GEOGRAPHICAL STRUCTURE OF GENE DIVERSITY IN QUERCUS-PETRAEA (MATT) LIEBL .2. MULTILOCUS PATTERNS OF VARIATION

Two-locus composite disequilibria were estimated for all 28 pairs of l oci (from eight loci) in 81 populations of Quercus petraea spread over the natural distribution of the species. Significant disequilibria we re found in almost all populations for two pairs (Aap-A/Lap-A, Mr-A/Di a-A) that have also shown strong linkage in cosegregation analysis. Th ese pairs belong to the so-called complex loci producing nearly identi cal gene products and that are tightly linked. Significant disequilibr ia were also found for other pairs of loci that are linked to a smalle r degree. The amount of disequilibrium followed a geographical pattern . The number of pairs showing significant disequilibria per population was higher on the edges of the natural range (Norway, Great Britain, Turkey). Disequilibria for the two pairs (Aap-A/Lap-A, Mr-A/Dia-A) wer e also higher at the edges of the distribution and were correlated wit h longitude. Population differentiation resulting from the association s of alleles at different loci was increased when the correlations of allele frequencies at the within- and between-population level were of different magnitude. It is suspected that correlations at the between -population level may arise from historical causes rather than gametic disequilibrium. Finally, the first canonical variate (multivariate sc ore) including allelic frequencies of all eight loci fellows a strong longitudinal pattern of variation.