Abstract
Abstract: We tested five hypotheses regarding the behavior of hermit crab pairs(an attacker and a defender)fighting for shells. The hypotheses are(1)an attacker's decision to escalate a fight will vary depending on the defender's sex, (2)the attacker more often escalates the fight if it would gain a better quality of shell after the shell exchange, (3)the attacker less frequently escalates the fight the closer its shell is to its preferred size, (4)the value of shells larger or smaller than the preferred size is not equal for attackers, and(5)the trend in hypothesis(4)differs between sexes. In the laboratory we observed the occurrence of shell rapping (an indicator of fight escalation)by attackers under various shell conditions. Although the first three hypotheses were not supported, the final two were supported by the results that female attackers more often rapped against the defender when the attackers occupy shells larger than their preferred size. These results indicate that attackers do not assess precisely cost-benefit with defender's shell but rather are more willing to fight only if their own shell quality is lower than a threshold irrespective of the improvement in shell quality after the shell exchange.
