Chemical Mediation of Shell-related Behaviors in Hermit Crabs

点击翻译按钮获取中文摘要

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. ***