Adjacent Populations of Cocksfoot (Dactylis Glomerata L.) : A detailed Study of Allozyme Variation across Contrasting Habitats

The study of gene flow between adjacent populations of cocksfoots (Dactylis glomerata L.) takes place in the plain of "La Crau" (Bouches-du-Rhône, south of France). This xeric stony land is in some places irrigated and exhibits two very different environments separated from each other only by a few meters. Using allozymes, genetic differences between cocksfoots of the two environmental types (xeric and mesic) were shown in previous works. The aim of this study was to determine the extent to which dry and moist Crau individuals were genetically differentiated, and to examine if there was any evidence that the direction and amount of gene flow was influencing the pattern of differentiation. It is firstly shown that no introgression occurs from the moist Crau towards the dry Crau populations of cocksfoot. Secondly, allelic frequencies and allelic association show that direct gene flow occurs from the dry Crau towards the moist Crau populations, but that they are very limited and restricted to places where the trees separating the two habitats are well spaced.