Peptide attraction of hermit crabsClibanarius vittatus Bosc: Roles of enzymes and substrates.

Hermit crabs are obligate users of gastropod shells. Shell availability is often the limiting factor for crab population size. Crabs have an extensive behavioral repertoire for obtaining shells. Here we extend our studies of the chemical ability of crabs to locate the shells of dead and dying gastropods from a distance. We show that peptide cues generated by the action of specific proteases on specific substrates attract crabs. The specificity of the crab response is dependent upon the type of substrate as well as the suit of enzymes attacking the substrate. Single specific enzymes are not as effective as mixtures of enzymes in generating cues from pure (and totally foreign) substrates such as ovalbumin. However, the activation of trypsinogen by enterokinase yields only a single hexapeptide and results in potent crab attraction. We conclude that the specific sequence of the peptide determines attraction. Thus, the key to crab attraction is the presence of a particular sequence in a substrate and the ability of enzymes or mixtures of enzymes to release that sequence.