Aurora kinases

to relinquish its shell, allowing the attacker to evict it by pulling it out through the aperture; or the attacker may give up, and release the defender, without effecting an eviction. If the attacker is successful, it will perform the usual investigatory activities on the vacated shell and decide whether to occupy it permanently. During this process the evicted defender is left without a shell, but once the attacker has made its decision the defender is free to move into the shell that is eventually discarded, such that the encounter often ends with an 'exchange' of shells. Negotiation or aggression? In P. bernhardus, successful attackers rap more vigorously than those that give up, performing more raps per bout, hitting harder and leaving shorter pauses between bouts. The detail of shell rapping has not been examined in other species but in all cases there is the possibility that the defender, as well as the attacker, can benefit from the encounter. For example, if a defender entered the encounter with a shell that was much too large and exchanged it for a smaller shell that the attacker discarded, then the exchange could lead to an improvement in the defender's shell quality as well as that of the attacker. Indeed, it has been shown in C. vittatus that exchanges are more likely to occur if the defender also benefits. It has been suggested that these hermit crabs 'negotiate' rather than 'fight' over their shells, and that the function of shell rapping is in fact to advertise the quality of the attacker's shell, allowing the defender to base its decision on this factor. The defender could assess this by monitoring the pitch of the raps, which would vary with shell size. But this doesn't explain the difference in vigour between evictions and non-evictions in P. bernhardus. If the rapping advertises shell quality why would attackers need to rap vigorously as shell quality will not vary with the vigour of rapping? In P. bernhardus at least, shell exchanges seem to be primarily agonistic encounters where any benefit to the defender is incidental to the gains made by a successful attacker. Shell rapping seems to be related to the attacker's stamina and advertises its fighting ability or 'resource holding potential'. What can hermit crabs tell us about decision-making and contests? Theoretical models of fighting are based on the idea that animals gather information about the resource, …