Patterns of gene flow inferred from genetic distances in the Mediterraneanregion

The analysis of population structure may lead to inferences about demograph ic phenomena. In particular, regions of sharp genetic differentiation sugge st the existence of factors that impaired gene flow and increased the evolu tionary role of genetic drift. Hen, we present an analysis of a data set of 10 allele frequencies in 39 populations of the Mediterranean region. As a preliminary step, we describe spatial patterns of allele frequencies using spatial autocorrelation analysis. We then construct a network connecting lo calities and estimate genetic distances along the edges of the network. By applying specific algorithms, we locate on the map the areas of sharpest ge netic differentiation, or genetic boundaries. The main boundaries separate the northern and the southern coasts, especially in their western portions; in addition, several localities appear genetically isolated. The comparati vely high genetic differentiation across the western Mediterranean, where t he sea distances between localities are shorter, strongly suggests that the sea distance by itself can hardly be regarded as a major isolating factor among these populations. On the contrary, the decrease in genetic resemblan ce between populations of the 2 coasts as one proceeds westward may reflect an increased genetic exchange in the eastern Mediterranean basin or indepe ndent human dispersal along the 2 coasts or both.