Blackstone, N. W. 1985. The effects of shell size and shape on growth and form in the hermit crab Pagurus longicarpus. Biological Bulletin 168:75-90.

Geographically separated hermit crabs of a given species have been shown to differ markedly in terms of morphological characteristics. Regional variation in the types of available gastropod shells has been suggested as the cause of this observed variation in body form. Is the body form of growing hermit crabs influenced by the size and shape of gastropod shell inhabited?

Pagurus longicarpus along the Atlantic coast of North America exhibit north-south variation in overall size and degree of right-left asymmetry. Individuals from southern regions are typically smaller and more asymmetrical (as measured by size difference between left and right chela) than those found in northern regions. This trend toward smaller size and greater asymmetry correlates with an increased utilization of smaller, more highly-coiled gastropod shells among P. longicarpus in southern regions.

Blackstone raised P. longicapus in gastropod shells of species differing in overall size and the extent to which the shells were coiled. Hermit crabs raised in smaller and more highly-coiled shells did not grow as large as crabs in large, less coiled shells. However, the degree of asymmetry was greater in hermit crabs raised in small, highly-coiled shells.

Blackstone concludes that hermit crab morphology is determined by the properties of the shell inhabited during growth. The results suggest size and symmetry of growing individual hermit crabs gradually changes to conform with the size and symmetry of the gastropod shell. Such a high degree of phenotypic plasticity would allow dispersal to environments with gastropod species of different shell morphologies.

(248 words)

Back to Zool 250 Home Page
(posted May. 1 2005)