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

Abstract

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 shell morphology cannot be detected in short-term studies of local populations. When selective pressure becomes severe, however, the magnitude of the genetic changes may be intensified, and thus the magnitude of the morphological changes in the shells may be greater—and more detectable. We compared the morphometric features of specimens from archaeological sites with those from geographically coherent modern collections to determine if such detectable morphological changes have taken place in the populations studied. Analyses of bay scallop shells (Argopecten irradians) from nine modern populations spanning Florida's entire Gulf coast and from four archaeological sites located from central to southern Florida reveal that major morphological shifts in the shells of two local populations have occurred sometime in the past 500 to 1500 years. These shifts may have implications regarding the persistence of the scallop metapopulations and the efficacy of future efforts to conserve the species.