This project aims at understanding the relation between neutral population structure and local adaptation in a marine fish. This is done by studying the interaction between selection, population history, gene flow and genetic drift. To study adaptation of a species a sound knowledge on the spatio/temporal genetic structure is a prerequisite. The relative importance of genetic drift and gene flow in the sand goby will be estimated from a spatio-temporal population genetic analysis with various kinds of neutral genetic markers. Only than is it feasible to show and quantify local adaptation over an ecological gradient and to link the distribution of adaptive variation with neutral structure. In this way the relative importance of adaptation can be estimated and partially explained. This will be done with indirect methods, outlier loci (genome screening) and possible indications of selection (candidate gene analysis).