GENE FLOW IN MAINLAND AND INSULAR POPULATIONS OF CRASSOSTREA (MOLLUSCA)

¹ The Oregon Health Sciences University, School of Medicine, Deportment of Biochemistry, 3181 S.W. Sam Jackson Park Road. Portland, Oregon 97201

Insular and mainland populations of Crassostrea species were compared with respect to relative gene flow, levels of genetic variation, and population differentiation. The relative level of gene flow was reduced among Caribbean Island subpopulations as compared to mainland subpopulations along the Atlantic seaboard and Gulf of Mexico. However, this reduction in gene flow among island subpopulations has resulted in very little population differentiation between islands or between islands and mainland demes. This suggests that the existing level of insular gene flow may adequately override genetic drift, founder effect, and weak selection. The reduction in gene flow was, however, accompanied by a substantial drop in the average heterozygosity among island demes when compared to mainland populations.