Distant gene flow in tropical trees

Canopy trees, the main structural elements of tropical rain forests, typically occur at the density of one adult or less per hectare. Because these trees are strongly outcrossed, their populations are expected to cover large areas of hundreds of square kilometres. These large populations are now being fragmented by deforestation and habitat alteration, but the genetic consequences of fragmentation remain largely unexplored because of the lack of information about effective population sizes and gene flow in canopy trees. We have recently succeeded in isolating a relatively new class of genetic markers, simple sequence repeats (SSRs), in tropical trees and have demonstrated their use in addressing centra issues in conservation biology. Here, we demonstrate the use of these markers in estimating gene flow and mating parameters in Pithecellobium elegans, a large canopy tree from central American rain forests. Our measurement of the distance of pollen flow is among the largest, and exclusion probabilities for assigning paternity the highest reported for any natural population of plant species. Furthermore, our methods allow us to assign paternity to almost any seed collected from the population.