The way in which plant species exchange pollen during mating determines which individuals make a genetic contribution to the next generation. This breeding structure thus effects levels of genetic variation and potential patterns of evolutionary change in the population. Dr. Loveless will examine how different individuals sample the pool of available pollen from their neighbors and the effects of this mating system on progeny genotypes. The study species, Tachigali versicolor (a legume) is especially interesting because it is outcrossed. The progeny of different fruiting trees are thus likely to have sampled pollen from conspecific individuals in the immediate vicinity of the seed parent. This permits Dr. Loveless to isolate and measure the effects of the spatial population structure on mating systems, and to assess the amount of variation in the mating system among individuals flowering in a single season. The tree is also monocarpic; each individual flowers once and dies. The presence of known and aged cohorts of seedlings in the forest on Barro Colorado Island, Panama, will allow assessment of particular elements of the reproductive biology of this species which result from spatial and phenological structure in the adult population. The results of this work should have bearing on understanding of the processes by which genetic diversity is generated and maintained in tropical plant populations, and on the ecological processes by which pollen is moved about in rain forest communities. The data should also contribute in a general way to theories of plant mating systems which are applicable to both temperate and tropical plant species, and should be important in plant breeding and in understanding microevolutionary processes in natural communities. Such information is important in tree breeding programs to measure the degree of isolation required and the range over which pollen might be transported. It also impacts efforts to assess minimum critical population sizes for canopy rain forest tree species, based on breeding biology of the species.
