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Fitness and virulence of a bacterial endoparasite in an environmentally stressed crustacean host

Published online by Cambridge University Press:  21 July 2010

ANJA COORS*
Affiliation:
Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, Ch. De Bériotstraat 32, 3000 Leuven, Belgium
LUC DE MEESTER
Affiliation:
Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, Ch. De Bériotstraat 32, 3000 Leuven, Belgium
*
*Corresponding author, present address: ECT Oekotoxikologie GmbH, Boettgerstraße 2-14, 65439 Flörsheim a.M., Germany. Tel: +49 6145 9564 20. Fax: +49 6145 9564 99. E-mail: [email protected]

Summary

Host-parasite interactions are shaped by the co-evolutionary arms race of parasite virulence, transmission success as well as host resistance and recovery. The virulence and fitness of parasites may depend on host condition, which is mediated, for instance, by host energy constraints. Here, we investigated to what extent stress imposed by predation threat and environmental pollutants influences host-parasite interactions. We challenged the crustacean host Daphnia magna with the sterilizing bacterial endoparasite Pasteuria ramosa and simultaneously exposed the host to fish kairomones, the pesticide carbaryl or both stressors. While parasite virulence, measured as impact on host mortality and sterilization, increased markedly after short-term pesticide exposure, it was not influenced by predation threat. Parasite fitness, measured in terms of produced transmission stages, decreased both in fish and pesticide treatments. This effect was much stronger under predation threat than carbaryl exposure, and was attributable to reduced somatic growth of the host, presumably resulting in fewer resources for parasite development. While the indirect impact of both stressors on spore loads provides evidence for host condition-dependent parasite fitness, the finding of increased virulence only under carbaryl exposure indicates a stronger physiological impact of the neurotoxic chemical compared with the effect of a non-toxic fish kairomone.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2010

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