GENERAL VS LOCAL DIFFERENTIATION BETWEEN 2 CLOSELY-RELATED WHITE-OAK SPECIES

The geographical distribution of species differentiation throughout th e natural range of two sympatric, closely related species of oaks, Que rcus petraea (Matt) Liebl. and Quercus robur L., was investigated. By sampling species in pairs in different European regions, from Spain to Poland and Romania, the differentiation between the two species could be subdivided into general and local differentiation. Nine sequence c haracterized amplified region (SCAR) markers corresponding to genomic regions which discriminate the two species were analysed using single- strand conformation polymorphism (SSCP) or classical electrophoresis ( double-stranded DNA on agarose gel) on PCR products providing, respect ively, codominant and dominant markers. Similar levels of gene diversi ty (H-E) within the two species were observed, varying generally from 0.3 to 0.5 for dominant markers and from 0.5 to 0.86 for codominant ma rkers. SSCP loci exhibited numerous alleles that were differently invo lved in species differentiation The geographical distribution of speci es differentiation is heterogeneous between the regions, the north-eas t populations exhibiting higher differentiation than the others. For m ost led, general differentiation was higher than local differentiation and was interpreted as the result of historical causes, selection pre ssures, and intra- and interspecific gene flow.