A genetic basis for geographic variation in shell morphology in the bay scallop, Argopecten irradians

The bay scallop, Argopecten irradians, exhibits extensive variation in morphology among geographically separated populations, resulting in the recognition of three major subspecies (A. i. irradians, A. i. concentricus, A. i. amplicostatus). The extent to which morphological variation results from differing environmental conditions is unknown. In the present study, bay scallops from Massachusetts, North Carolina, Florida, and Texas were collected, spawned and the offspring reared in a common garden experiment to determine if scallops cultured under similar environmental conditions exhibited the morphology expected given the geographic origin of their parents. Significant differences among populations were indicated by ANOVA in both the wild-caught (13/14 morphological characters) and cultured (11/14 characters) scallops. Principal components analysis clustered wild-caught scallops according to geographic origin and cultured scallops according to geographic ancestry. The morphological characters most influential in resolving groups were plical width, plical spacing, number of plicae and valve convexity. Geographic variation in morphology apparently has a strong genetic basis, and reflects significant differentiation among disjunct populations of bay scallops. Received: 12 September 1996 / Accepted: 15 October 1996