Variation in costs of parasite resistance among natural host populations

Authors

  • S. K. J. R. Auld,

    Corresponding author
    1. School of Natural Sciences, University of Stirling, Stirling, UK
    2. School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
    • Correspondence: Stuart K. J. R. Auld, School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK. Tel.: +44 1786 467810; fax: +44 1786 467843; e-mail: s.k.auld@stir.ac.uk

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  • R. M. Penczykowski,

    1. School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
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  • J. Housley Ochs,

    1. School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
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  • D. C. Grippi,

    1. School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
    Current affiliation:
    1. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA
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  • S. R. Hall,

    1. Department of Biology, Indiana University, Bloomington, IN, USA
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  • M. A. Duffy

    1. School of Biology, Georgia Institute of Technology, Atlanta, GA, USA
    Current affiliation:
    1. Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI, USA
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Abstract

Organisms that can resist parasitic infection often have lower fitness in the absence of parasites. These costs of resistance can mediate host evolution during parasite epidemics. For example, large epidemics will select for increased host resistance. In contrast, small epidemics (or no disease) can select for increased host susceptibility when costly resistance allows more susceptible hosts to outcompete their resistant counterparts. Despite their importance for evolution in host populations, costs of resistance (which are also known as resistance trade-offs) have mainly been examined in laboratory-based host–parasite systems. Very few examples come from field-collected hosts. Furthermore, little is known about how resistance trade-offs vary across natural populations. We addressed these gaps using the freshwater crustacean Daphnia dentifera and its natural yeast parasite, Metschnikowia bicuspidata. We found a cost of resistance in two of the five populations we studied – those with the most genetic variation in resistance and the smallest epidemics in the previous year. However, yeast epidemics in the current year did not alter slopes of these trade-offs before and after epidemics. In contrast, the no-cost populations showed little variation in resistance, possibly because large yeast epidemics eroded that variation in the previous year. Consequently, our results demonstrate variation in costs of resistance in wild host populations. This variation has important implications for host evolution during epidemics in nature.

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