Zooplankton Photoresponses during Diel Vertical Migration: Modificaiton by Chemical Cues from Predators

大多数浮游动物在发育的某个阶段都经历了垂直迁移。常见的模式包括接近日落的上升和接近日出的下降。最普遍的功能解释是，动物在夜间上升进食，白天下降以躲避视觉导向的捕食者。最近的研究表明，浮游生物的存在和不存在可以通过快速的行为改变来改变DVM。由于光是DVM最重要的线索，来自捕食者的线索在迁徙过程中的变化应该涉及光反应的变化。因此，光反应可以作为一种行为分析来指导对捕食者化学线索(S)的表征、纯化和鉴定。这个项目的目标是：(1)确定是否有浮游动物(鱼类)和不能看到猎物的浮游动物(线虫和毛藻)的存在或不存在改变了参与DVM的光反应，(2)确定来自捕食者的化学线索是否会引起参与DVM的浮游动物光反应的改变，以及(3)描述捕食者的化学线索。中华绒螯蟹Rhithropanopeus harrisii和卤虫Artemia sp.将被研究，因为两者都经历了DVM，初步研究表明，它们的光反应会被浮游动物的化学信号改变。光响应将通过视频系统进行监控，并在模拟自然水下角光分布的设备中进行测试。初步研究表明，来自鱼类的活性化学物质的分子大小不到500道尔顿，研究人员预测，这些具有生物活性的分子是由鱼类表面常见的分子水解产生的气味。来自鱼粘液的双糖和来自上皮蛋白的小肽可能是候选的。

Most zooplankton undergo diel vertical migration (DVM) at some stage of development. The common pattern involves an ascent near sunset and descent near sunrise. The most pervasive functional explanations are that animals rise to feed at night and descend to avoid visually-oriented predators during the day. Recent studies indicate the presence and absence of planktivores can alter DVM through rapid behavioral changes. Since light is the most important cue for DVM, alterations in migration by cues from predators should involve changes in photoresponses. Thus, photoresponses can be used as a behavioral assay to direct characterization, purification and identification of the chemical cue(s) from predators. The objectives of this project are: (1) to determine whether photoresponses involved in DVM are altered by the presence or absence of planktivores that do (fish) and do not (ctenophore and chaetognath) visually sight their prey, (2) to determine whether chemical cues form predators induce alterations in zooplankton photoresponses that are involved in DVM, and (3) to characterize the chemical cues form the predators. Larvae of the crab Rhithropanopeus harrisii and of brine shrimp (Artemia sp.) will be studied because both undergo DVM and preliminary studies suggest their photoresponses are altered by chemical cues from planktivores. Photoresponses will be monitored with a video system and tested in an apparatus that mimics the natural underwater angular light distribution. Preliminary studies indicate the active chemicals from fish are less than 500 Daltons in molecular size and the investigators predict that the biologically active molecules are odors generated by hydrolysis of molecules found commonly on fish surfaces. Disaccharides originating form fish mucus, and small peptides originating from epithelial proteins are likely candidates.