Geographic structure of chloroplast DNA polymorphisms in European oaks.

Chloroplast DNA polymorphisms have been detected by the conventional Southern-blotting hybridization method in four species of European oaks (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica). Three polymorphisms, shared by at least three of these species, can be scored directly in ethidium bromidestained gels and were used in a broad survey of the level of differentiation of the oak species and of their pattern of genetic structure in western Europe. The highly significant geographic variation and the high genetic differentiation (Gst=0.895, SGst=0.025) indicate a low level of cytoplasmic gene flow. We conclude that cytoplasmic genomes are well suited for the reconstruction of past migrational routes of such a complex of species.