The past ownership of a resource affects the agonistic behavior of hermit crabs

Resource value is often considered the most important nonstrategic variable in the fighting behavior of invertebrates. In our study, we tested whether the experience of shells of a given quality, occupied in the recent past, might affect the agonistic behavior of the hermit crab Pagurus longicarpus. We analyzed the fights battled by 84 test crabs against size-matched unknown rivals before (premanipulation phase) and after (postmanipulation phase) having modified the quality of the domicile shell of the contestants. Specifically, we compared the behavior of crabs that had been subject to either a worsening or an improvement in the quality of their shell with crabs that, although being similarly subject to a shell manipulation, occupied a shell of the same quality as in the premanipulation phase. We found that the crabs subject to a worsening in the quality of their shell were more aggressive than those subject to its improvement and that the former were even more aggressive than those that occupied a bad quality shell also in the premanipulation phase. Crabs seemed not to gather information about the opponent’s shell during fights or not to use this information, most often behaving in accordance with the quality of the domicile shell. These results are clear in showing the role played by the experience of a previously occupied shell, also confirming that the agonistic behavior of P. longicarpus is mainly based on decision rules of the type “own resource value dependency.”