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 t he recognition of three major subspecies (A. i. irradians, A. i. conce ntricus, A. i. amplicostatus). The extent to which morphological varia tion results from differing environmental conditions is unknown. In th e present study, bay seal lops from Massachusetts, North Carolina, Flo rida, and Texas were collected, spawned and the offspring reared in a common garden experiment to determine if scallops cultured under simil ar environmental conditions exhibited the morphology expected given th e geographic origin of their parents. Significant differences among po pulations were indicated by ANOVA in both the wild-caught (13/14 morph ological characters) and cultured (11/14 characters) scallops. Princip al components analysis clustered wild-caught scallops according to geo graphic origin and cultured scallops according to geographic ancestry. The morphological characters most influential in resolving groups wer e plical width, plical spacing, number of plicae and valve convexity. Geographic variation in morphology apparently has a strong genetic bas is, and reflects significant differentiation among disjunct population s of bay scallops.