The evolutionary causes of genetic differentiation in natural plant populations are poorly understood. Estimates of gene flow are necessary to distinguish the relative roles of selection and random genetic drift in producing population structure. The purpose of the proposed research is to estimate the contributions of gene flow, the mating system and selection to population genetic differentiation in the marine angiosperm, Zostera marina L (eelgrass). Preliminary data suggests that eelgrass populations are genetically differentiated, despite the potential for long distance dispersal and high turnover rates of colonization patches in the marine environment. Estimates of the effective population size, the mating system and the contribution of adult migration to realized gene flow will be incorporated into existing predictive models of genetic differentiation. The possibility that genetic drift contributes to observed population structure will be evaluated by 1) estimates of the spatial scale over which gene flow occurs, and 2) transplant experiments designed to detest spatially varying selection. Information gained from this study will be used to evaluate the generality of tends regarding pollination systems, gene flow and population genetic structure established in terrestrial systems.
