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.
The authors declare no competing interests.
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Weiss, L.C., Albada, B., Becker, S.M. et al. Identification of Chaoborus kairomone chemicals that induce defences in Daphnia. Nat Chem Biol 14, 1133–1139 (2018). https://doi.org/10.1038/s41589-018-0164-7
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