Mating System Parameters in a Tropical Tree Species, Shorea leprosula Miq. (Dipterocarpaceae), from Malaysian Lowland Dipterocarp Forest

The mating system in a natural population of Shorea leprosula from Malaysian lowland dipterocarp forest was quantified by allozyme analysis using the multi-locus mixed-mating model. The population was found to be predominantly outcrossed (t sub(m) = 0.837 plus or minus 0.066). Variation in individual multi-locus outcrossing rates (range = 0.55-1.00) may have reflected variation in individual self-compatibility, heterogeneity in the pollen pool, differences in the mating neighborhood of individuals, or population substructure. Departure from the mixed-mating model was evident from the differences in pollen and ovule allele frequencies. Pollen pool heterogeneity and significant levels of biparental mating (t sub(m) - t sub(s) = 0.127, P < 0.01) indicated that the population was most probably genetically substructured. The inbreeding coefficient based on Wright's fixation index for maternal trees (F sub(a) = -0.078) was lower than that obtained for progenies (F sub(e) = 0.089), suggesting considerable selection against selfed progenies during growth of seedlings to reproductive size. Incidence of multiple seedlings was observed in a small proportion of seeds, but genetic analysis and genotype comparisons showed that this was not due to apomixis and may have been caused by multiple fertilization.