THE EFFECTS OF SHELL SIZE AND SHAPE ON GROWTH AND FORM IN THE HERMIT CRABPAGURUS LONGICARPUS

Abstract

Pagurus longicarpus from two geographic locations were raised in the same environment in three species of gastropod shell. These shell species differed in shape and maximum size. Crabs in small, high-spired shells attained smaller sizes than those in large, low-spired shells. Further, the relative growth rates of male crabs showed differences related to shell differences. Males in small, high-spired shells produced relatively longer claws and greater right/left claw asymmetry than males in large, low-spired shells. These results show the close interaction between hermit crabs and utilized shells and may explain the geographic variation of P. longicarpus. Along the Atlantic coast, southern crabs are smaller and have relatively longer claws and greater right/left claw asymmetry than northern crabs. Southern crabs utilize small, high-spired shells almost entirely, whereas northern crabs utilize a high proportion of large, low-spired shells. Size and shape differences between geographic populations of P. longicarpus thus may be due to differences in inhabited shells.