In situ and Ex situ Conservation of Commercial Tropical Trees - ITTO

319ratios that deviated from Hardy-Weinberg estimation due to a lack ofheterozygotes.Fixation indexHigh homozygosity was observed from positive fixation indices in seedlingsamples that may have been produced through selfing or half-sib mating. Thishad also been shown through a study on Pinus sp. (Muona 1989). Accordingto Muona (1989), positive fixation indices at the seedling level might be due toself-pollination. Seedlings produced through inbreeding usually die off beforematurity as they are weaker. This follows the theory of natural selection, whichstates that selection is the dominant force in evolution (Hartl 1980). Excess ofheterozygosity in locus Shc02 as shown by a negative value might mean thatthis locus responds to selection pressure and may be linked to adaptive traits.The Wahlund Effect (1928) states that natural populations that aredivided into sub-populations might have allele frequencies that deviate frompopulations due to natural selection, or random genetic drift in the case of smallpopulations. The effect is that the homozygous genotype frequency of the wholepopulation exceeds Hardy-Weinberg equilibrium, whereas heterozygotes of thewhole population decrease from the Hardy-Weinberg ratio. In the case of D.aromatica, it could be said that all the populations in Peninsular Malaysiaoriginated from one large population that had been sub-divided into a few subpopulations.This would explain the high fixation indices observed in all D.aromatica populations.Genetic diversity in D. aromatica populationsOn the whole, the five populations showed a high level of genetic diversity. Outof the seven microsatellite loci studied, 40 alleles were observed, which is amean of 5.14 ± 0.20 alleles per locus. This value is higher than those obtainedfrom isozyme markers for conifers (2.29) and tropical species (2.02) (Hamrickand Loveless 1989). D. aromatica, using isozyme markers, gave a value of 4.1(Lee et al. 2000b). Generally, microsatellite markers yield a high number ofalleles per locus due to length mutations that causes differences in repeat units.Amos et al. (1993) obtained 54 alleles from one whale microsatellite locus andFornage et al. (1992) obtained 15 alleles in one locus located on the first intronof the C-II apoliprotein gene in a French human population.Expected heterozygosity was more than the observed value by 0.218,showing an excess of homozygotes. This may be because leaf samples ofseedlings were used in this study. Expected heterozygosity (H e= 0.709) was