Sexual differences in the shell assessment behavior of the hermit crab <i>Pagurus filholi </i>(Decapoda: Anomura: Paguridae)

Abstract

Sexual differences in shell exploitation behavior of the hermit crab Pagurus filholi were investigated in the laboratory. Prior to this study, the size of shells preferred by crabs of a given size was estimated by free-shell choice experiments and was used for the present experiment. Crabs collected from the field were removed from their original shells and put in Littorina brevicula shells smaller or larger than preferred, or in shells with preferred size. Each of crabs was put in an aquarium provided with 100 L. brevicula shells, and, to maintain the motivational state of crabs constant during the experiments, the aperture of each shell was blocked by glass balls to prevent crabs from exchanging shells. We counted the number and size of shells assessed by each crab. Results were that females more frequently assessed shells than males did during the observation time, and were not affected by the difference in size adequacy of their occupying shell. The sizes of shells explored by females were similar to their preferred size, however, males tended to assess shells that were larger than preferred. This sexual difference was not affected by size of their original occupying shells. The female's higher activity in shell exploitation behavior and their better shell size suitability in the field suggested that acquirement of empty shells , for which opportunity is rare in the field, could be an important process for improving their shell size suitability in the field.