Predator identity and the role of chemical communication in Daphnia

在水生环境中，信息传递主要依赖于化学线索，即所谓的信息化学物质。特别是，通过信息化学物质远程识别捕食者的能力能够诱导潜在猎物的行为、生活史或形态的适应性变化。虽然这种诱导防御的信息化学品（即利它素）从捕食者是广泛的水生系统中，所知甚少的化学性质的线索。水蚤属的微甲壳动物在湖泊和池塘中起着关键作用，因为它们是浮游初级生产者的主要消费者，并且是较高营养水平的重要猎物。水蚤已经成为教科书的例子，说明捕食者释放的利它素诱导防御。水蚤对鱼类释放的利它素的反应表现为昼夜垂直迁移行为、形态变化和生活史的变化。直到最近，我们才鉴定出利它素，利它素是从鲤科鱼类中释放的，诱导DVM和形态变化的胆汁盐5α-鲤鱼醇硫酸盐（5α-CPS）。然而，5α-CPS在其他淡水鱼中不存在，尽管它们在水蚤中化学诱导相同的防御。这就提出了一个问题是什么样的化学基础诱导防御水蚤在响应非鲤科鱼类，以及它是如何实现的，不同的捕食者身份的鱼来作为不同的利它素收敛到诱导相同的防御水蚤。在这里，我建议阐明各自的利它素的鲈鱼，这是广泛的和一个重要的捕食者的浮游动物。鲈鱼不合成5α-CPS，我们的初步研究表明，鲈鱼孵化水提取物能诱导DVM，并改变水蚤的生活史和形态，而鲈鱼胆汁则不能。因此，与鲤科鱼类的情况不同，鲈鱼胆汁中不存在未知的鲈鱼利它素。我建议使用重复轮的生物测定引导分馏的提取物的鲈鱼孵化水的HPLC耦合到高分辨率MS和随后的非靶向代谢组学，以确定鲈鱼利它素诱导DVM和形态和生活史的变化。如果利它素的鉴定完成，利它素释放率从鲈鱼和阈值浓度诱导DVM将允许确定水蚤是否有不同的敏感性，不同的鱼类，即鲤科鱼类和鲈鱼。我们将通过测定不同体型的水蚤中5-α-CPS和鲈鱼利它素的阈值浓度，进一步检验体型较小的水蚤具有较高的利它素诱导DVM的阈值的假设。

In aquatic environments information transfer largely depends on chemical cues, so called infochemicals. In particular, the capability to remotely recognize predators by infochemicals enables the induction of adaptive changes in behavior, life-history or morphology in potential prey. Although this induction of defenses by infochemicals (i.e. kairomones) from predators is widespread in aquatic systems, little is known about the chemical nature of the cues involved. Microcrustaceans of the genus Daphnia play a key role in lakes and ponds, as they are major consumers of planktonic primary producers and are important prey for higher trophic levels. Daphnia have become text book examples for the induction of defenses by kairomones released by predators. In response to kairomones released by fish, the major predator of daphnids, Daphnia deploy anti-predator defenses as diel vertical migration behavior (DVM), changes in morphology and in life-history. Only recently we have identified the kairomone the kairomone released from cyprinid fish that induces DVM and morphological changes as the bile salt 5α-cyprinol sulfate (5α-CPS). However, 5α-CPS is absent in other freshwater fish, although they chemically induce the same defenses in Daphnia. This raises the question what the chemical basis of induction of defenses in Daphnia in response to non-cyprinid fish species is and how it is achieved that different predator identities in fish coming as different kairomones converge into the induction of identical defenses in Daphnia. Here I propose to elucidate the respective kairomones of perch, which is widespread and an important predator of zooplankton. Percidae do not synthesize 5α-CPS, and our preliminary work demonstrates that extract of perch incubation water induces DVM and changes in life-history and morphology of Daphnia, but perch bile does not. Hence, different from the situation in Cyprindae, the unknown perch kairomones is not present in perch bile. I propose to use repeated rounds of bioassay-guided fractionation of extract of perch incubation water by HPLC coupled to high-resolution MS and subsequent non-targeted metabolomics to identify the perch kairomones that induce DVM and changes in morphology and life-history. If identification of the kairomones is accomplished, kairomone release rates from perch and threshold concentrations for the induction of DVM will allow to determine if Daphnia have different sensitivities to different fish species, i.e. to cyprinid fish and to perch. We will further test the hypothesis that Daphnia species with smaller body size have higher kairomone thresholds for the induction of DVM by determining threshold concentration of 5-α-CPS and of the perch kairomone across Daphnia species with different body sizes.