Schematical representation of the current knowledge on inducible defenses in Daphnia pulex. (a) Daphnia pulex forms defenses in response to chemical cues (kairomones) released by predators. Even tiny 'neckteeth', morphological changes, are protective. (b) Whereas different phenotypic defenses (adaptive changes in morphology, life-history and/or behaviour) in response to predation pressure are reported from ecological studies, little is known about the genetic mechanisms underlying these phenotypic changes. (c) Preliminary evidence for an involvement of several genes in inducible defenses exists (IS, insulin signaling; JH, juvenile hormone; UBC, ubiquitin-conjugating enzyme). (d) Concerted multidisciplinary efforts are required in the future to address and answer the question about the genetic basis of inducible defenses. QTL, quantitative trait loci; RNAi, RNA interference.