Infochemicals play important roles in aquatic ecosystems. They even modify food web interactions, such as by inducing defenses in prey. In one classic but still not fully understood example, the planktonic freshwater crustacean Daphnia pulex forms specific morphological defenses (neckteeth) induced by chemical cues (kairomones) released from its predator, the phantom midge larva Chaoborus. On the basis of liquid chromatography, mass spectrometry, and chemical synthesis, we report here the chemical identity of the Chaoborus kairomone. The biologically active cues consist of fatty acids conjugated to the amino group of glutamine via the N terminus. These cues are involved in Chaoborus digestive processes, which explains why they are consistently released despite the disadvantage for its emitter. The identification of the kairomone may allow in-depth studies on multiple aspects of this inducible defense system.

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We dedicate our study to the memory of our inspiring friend S. Dodson. He would have loved to see the results. We thank G. Pohnert for discussion and S. Gorb and S. Kruppert for providing the Chaoborus predation sequence. We thank L. Weider (University of Oklahoma) for the R9 clone and T. White for language editing.

Author information


  1. Department of Animal Ecology, Evolution and Biodiversity, Faculty of Biology and Biotechnology, Ruhr University Bochum, Bochum, Germany

    • Linda C. Weiss
    • , Sina M. Becker
    • , Markus Leo
    •  & Ralph Tollrian
  2. Inorganic Chemistry 1–Bioinorganic Chemistry, Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Bochum, Germany

    • Bauke Albada
    • , Johannes Zagermann
    •  & Nils Metzler-Nolte
  3. Laboratory of Organic Chemistry, Wageningen University and Research, Wageningen, The Netherlands

    • Bauke Albada
  4. Applied Analytical Chemistry, Faculty of Chemistry, University of Duisburg-Essen, Essen, Germany

    • Sven W. Meckelmann
    • , Julia Klein
    • , Martin Meyer
    •  & Oliver J. Schmitz
  5. NERC Biomolecular Analysis Facility Metabolomics Node (NBAF-B), School of Biosciences, University of Birmingham, Birmingham, UK

    • Ulf Sommer


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L.C.W. and R.T. designed the research; M.L. performed the initial ESI–MS analysis, J.Z. prepared the first kairomone derivative; L.C.W. and R.T. designed and L.C.W. and S.M.B. conducted biological experiments; B.A. and N.M.-N. prepared the synthetic kairomone derivatives, U.S. performed chemical analysis; S.W.M., J.K., M.M., and O.J.S. quantified the kairomone concentration; L.C.W., R.T., B.A., and N.M.-N. wrote the manuscript; all authors contributed to the final version of the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Ralph Tollrian.

Supplementary information

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    Supplementary Tables 1–6, Supplementary Figures 1–8

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  3. Supplementary Note 1

    Synthetic Procedures

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