Use of chemical cues during shell fights in the hermit crab Pagurus bernhardus

Abstract

AbstractChemical communication is likely to play an important role during agonistic encounters in aquatic crustaceans but the use of chemical signals is difficult to observe. An alternative approach to direct observation is to collect water that has contained fighting animals and then expose a focal animal of the same species to the cue water and monitor its behaviour. Here we investigate the possibility of the use of chemical cues during 'shell fights' in the hermit crab Pagurus bernhardus. Focal crabs exposed to the fighting cue spent more time withdrawn into their gastropod shell, less time on locomotion and less time searching for food than did those exposed to cues from non-fighting hermit crabs or those treated with plain sea water. At the end of the observation period we used a novel stimulus to induce a startle response in order to probe the focal crab's motivational state for this exploratory behaviour. Those exposed to the fighting cue water took longer to recover than crabs in the other groups, indicating that their motivation was lower. These findings provide clear evidence that chemical cues are a feature of these contests.