INTRASPECIFIC GENETIC-STRUCTURE IN A MIXED POPULATION OF QUERCUS-PETRAEA (MATT) LEIBL AND QUERCUS-ROBUR L

The intraspecific genetic structure of a mixed population of sessile a nd pedunculate oak was studied in the Petite Charnie Forest, Sarthe, F rance, using enzyme electrophoresis. Spatial structure was analysed by calculating F-statistics and autocorrelations at different scales of spatial subdivision of the population. F-statistics were also used to compare the genetic structure of groups of trees subdivided according to the phenology of flowering. Spatial organization of phenology of fl owering was studied with autocorrelation methods. In both species, a h ighly significant heterozygote deficiency was found at the population level. Spatial genetic structure was at least partially responsible fo r this deficiency, as demonstrated by the variations observed in F-sta tistics in relation to the size of this population subdivision. The si gnificance of the observed structure was confirmed by comparison with a null hypothesis generated with the help of permutation analysis. We suggest that the limited dispersal of pollen and/or seeds in the stand gave rise to a family structure. The autocorrelation in phenology of flowering found in both species could contribute to lower the neighbou rhood size and then to increase the Wahlund effect. Autocorrelation an alyses allowed us to show that heterogeneity of patterns of structure among loci was present. Other possible causes of the genetic structure and its heterogeneity are discussed.