Search

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 (tm = 0.837 ± 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 (tm − ts = 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 (Fa = −0.078) was lower than that obtained for progenies (Fe = 0.089), suggesting considerable selection against selfed progenies duri...

Genetic diversity and population genetic structure of Shorea leprosula was investigated using seven natural populations distributed throughout Peninsular Malaysia and one natural population from Borneo. The mean population and species level genetic diversity were exceptionally high (He = 0.369 ± 0.025 and 0.406 ± 0.070, respectively). Heterozygosity varied among populations, ranging from 0.326 to 0.400, with the highest values found in the populations from central Peninsular Malaysia. Correlations among ecological factors (longitude, latitude, and annual rainfall) were not significant (P > 0.05), indicating that these ecological variables were not responsible for the observed genetic differences among populations. The Bangi adult population exhibited a higher level of observed heterozygosity but lower fixation indices in comparison to its seedling population. All other seedling populations also showed positive fixation indices (F), indicating a general excess of homozygotes. This also may suggest...

Starch gel electrophoresis has been carried out on leaf extracts of Shorea leprosula, S. ovalis, and Xerospermnum intermedium, rain forest trees growing in South-west Malaysia. A high level of intra-population genetic variation is indicated by electromorphic frequencies obtained from S. leprosula and X. intermedium extracts, but not so for S. ova/is extracts which yielded remarkably uniform electromorph patterns. Evidence is presented for genetic differences between age classes. IN THE TROPICAL RAIN FOREST there is a great abundance of tree species which grow close together, appear to be equivalent in their edaphic requirements, and are apparently spatially interchangeable. These features are most dramatically displayed in certain mixed dipterocarp forests of the aseasonal, wet lowlands of Malesia and thereby pose problems as to the origin of such an immense species diversity. Although spatial isolation and the abundance of normally hermaphrodite flowers in the canopy of the very tall, emergent species suggest that self-fertilization may occur, many understory species are dioecious.