Food quantity and quality effects on inducible defences in freshwater zooplankton

• Applicants: Dr. Marvin Kiene; Professor Dr. Christian Laforsch; Professor Dr. Dominik Martin-Creuzburg
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 573363544

Predation is a strong and ubiquitous driver of evolution and ecosystem functioning. In response to predation pressure, many prey species have evolved defences that reduce predation impact. This phenotypic plasticity in defensive traits in prey, so-called inducible defences, is a widespread mechanism to cope with a frequently changing predation risk while reducing the costs that come with the development of defences. In addition to predation, constraints in food quantity and quality are common in natural systems, but the predator induced plasticity may imply changing demands in food quantity and quality, e.g., for changes in morphology or life history. Therefore, the composition of the phytoplankton community, and thereby the nutrient availability for grazers, may lead to nutrient limitations that potentially constrain the expression of defences. Nonetheless, studies on the effects of food quantity and/or food quality on the expression of inducible defences are scarce and those effects and costs are poorly understood. But especially costs are central for the understanding of observed response patterns. To get a comprehensive understanding of how food quantity and quality shape the prey’s response to predation, we propose to investigate the reaction norm against variable predators (i.e., evoking different response strategies) in the waterflea Daphnia magna, a freshwater keystone species and model organism. We will decipher the underlying trade-offs and mechanisms of the defence induction covering food quantity (i.e., carbon), food quality (cholesterol and EPA) as well as predator species and density (i.e., predation risk). To get additional insight into nutrient allocation strategies, we further assess the lipid body content (cholesterol and PUFA) of the experimental prey animals at two points of their life cycle. Furthermore, the assessment of the intra-specific variability of responses and their costs can provide insight into the susceptibility of natural populations to these constraints. The here proposed project, assessing the complex trade-offs in the adaptive responses to predation and dietary constraints will provide a better mechanistic understanding of inducible defences in natural environments, and how the defences are affected by changes in the phytoplankton community composition. This will contribute to our understanding of trophic interactions, population dynamics and food-web processes.

• DFG Programme: Research Grants