Chemical Mediation of Shell-related Behaviors in Hermit Crabs

9412679只溪流寄居蟹拥有柔软卷曲的腹部，可以容纳空置的蜗牛壳。由于螃蟹的生长和由污染生物造成的贝壳退化，寻找新的、更大的贝壳是这些甲壳类动物自然历史中的关键组成部分。寄居蟹可以通过不同的方式获得新的贝壳。一种机制涉及寄居蟹之间的种内和种间贝壳交换，这可能导致更适合一个或两个参与者的贝壳。另一种机制涉及受伤的同种异物的位置。具体地说，几种螃蟹对它们各自同种特异体的血液或血淋巴中的因子做出反应。同属和其他寄居蟹或短毛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一个物种中被研究过，它们的大小和可能的多肽都小于1000D。除此之外，关于血淋巴引诱剂的具体化学性质或这种反应在寄居蟹物种中的普遍存在，人们知之甚少。寄居蟹获得新壳的第三种机制是通过定位正在被捕食者吃掉的蜗牛。由蜗牛捕食者产生的蛋白水解酶触发从肌肉中释放信号肽。寄居蟹对这些多肽的反应是向源头移动，等待捕食者将肉从壳中取出(或直接取出捕食者留下的剩余肉)。目前尚不清楚这些引诱剂分子是否类似于螃蟹对血淋巴的反应。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多肽信号的，目前尚不清楚。在所有三种贝壳采购机制中，螃蟹现有贝壳的大小和合适程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。在这项建议中，将研究以下主题：(1)寄居蟹对血淋巴反应的特异性；(2)寄居蟹对化学信号的识别；(3)蜗牛线索和螃蟹血淋巴是否在化学上是相似的分子；(4)贝壳适合性、性别和共生体的存在在调节对贝壳可获得性线索的反应中的作用。这项研究的结果将是有意义的，因为涉及周围型受体的多肽介导的反应并不常见。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. ***