DIRECT AND INDIRECT ESTIMATES OF SEED VERSUS POLLEN MOVEMENT WITHIN APOPULATION OF PONDEROSA PINE

We examined the spatial distribution of maternally inherited mitochond rial DNA and paternally inherited chloroplast DNA polymorphisms in a p ermanently marked stand of ponderosa pine (Pinus ponderosa Laws). Move ment of maternally inherited mtDNA occurs only via seed dispersal, and mtDNA haplotypes showed significant patch structure. Moreover, indivi duals within patches identified by mtDNA haplotypes were related appro ximately as half-sibs based upon analysis of allozyme genotypes. Thus, seed dispersal is limited within the population, and creates matrilin eal clusters in space. By contrast, paternally inherited cpDNA is disp ersed by movement of both seed and pollen. Chloroplast DNA polymorphis ms showed no evidence of patch structure, but rather a weak (and nonsi gnificant) trend toward hyperdispersion, suggesting nearly unlimited m ovement of pollen among trees within this stand. Two of the trees had unique allozyme alleles, which were used to directly measure pollen mo vement away from those trees. Marked pollen was as likely to disperse across the population as it was to fertilize near neighbors.