Postpollination Mechanisms and Relative Fitness Contribution of Differential Outcrossing Distance

Research will focus on characterizing which individuals share parentage of the seeds that form the next generation. By studying mating systems of two species that are representative of non-woody perennial plants, the investigators will test the idea that the best mating for a plant will depend on the physical proximity of mates, because this reflects genetic similarity. Previous research has indicated that crossing success should be highest between plants separated by an intermediate distance, and thus neither too similar nor too dissimilar genetically. A major goal of this research is to obtain complete lifetime estimates of seedling survival and reproduction in order to test the hypothesis that offspring from the 'optimal outcrossing distance' are most fit. A second goal is to assess how great the fitness differences are by using a complex kind of experimental pollination. A third goal is to assess fitness costs associated with germinations at various distances from parental plants. A fourth goal is to see whether 'postpollination' selection will bring the actual mating system into closer agreement with the optimal mating system. These studies have implications for other plants, including crop species. It seems likely in general that fitness will be sensitive to genetic similarity of mates on a finer scale than hitherto recognized, and that postpollination selection will modify the outcome. This research will provide a closer investigation of these possibilities.