POPULATION-GENETICS OF CORDIA-ALLIODORA (BORAGINACEAE), A NEOTROPICAL TREE .3. GENE FLOW, NEIGHBORHOOD, AND POPULATION SUBSTRUCTURE

The utility of a) rare allozyme markers and b) paternity exclusion in estimating gene dispersal in tropical forest trees was demonstrated for a population of Cordia alliodora (R. and P.) Oken in Costa Rica. Based on the number of alleles in common, near neighbors were more highly related genetically than were more distant trees. The spatial clustering of relatives was within 50 m, coinciding to a large extent with the seed dispersal curve. Most pollen originated from within 75 m of the mother tree, although a low but substantial proportion of pollen movement was from as far as 280 m. Overall gene flow was extensive, with neighborhood areas as large as 7 ha. Neighborhood sizes at any moment in time and space were, however, relatively small, such that overall variation is maintained by continuous gene flow between neighborhoods. The results indicate that deforestation and fragmentation could curtail such gene how leading to an erosion of genetic variation within fragments.