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An experimental heat wave changes immune defense and life history traits in a freshwater snail

Authors

  • Katja Leicht,

    Corresponding author
    1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
    2. Department of Biological and Environmental Science, University of Jyväskylä, Jyväskylä, Finland
    • Correspondence

      Katja Leicht, Department of Aquatic Ecology, Eawag, Überlandstrasse 133, P.O. Box 611, 8600 Dübendorf, Switzerland. Tel: +41 44 823 5180;

      Fax: +41 58 765 5028; E-mail: katja.leicht@eawag.ch

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  • Jukka Jokela,

    1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
    2. ETH Zürich, Institute of Integrative Biology (IBZ), Zürich, Switzerland
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  • Otto Seppälä

    1. Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
    2. ETH Zürich, Institute of Integrative Biology (IBZ), Zürich, Switzerland
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Abstract

The predicted increase in frequency and severity of heat waves due to climate change is expected to alter disease dynamics by reducing hosts' ability to resist infections. This could take place via two different mechanisms: (1) through general reduction in hosts' performance under harsh environmental conditions and/or (2) through altered resource allocation that reduces expression of defense traits in order to maintain other traits. We tested these alternative hypotheses by measuring the effect of an experimental heat wave (25 vs. 15°C) on the constitutive level of immune defense (hemocyte concentration, phenoloxidase [PO]-like activity, antibacterial activity of hemolymph), and life history traits (growth and number of oviposited eggs) of the great pond snail Lymnaea stagnalis. We also manipulated the exposure time to high temperature (1, 3, 5, 7, 9, or 11 days). We found that if the exposure to high temperature lasted <1 week, immune function was not affected. However, when the exposure lasted longer than that, the level of snails' immune function (hemocyte concentration and PO-like activity) was reduced. Snails' growth and reproduction increased within the first week of exposure to high temperature. However, longer exposures did not lead to a further increase in cumulative reproductive output. Our results show that short experimental heat waves do not alter immune function but lead to plastic responses that increase snails' growth and reproduction. Thus, although the relative expression of traits changes, short experimental heat waves do not impair snails' defenses. Negative effects on performance get pronounced when the heat waves are prolonged suggesting that high performance cannot be maintained over long time periods. This ultimately reduces the levels of defense traits.

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