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Open Access Research article

Fighting parasites and predators: How to deal with multiple threats?

Olivia Hesse1, Wolfgang Engelbrecht1, Christian Laforsch12* and Justyna Wolinska1

Author Affiliations

1 Department of Biology II, Ludwig-Maximilians-University Munich, Grosshaderner Str 2, 82152, Planegg-Martinsried, Germany

2 GeoBio Center, Ludwig-Maximilians-University Munich, Munich, Germany

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BMC Ecology 2012, 12:12  doi:10.1186/1472-6785-12-12

Published: 24 July 2012

Abstract

Background

Although inducible defences have been studied extensively, only little is known about how the presence of parasites might interfere with these anti-predator adaptations. Both parasites and predators are important factors shaping community structure and species composition of ecosystems. Here, we simultaneously exposed Daphnia magna to predator cues (released by the tadpole shrimp, Triops, or by a fish) and spores of the yeast parasite Metschnikowia sp. to determine how life history and morphological inducible defences against these two contrasting types of predators are affected by infection.

Results

The parasite suppressed some Triops-induced defences: Daphnia lost the ability to produce a greater number of larger offspring, a life-history adaptation to Triops predation. In contrast, the parasite did not suppress inducible defences against fish: induction (resulting in smaller body length of the mothers as well as of their offspring) and infection acted additively on the measured traits. Thus, fish-induced defences may be less costly than inducible defences against small invertebrate predators like Triops; the latter defences could no longer be expressed when the host had already invested in fighting off the parasite.

Conclusions

In summary, our study suggests that as specific inducible defences differ in their costs, some might be suppressed if a target prey is additionally infected. Therefore, adding parasite pressure to predator–prey systems can help to elucidate the costs of inducible defences.

Keywords:
Daphnia; Host-parasite; Inducible defences; Metschnikowia sp.; Multiple stressors; Phenotypic plasticity; Predator–prey