Perceiving environmental information is crucial for organisms to locate resources and avoid predation. In freshwater ecosystems, species of the microcrustacean Daphnia develop inducible defences in response to predator-specific chemical cues, which confer measurable fitness advantages. While some predator-specific chemicals have been identified, the receptors mediating detection of these chemicals remain poorly described. Because these inducible responses depend on the detection of predator-derived chemicals, understanding the underlying chemosensory machinery is critical for elucidating predator-prey dynamics per se and their modification under environmental change. We analysed the contribution of an ancient subfamily of ionotropic receptors co-opted for chemosensation in protostomes. Using evolutionary conservation of IR25a and IR93a across arthropods, we identified and characterized their Daphnia homologues. Multi-species analysis reveals these co-receptors are essential for detecting predator-specific cues. When predators are present, IR25a and IR93a are upregulated, and the corresponding proteins localize to the chemosensory antennules, supporting their involvement in predator cue detection. RNA interference-mediated knockdown of these co-receptors attenuates species-specific defences. These findings identify IR25a and IR93a as required mediators of chemosensory signal transduction in predator detection. Together, our results reveal a conserved ionotropic receptor pathway that mechanistically connects predator cue detection to inducible defensive plasticity, advancing our molecular understanding of predator-prey interactions.
Graeve et al. (Wed,) studied this question.