Predator identity and the role of chemical communication in Daphnia

• Applicant: Professor Dr. Eric von Elert, Ph.D.
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 535780508

In aquatic environments information transfer largely depends on chemical cues, so called infochemicals. In particular, the capability to remotely recognize predators by infochemicals enables the induction of adaptive changes in behavior, life-history or morphology in potential prey. Although this induction of defenses by infochemicals (i.e. kairomones) from predators is widespread in aquatic systems, little is known about the chemical nature of the cues involved. Microcrustaceans of the genus Daphnia play a key role in lakes and ponds, as they are major consumers of planktonic primary producers and are important prey for higher trophic levels. Daphnia have become text book examples for the induction of defenses by kairomones released by predators. In response to kairomones released by fish, the major predator of daphnids, Daphnia deploy anti-predator defenses as diel vertical migration behavior (DVM), changes in morphology and in life-history. Only recently we have identified the kairomone the kairomone released from cyprinid fish that induces DVM and morphological changes as the bile salt 5α-cyprinol sulfate (5α-CPS). However, 5α-CPS is absent in other freshwater fish, although they chemically induce the same defenses in Daphnia. This raises the question what the chemical basis of induction of defenses in Daphnia in response to non-cyprinid fish species is and how it is achieved that different predator identities in fish coming as different kairomones converge into the induction of identical defenses in Daphnia. Here I propose to elucidate the respective kairomones of perch, which is widespread and an important predator of zooplankton. Percidae do not synthesize 5α-CPS, and our preliminary work demonstrates that extract of perch incubation water induces DVM and changes in life-history and morphology of Daphnia, but perch bile does not. Hence, different from the situation in Cyprindae, the unknown perch kairomones is not present in perch bile. I propose to use repeated rounds of bioassay-guided fractionation of extract of perch incubation water by HPLC coupled to high-resolution MS and subsequent non-targeted metabolomics to identify the perch kairomones that induce DVM and changes in morphology and life-history. If identification of the kairomones is accomplished, kairomone release rates from perch and threshold concentrations for the induction of DVM will allow to determine if Daphnia have different sensitivities to different fish species, i.e. to cyprinid fish and to perch. We will further test the hypothesis that Daphnia species with smaller body size have higher kairomone thresholds for the induction of DVM by determining threshold concentration of 5-α-CPS and of the perch kairomone across Daphnia species with different body sizes.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Carlos Sánchez-Arcos