Within-population genetic structure in Quercus robur L. and Quercus petraea (Matt.) Liebl. assessed with isozymes and microsatellites

The spatial distribution of alleles is described in a forest stand of natural origin of 5 ha comprising 355 mature Quercus petraea and Q. robur trees. Each tree was genotyped for six microsatellite loci. Previous studies on the same population based on isozymes allowed a comparison of different markers for the detection of spatial genetic structure. Different statistics were used: differentiation measures at different spatial scales, and spatial autocorrelation analysis based on Moran's index I. For microsatellites, differentiation and autocorrelation were calculated with unordered alleles (identity in state) and with alleles ordered according to their size. Results showed the same tendency of a significant, but low, spatial genetic structure for markers and different statistics. Some differences could, however, be detected. First, microsatellites interpreted as unordered alleles exhibit stronger spatial structure than isozymes or microsatellite interpreted as ordered alleles. Second, differentiation and autocorrelation values were higher in Q. petraea than in Q. robur. These differences were attributed to species differences in gene flow via pollen or seed.