VARIATION OF CHELIPED ALLOMETRY IN A HERMIT CRAB: THE ROLE OF INTRODUCED PERIWINKLE SHELLS

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Abstract
From Connecticut to Massachusetts, Pagurus longicarpus hermit crabs commonly inhabit shells of the introduced periwinkle snail, Littorina littorea. South of Connecticut, these periwinkles are rare and thus their shells are seldom inhabited. For male P. longicarpus along the Atlantic coast, use of periwinkle shells does not correlate with geographic differences in carapace length, but does correlate with geographic differences in cheliped allometry. Further, geographic patterns of shell use may indicate that periwinkle shells increased the shells available to P. longicarpus in New England. Such an increase in shell availability is associated with reduced relative cheliped growth in laboratory populations and may be responsible for the correlation between use of L. littorea shells and reduced right cheliped allometry in field populations. Museum specimens of male P. longicarpus from pre-L. littorea Connecticut also show significantly faster relative growth of the right cheliped than modern crabs.