Abstract
Prey are under selection to minimize predation losses. In aquatic environments, many prey use chemical cues released by predators, which initiate predator avoidance. A prominent example of behavioral predator-avoidance constitutes diel vertical migration (DVM) in the freshwater microcrustacean Daphnia spp., which is induced by chemical cues (kairomones) released by planktivorous fish. In a bioassay-guided approach using liquid chromatography and mass spectrometry, we identified the kairomone from fish incubation water as 5α-cyprinol sulfate inducing DVM in Daphnia at picomolar concentrations. The role of 5α-cyprinol sulfate in lipid digestion in fish explains why from an evolutionary perspective fish has not stopped releasing 5α-cyprinol sulfate despite the disadvantages for the releaser. The identification of the DVM-inducing kairomone enables investigating its spatial and temporal distribution and the underlying molecular mechanism of its perception. Furthermore, it allows to test if fish-mediated inducible defenses in other aquatic invertebrates are triggered by the same compound.
Highlights
Predation is recognized as an important selective force which has been shown to drive the shape of trophic cascades and numerous aspects of ecosystem ecology (Gliwicz, 1986; Lima, 1998; Werner and Peacor, 2003)
We identified an infochemical that Daphnia uses to perceive the risk of being preyed upon by planktivorous fish
We show that the induction of diel vertical migration (DVM) in Daphnia is dependent on a particular bile compound from fish, that is 5a-cyprinol sulfate (a-CPS), which is active already at a concentration of 100 pM
Summary
Predation is recognized as an important selective force which has been shown to drive the shape of trophic cascades and numerous aspects of ecosystem ecology (Gliwicz, 1986; Lima, 1998; Werner and Peacor, 2003) Such effects of predators are caused by predation (direct consumptive effect; Preisser et al, 2005) or by effects on plastic behavioral, physiological or morphological traits of prey seeking to avoid predation (indirect, non-consumptive effect, (Heithaus et al, 2008; Lima, 1998; Moll et al, 2017; Werner and Peacor, 2003). The induction of defenses by chemical cues from predators is widespread in aquatic systems (Bjærke et al, 2014; Bronmark and Hansson, 2012), and recently progress has been made by identification of chemical cues involved in aquatic predator-prey chemical communication (Poulin et al, 2018; Selander et al, 2015; Weiss et al, 2018)
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