Chemical Mediation of Shell-related Behaviors in Hermit Crabs

[9412679]布鲁克斯寄居蟹有柔软卷曲的腹部，可以容纳空出来的蜗牛壳。由于蟹的生长和壳被污染的生物降解，寻找新的，更大的壳是这些甲壳类动物的自然史的一个关键组成部分。寄居蟹可以通过不同的方式获得新壳。一种机制涉及寄居蟹之间的种内和种间壳交换，这可以为一个或两个参与者提供更好的壳。另一种机制涉及到受伤同种动物的位置。具体来说，几种螃蟹对它们各自同种的血液或血淋巴中的因子有反应。同源寄居蟹和其他寄居蟹的血淋巴不能引起强烈的吸引反应。寄居蟹血淋巴中的引诱剂分子只在寄居蟹（Clibanarius vitatus）一种中被研究过；它们的大小小于1000 D，可能是多肽。除此之外，人们对血淋巴引诱剂的具体化学性质或寄居蟹物种普遍存在的这种反应知之甚少。寄居蟹获得新壳的第三种机制是通过定位被捕食者吃掉的蜗牛。蜗牛的捕食者产生的蛋白水解酶触发了蜗牛肉中信号肽的释放。寄居蟹对这些肽的反应是向源头移动，等待捕食者从壳上取下肉（或直接取下捕食者留下的剩余肉）。目前尚不清楚这些引诱剂分子是否与螃蟹对血淋巴的反应相似。以前的研究也表明，一些寄居蟹物种对某些蜗牛气味有优先反应。螃蟹是如何区分这些肽信号的尚不清楚。在这三种取壳机制中，蟹壳的大小和契合度都会影响其行为和反应。也许其他变量，如共生体的存在也会影响寄居蟹的反应。在本提案中，将研究以下主题：(1)寄居蟹对血液病反应的特异性；寄居蟹对化学信号的识别；(3)蜗牛的线索和螃蟹的血淋巴在化学上是否相似；(4)壳适合度、性别和共生体的存在在介导壳可利用性线索反应中的作用。这项研究的结果将是重要的，因为涉及周围受体的肽介导的反应是罕见的。对这一新系统的研究将为化学生态学家以及行为和进化生物学家提供重要的知识。* * *

9412679 Brooks Hermit crabs possess a soft, coiled abdomen which allows the occupancy of vacated snail shells. Because of crab growth and shell degradation by fouling organisms, locating new, larger shells is a critical component in the natural history of these crustaceans. Hermit crabs can procure new shells in different ways. One mechanisms involves intra- and inter-specific shell exchanges between hermit crabs, which can result in a better shell fit for one or both participants. Another mechanism involves location of injured conspecifics. Specifically, several species of crab respond to factors in the blood or hemolymph of their respective conspecifics. Hemolymph from congeneric and other hermit crabs or brachyurans fails to elicit strong attraction responses. The attractant molecules in hermit crab hemolymph have only been investigated in one species, Clibanarius vittatus; they are less than 1000 D in size and likely peptides. Otherwise, very little is known about the specific chemical nature of the hemolymph attractant or the ubiquity of this response i hermit crab species. A third mechanism for hermit crabs obtaining new shells is by locating snails that are being consumed by predators. Proteolytic enzymes produced by predators of snails trigger the release of signal peptides from the flesh. Hermit crabs respond to these peptides by moving towards the source and waiting for the predator to remove the flesh from the shell ( or directly remove remaining flesh left behind by the predator). It is unclear whether these attractant molecules are similar to those involved in crab responses to hemolymph. Previous studies have also shown that some hermit crab species respond preferentially to certain snail odors. How crabs discriminate between these peptide signals is unknown. In all three mechanisms of shell procurement, the size and fit of the crab's present shell can influence its behavior and response. Perhaps other variables such as presence of symbionts als o influence hermit crab responses. In this proposal, the following topics will be investigated: (1) specificity of responses by hermit crabs to hemoplymph; (2) discrimination of chemical signals by hermit crabs; (3) whether snail cues and hemolymph from crabs are chemically similar molecules; and (4) the role of shell fit, sex, and presence of symbionts in mediating responses to shell availability cues. The results of this study will be significant because peptide-mediated responses involving perireceptors are uncommon. Investigation of this novel system will provide important knowledge to chemical ecologists, as well as behavioral and evolutionary biologists. ***