Shell morphologies of bay scallops, Argopecten irradians, from extant and prehistoric populations from the Florida Gulf Coast: Implications for the biology of past and present metapopulations

Genetically conservative changes in a bivalve population may be mirrored by morphological changes in the shells of individuals in that population. The rate of such evolutionary change is usually so slow that the changes in sh ell morphology cannot be detected in short-term studies of local population s. When selective pressure becomes severe, however, the magnitude of the ge netic changes may be intensified, and thus the magnitude of the morphologic al changes in the shells may be greater--and more detectable. We compared t he morphometric features of specimens from from archaeological sites with t hose from geographically coherent modern collections to determine if such d etectable morphological changes have taken place in the populations studied . Analyses of bay scallop shells (Argopecten irradians) from nine modern po pulation spanning Florida's entire Gulf coast and from four archaeological sites located from central to southern Florida reveal that major morphologi cal shifts in the shells of two local populations have occurred sometime in the past 500 to 1500 years. These shifts may have implications regarding t he persistence of the scallop metapopulations and the efficacy of future ef forts to conserve the species.