Low inbreeding and high pollen dispersal distances in populations of two Amazonian forest tree species

Recent studies suggest that tropical tree species exhibit low inbreeding and high gene dispersal levels despite the typically low density of conspecifics in tropical forests. To examine this, we undertook a study of pollen gene dispersal and mating system of two Amazonian tree species. We analyzed 341 seeds from 33 trees at four microsatellite loci in a Carapa guianensis population from Brazil, and 212 seeds from 22 trees at four microsatellite loci in a Sextonia rubra population from French Guiana. Differentiation of allele frequencies among the pollen pool of individual trees was Phi(FT) = 0.053 (95% CI: 0.027-0.074) for C. guianensis and Phi(FT) = 0.064 (95% CI: 0.017-0.088) for S. rubra. The mean pollen dispersal distances were estimated at 69-355 m for C. guianensis, and 86-303 m for S. rubra, depending on the pollen dispersal model and the estimate of reproductive tree density used. The multi-locus outcrossing rate was estimated at 0.918 and 0.945, and the correlation of paternity at 0.089 and 0.096, for C. guianensis and S. rubra, respectively, while no significant levels of biparental inbreeding were detected. Comparing trees with high and low local density of conspecifics, we found no evidence for differences in inbreeding levels. The results are discussed within the framework of the emerging picture of the reproductive biology of tropical forest trees.