Volatile shell-investigation cues of land hermit crabs: Effect of shell fit, detection of cues from other hermit crab species, and cue isolation

Land hermit crab responses to volatile shell-investigation cues from land hermit crabs and from marine hermit crabs are analogous to the responses of marine hermit crabs to shell-investigation cues from marine crabs and from snails. Land hermit crabs attracted to shell cues are in worse-fitting shells and are more likely to investigate conspecifics' shells than are crabs attracted to feeding cues. Moving land hermit crabs from worse shells to better shells decreases the number of crabs investigating shells, while moving crabs from better shells to worse shells increases the number of crabs investigating shells. Gravid females have better-fitting shells than nongravid females or males. Crabs from two different populations in Panama have different shell fits and show different levels of responses to shell-investigation cues. Land hermit crabs respond to volatile shell-investigation cues from both land and marine hermit crabs, but marine hermit crabs do not respond to cues from land hermit crabs. A cue detection system for volatile cues most likely evolved in land hermit crabs during their transition from a marine to a terrestrial existence. Thus, the cues found in land hermit crabs and marine hermit crabs may be chemically similar. Volatile compounds collected from hermit crabs onto Tenax columns can be eluted with ethanol and act as shell-investigation cues in field assays.