XVI International Botanical Congess

Several recent empirical and experimental studies of hybrid zones involving a diploid and a polyploid taxa suggest the evolution of premating isolating mechanisms between ploidy levels in contact zones. Here I present some results obtained in a hybrid zone between a diploid grass (Anthoxanthum alpinum) and its autotetraploid derivative. The purpose of this study was to compare selection forcesacting on flowering phenology in diploid and tetraploid populations both in pure and mixed situations.The flowering phenology and reproductive success of plants were recorded in 10 different populations over three years. In the first two years of study, I found evidence for directional selection acting in opposite directions on the phenology of the two ploidy levels in the mixed population. In contrast, I found no evidence of selection on phenology in pure populations.