Phenotypic plasticity in the life history of the mangrove snail Cerithidea scalariformis

Although phenotypic variation is commonly observed an-tong populations, the relative contribution of genetic and environmental conditions to phenotypic expression, including life history traits, is often unresolved. We measured characteristics of several isolated populations of the mangrove snail Cerithidea scalariformis across 2 habitat regimes (exposed marsh and forested mangrove marsh) and found considerable variation in all population characteristics over a 2 yr period. Differences existed among populations in density and individual size, and snails in the forested marsh were significantly larger than those in the exposed marsh. In a reciprocal transplant experiment, we tested the extent to which phenotypic plasticity may contribute to observed population differences in size and several other attributes. Regardless of source, snails maintained in the exposed marsh exhibited faster growth, earlier maturation, greater size, and higher rates of parasitism than snails in the forested marsh. Our results demonstrate that considerable plasticity in demographic traits exists in C. scalariformis across the highly variable range of conditions in coastal wetland habitats. The proximate and ultimate cause of plasticity in these snails, as well as any associated advantages, remain to be tested.