Induction of daytime downward migration in a field-derived Daphnia population by the fish kairomone CPS – a mesocosm approach

<p>The fish-borne bile salt 5α-cyprinol sulfate (CPS) has been identified as a kairomone inducing the predator avoidance behavior "diel vertical migration" (DVM) in <em>Daphnia</em> <em>magna</em> in response to fish. Conclusions about the ecological significance of CPS have been derived from laboratory experiments only. Using a mesocosm approach, we investigate whether the role of CPS as a kairomone can be confirmed in the field. We demonstrate that CPS induces downward migration during daytime in a field-derived <em>Daphnia</em> community consisting of <em>D. longispina </em>and<em> D. cucullata </em>and<em> in D. longispina</em> in particular. In the study lake, <em>D. longispina</em> shows a similar pattern of DVM. Quantification of CPS by HPLC-MS confirms that CPS in situ concentrations in the lake are sufficiently high for induction of daytime downward migration of <em>D. longispina</em> in this oligo-mesotrophic lake. Conclusively, we provide evidence for the significance of CPS as a kairomone in freshwater systems.</p>