5α-cyprinol sulfate, a bile salt from fish, induces diel vertical migration in Daphnia

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 behavioural 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 isolated the kairomone from fish incubation water and identified it 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.

猎物面临着最小化捕食损失的选择压力。在水生环境中，多数猎物会利用捕食者释放的化学信号（chemical cues）启动反捕食行为。行为性反捕食行为的典型案例之一，是淡水微型甲壳动物溞属（Daphnia spp.）的昼夜垂直迁移（diel vertical migration, DVM），该行为由浮游食性鱼类释放的利它素（kairomones）诱导产生。本研究采用生物活性导向分离策略（bioassay-guided approach），结合液相色谱（liquid chromatography）与质谱（mass spectrometry）技术，从鱼类培育水中分离得到该利它素，并鉴定其为5α-cyprinol sulfate——该物质可在皮摩尔浓度下诱导溞属产生DVM行为。5α-cyprinol sulfate在鱼类脂质消化中发挥的作用，解释了从进化视角来看，尽管释放该物质对释放者（即鱼类）存在不利之处，但鱼类并未停止分泌该物质的原因。该诱导DVM的利它素的鉴定，使得研究其时空分布以及感知该物质的潜在分子机制成为可能，此外还可用于检验其他水生无脊椎动物中鱼类介导的诱导防御是否均由该化合物触发。