Spatial composition of pollen-mediated gene flow in sessile oak

The evolutionary consequences of gene flow are determined by its genetic composition, that is, the relative contributions of gene sources from different spatial origins and scales. In the present study we investigated multiscale pollen-mediated gene flow in sessile oak (Quercus petraea(matt.) liebl.) across the fragmented landscape of northern Germany. application of the mesoscale meteorological transport model metras+Pollen allowed us to differentiate and quantify within-stand, regional and supra-regional pollen dispersal. The simulation results were compared to the results of microsatellite-based paternity reconstructions within and between 3 oak stands. Simulations with the population-genetic model ecoGene landscape evaluated the robustness of the gene flow results to different levels of fragmentation. Within-stand gene flow dominated the reproductive system (metras+Pollen: 55% - 87%; empirical: 75% - 80%). Regional pollen sources within a focus area of 5 km x 5 km centred on the stands contributed with 9% - 40% the largest fraction of immigrant pollen. Supra-regional gene flow amounted to 5%. This general partitioning of multiscale gene flow persisted if the area of oak forest in the studied landscape was increased from 15% to 25% (10% - 36% external gene flow). In addition, reproductive connectivity between stands was not disrupted, even if the extent of oak forests was reduced to 5% (4% - 14% external gene flow). The results show that fragmented stands of sessile oak within the main part of the species’ distribution range form a reproductive network