Genetic diversity of a tropical tree species, Shorea leprosula Miq. (Dipterocarpaceae), in Malaysia: Implications for conservation of genetic resources and tree improvement

Genetic diversity and population genetic structure of Shorea leprosula was investigated using seven natural populations distributed throughout Peninsu lar Malaysia and one natural population from Borneo. The mean population an d species level genetic diversity were exceptionally high (H-e = 0.369 +/- 0.025 and 0.406 +/- 0.070, respectively). Heterozygosity varied among popul ations, ranging from 0.326 to 0.400, with the highest values found in the p opulations from central Peninsular Malaysia. Correlations among ecological factors (longitude, latitude, and annual rainfall) were nor significant (P > 0.05), indicating that these ecological variables were not responsible fo r the observed genetic differences among populations. The Bangi adult popul ation exhibited a higher level of observed heterozygosity but lower fixatio n indices in comparison to its seedling population. All other seedling popu lations also showed positive fixation indices (F), indicating a general exc ess of homozygotes. This also may suggest selection against homozygotes bet ween the seedling and adult stages. A low level of population differentiati on was detected (G(ST) = 0.117 with the Lambir population and GST = 0.085 w ithout the Lambir population). Furthermore, gene flow (N-m) between populat ions was nor significantly correlated with geographical distances for the p opulations within Peninsular Malaysia. Cluster analysis also did not reflec t geographical proximity and gave little insight into the generic relatedne ss of the populations. This may indicate chat the populations sampled are p arr of a continuous population with fragmentation having occurred in the re cent past.