Phenotypic and genotypic population differentiation in the bivalve mollusc Arctica islandica: Results from RAPD analysis

The bivalve mollusc Arctica islandica is an important commercial species with a presumed panmictic dispersal strategy, and is widely distributed throughout much of the soft sediment benthos of the North Atlantic continental shelf. Previous studies have shown that there can be gross morphological differences between populations, which has led to the suggestion that this may be reflected in genotype. So far, only one study has examined the population genetics of this species, revealing, depending upon location, that populations are only genetically distinct at a macroscale (>1000 km), thereby supporting the assumption of panmixia. Examination of the quantitative morphological traits between 5 different populations (4 North Sea and 1 Canadian) determined that all populations could be readily identified from their unique morphologies (shapes/growth patterns) derived from 2 factors resulting from a principal components analysis. Investigation, using random amplified polymorphic DNA (RAPD) analysis, into the genetics of the populations, to indirectly assess whether the observed phenotypic differences could be related to potential differences in genotype, revealed that all populations were genetically distinct (between populations overall phi_ST = 0.662) from each other even at a microscale (<25 km) (phi_ST = 0.719). However, no correlation between genetic distance, morphological distance and/or geographical distance, whatever metric was applied, could be obtained. It is concluded that although phenotypic differences can be used to distinguish between populations of A. islandica, it should not and cannot be used to infer genetic differences in the absence of further studies. What is interesting is that the results from the genetic analysis dispute the presumption that the dispersal patterns of A. islandica is in any shape or form panmictic. This has very important consequences for the management of the species. The results are discussed with reference to the possible mechanisms responsible for maintaining a high degree of genetic diversity between the populations that were studied.