landscape in which the most fit has unfit near-mutational neighbours, and a lower fitness peak also exists that is more mutationally robust. The 'survival of the fittest' applies at low mutation rates, giving way to 'survival of the flattest' at high mutation rates. However, as a consequence of quasispecies-level negative frequency-dependent selection and differences in mutational robustness we observe a transition zone in which both fittest and flattest coexist. Although diversity maintenance is possible for simple organisms in simple environments, the more trade-offs there are, the wider the maintenance zone becomes. The principle may be applied to lineages within a species or species within a community, potentially explaining why competitive exclusion need not be observed in homogeneous environments. This principle predicts the enigmatic richness of metabolic strategies in clonal bacteria and questions the safety of lethal mutagenesis as an antimicrobial treatment.

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    • "Copiotrophic microbes, selected under resource-rich environments , are typically characterized by rapid growth rates but lower CUE relative to slower-growing oligotrophs (e.g. some fungi, actinomycetes ) with a higher CUE (Fierer et al., 2007; Maharjan et al., 2007; Lipson et al., 2008; Beardmore et al., 2011). At the community-level, the manifestation of these traits will then depend on the diversity and relative abundance of active microbial species present in the community. "

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    • "Recent studies have suggested some potential mechanisms , such as the flattening of the " fitness landscape " by the combined effects of multiple, convex trade-offs (Beardmore et al., 2011). A typical linear trade-off defines a zero-sum game, where the benefits of allocating more of a given resource to one use are counter-balanced in direct proportion by the opportunity cost of decreased benefits from alternative uses. "

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    • "We use observational and theoretical insights to guide our incorporation of microbial physiological processes into predictions of SOM stabilization. Physiological differences across species have been linked to life-history strategies optimized for different resource environments (Resat et al., 2012; Beardmore et al., 2011; Russell and Cook, 1995). For instance , in resource-rich environments, fast-growing r strategists (copiotrophs) are typically characterized by a lower MGE but higher growth rates, relative to slower-growing K strategists (oligiotrophs; Fierer et al., 2012; Ramirez et al., 2012; Fierer et al., 2007; Klappenbach et al., 2000; Pianka, 1970). "
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