To rap or not to rap: Do hermit crabs assess the impacts of shell rapping on their opponents?

Hermit crabs are known to participate in non-injurious fights over the ownership of gastropod shells. Bouts of fighting are considered successful if an exchange of shells occurs after a period of shell rapping. Shell rapping involves the attacking crab bringing its shell rapidly and repeatedly into contact with the shell of the defending crab in a series of bouts. Many studies have investigated how the repeated pattern of shell rapping may convey information about the relative resource holding potential (RHP) of the attacker to the defender and also the attacker’s motivation to win the fight. However, no studies to date have investigated whether attacking hermit crabs can assess the impacts their own shell rapping activities are having on the defending opponent. Therefore, the present study aimed to determine whether attacking Pagurus bernhardus hermit crabs assessed the effectiveness of shell rapping at causing the eviction of the defending crab. This was achieved by rubberising the surface of the defending crab’s shell so that the impacts of shell rapping were dampened. The subsequent behaviour of attacking crabs was then analysed to determine if attackers were altering their behaviour to win the contest based on the information gathered regarding how successful shell rapping was at causing the defender to give up the fight. The results of this study indicate that attackers may assess the impacts of rapping on their opponents. The results overall, however, were inconclusive as the changes in behaviour and the pattern of rapping by the attacking crab may also have occurred due to a loss in motivation or fatigue. Suggestions for further work include analysing the startle response times and lactate concentrations of the attacking crabs at various 4 intervals throughout the fight to determine if losses of motivation or fatigue are the most likely explanation as to why attackers change their behaviour.Faculty of scienc