Facing multiple enemies: trade-offs between adaptive responses to predators and parasites in the context of inducible defences.
Final Report Abstract
In nature, organisms encounter a variety of enemies simultaneously, leading to trade-offs between adaptive responses. In predator-prey interactions, for example, a defence trait against one predator could render the prey more vulnerable to another predator. Hence, phenotypic plasticity in the prey’s defensive traits is a widespread mechanism to cope with a continuously changing predator spectrum. The costs and benefits of these inducible defences have not been explored in the context of simultaneous exposure to enemies from different functional levels, such as predators and parasites. In the here summarized research project we studied the effects of such a multiple-enemy situation. Specifically, we addressed trade-offs between prey morphological, life-history and behavioural responses to predator threats and their susceptibility to common and virulent parasites. Our target prey and host animals were waterfleas (Daphnia), which are a well-established model system in both predator-prey and host-parasite research, and thus allowed us to build on earlier developed tools and methods. We performed several laboratory experiments, in order to advance our understanding of adaptive plasticity and community dynamics in a multiple enemy context. Here we list the most important finds: 1. Daphnia induced defended morphs were significantly more vulnerable to infection by a virulent yeast parasite than undefended morphs (system: D. longispina – fish – Metschnikowia). Thus, we demonstrated a previously unknown and environmentally relevant cost to inducible defenses. 2. Some of the Daphnia responses to parasites were altered or even reversed by the presence of predator cues (system: D. longicephala – back swimmer – Metschnikowia). For example, time to maturity was further delayed when the Daphnia were exposed to both threats than under parasite stress alone. These results imply that the impact of parasites on host species depends strongly on the presence of further threats. 3. The parasite suppressed inducible defences expressed towards one predator (system: D. magna – tadpole shrimp – Metschnikowia), but not those expressed towards another predator (system: D. magna – fish – Metschnikowia). Our study suggests that as specific inducible defences differ in their costs, some might be suppressed if a target prey is additionally infected. 4. Parasite shows higher virulence at Daphnia infected at young age (system: D. magna – Metschnikowia). Thus, using experimental protocols with non-standardized time of infections might cause difficulties in comparison of the results and, eventually, can even underestimate the impact of parasites, as infection at an early lifetime may lead to more reduced fitness. 5. There was no maternal effect on offspring resistance, life histories or morphologies (system: D. magna – Metschnikowia), which is in contrast to a previous study conducted on another parasite species. We anticipate that the transfer of maternal effects in Daphnia hosts is parasite specific. Overall, this project enhances our understanding of adative phenotypic plasticity and its evolution. In addition, we show that one has to take into account many additional parameters (like age of infection or maternal effects) to better estimate the role of host-parasite (and predator-prey) interactions in aquatic systems.
Publications
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(2011). Predator-induced defence makes Daphnia more vulnerable to parasites. Evolution. 65 (5): 1482–1488
Yin M., Laforsch C., Lohr J., and Wolinska J.
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DZG (Deutsche Zoologische Gesellschaft): Saarbrücken, Germany 09-12.9.2011. The weakness of protection: inducible defences against predators make prey more vulnerable to parasites
C. Laforsch and J. Wolinska
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(2012) Fighting parasites and predators: How to deal with multiple threats? BMC Ecology, 12:12
Hesse, O., Englbrecht, W., Laforsch C., and Wolinska J.
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ASLO (Association for the Sciences of Limnology and Oceanography): Otsu, Japan 8-13.7.2012. Parasites and predators: how to deal with two stressors
W. Engelbrecht, J. Wolinska, O. Hesse, C. Laforsch
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DZG (Deutsche Zoologische Gesellschaft): Konstanz, Germany 21-24.9.2012. Encounters with predator cues alter host responses to parasite spores
W. Engelbrecht, J. Wolinska, O. Hesse, C. Laforsch
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(2013) Two threats at once: Encounters with predator cues alter host life history and morphological responses to parasite spores. Hydrobiologia Vol. 715 issue 1 pp. 93-100
Engelbrecht, W., Hesse, O., Wolinska, J. and Laforsch, C.
