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Host–parasite coevolutionary arms races give way to fluctuating selection

Authors

  • Alex R. Hall,

    Corresponding author
    1. Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
      E-mail:alex.hall@zoo.ox.ac.uk
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    • These authors contributed equally to this work

  • Pauline D. Scanlan,

    1. Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
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    • These authors contributed equally to this work

  • Andrew D. Morgan,

    1. Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
    2. Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3JT, UK
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  • Angus Buckling

    1. Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
    2. College of Life & Environmental Sciences, University of Exeter, Cornwall Campus, Penryn TR10 9EZ, UK
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E-mail:alex.hall@zoo.ox.ac.uk

Abstract

Ecology Letters (2011) 14: 635–642

Abstract

Host–parasite coevolution is a key driver of biological diversity and parasite virulence, but its effects depend on the nature of coevolutionary dynamics over time. We used phenotypic data from coevolving populations of the bacterium Pseudomonas fluorescens SBW25 and parasitic phage SBW25Φ2, and genetic data from the phage tail fibre gene (implicated in infectivity evolution) to show that arms race dynamics, typical of short-term studies, decelerate over time. We attribute this effect to increasing costs of generalism for phages and bacteria with increasing infectivity and resistance. By contrast, fluctuating selection on individual host and parasite genotypes was maintained over time, becoming increasingly important for the phenotypic properties of parasite and host populations. Given that costs of generalism are reported for many other systems, arms races may generally give way to fluctuating selection in antagonistically coevolving populations.

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