Chemosensory Mechanisms Regulating Predation

捕食是调节猎物数量的主要生物力量，对群落结构也有很强的影响。有证据表明，嗅觉对许多陆生和水生动物的掠食性搜索起着中介作用。然而，过去的研究并没有将嗅觉介导的搜索或引导机制的成功程度与猎物产生化学引诱剂或自然发生捕食活动的水力环境联系起来。利用蓝蟹（Callinectes sapidus）和硬蛤（Mercenaria Mercenaria）之间的捕食者-猎物相互作用，本项目将研究捕食者的嗅觉基础。螃蟹捕食搜索行为的分析结果将指导完整活蛤释放肽引诱剂的化学分馏和分离。从主动抽吸蛤的外流虹吸管中收集的水将被划分为不同的分子量类别，并通过选择性酶降解来探测肽结构。随着引诱剂的分离和鉴定，将对纯化合物进行效价（剂量-反应）和潜在的混合相互作用的生物测定。通过这种方式，自然配体将被发现，并可用于区分触角和腿在化学感觉中的作用，这些化学感觉介导了螃蟹的掠食性搜索行为。然后将测量蛤的水交换率和引诱剂通量，并设计蛤释放引诱剂的生物力学和化学模型。将在一个大型（10米长）水槽中模拟自然栖息地的流动，在受控的水动力条件下测试螃蟹寻找蛤块的能力。作为最后的测试，将在现场重复选定的实验，使用活蛤和模型作为自由放养的螃蟹的引诱源。因此，该项目将为嗅觉作为捕食者-猎物相互作用的调节因素提供迄今为止最严格的测试。它将产生新的引诱剂结构，用于基本化学感觉过程的细胞和分子研究，同时它将提供捕食者嗅觉和猎物对捕食者的脆弱性之间的关键联系。最后，它可以为未来的研究开辟重要的途径，探索猎物可能通过采取风险敏感的代谢策略来保护自己的机制，在这种策略中，当发现附近的捕食者时，引诱剂的产生就会停止。

Predation is a major biotic force regulating prey populations, as well as exerting strong effects on community structure. Evidence suggests that the sense of smell mediates predatory search in many terrestrial and aquatic animals. Past investigations have not, however, been designed to link either the degree of successful olfactory-mediated search or guidance mechanisms with the production of chemical attractant by prey or the hydraulic environment in which predatory activities naturally take place. Using the predator - prey interaction between blue crabs (Callinectes sapidus) and hard clams (Mercenaria mercenaria), this project will investigate the olfactory basis for predation. Results from assays of crab predatory search behavior will guide chemical fractionation and isolation of peptide attractants being released by intact live clams. Water collected from the excurrent siphons of actively pumping clams will be characterized by partitioning into different molecular weight classes and by using selective enzyme degradation to probe peptide structures. As attractants are isolated and identified, pure compounds will be bioassayed for potency (dose-response) and for potential mixture interactions. In this manner, the natural ligands will be discovered and made available for discriminating between the roles of antennules and legs in chemosensation that mediates crab predatory search behavior. The rates of water exchange and attractant flux will then be measured for clams, and a biomechanical and chemical model of a clam releasing attractants will be engineered. Crab ability to find clam patches will be tested under controlled hydrodynamic conditions in a large (10-m long) flume, simulating flow in the natural habitat. As a final test, selected experiments will be repeated in the field by using live clams and models as attractant sources to free-ranging crabs. This project will thus provide the most rigorous test to date of olfaction as a regulatory factor in predator-prey interactions. It will yield new attractant structures for use in cellular and molecular studies on basic chemosensory processes, while it will provide a critical link between the olfactory sense of predators and prey vulnerability to predation. Finally, it could open significant avenues for future research to explore the mechanisms through which prey might defend themselves by adopting risk-sensitive metabolic strategies in which attractant production stops when nearby predator are detected.