Nucleotide variation in the GapC region of four species of Shorea and their putative hybrids

Very little is known about the levels and patterns of DNA polymorphism in populations of tropical trees. In this study, we investigated population genetic structure of the four following Shorea species: Shorea acuminata, S. curtisii, S. leprosula and S. parvifolia from peninsular Malaysia using DNA sequences of Glyceraldehyde-3-phosphate dehydrogenase nuclear gene (GapC). The average nucleotide diversities of the investigated species for silent sites (πsil= 0.0027) were lower than those reported for herbaceous plants, and similar or somewhat lower than those of other woody species. These low levels of nucleotide diversities may be caused by small effective population size of Shorea species. We found that some individuals harbored atypical haplotypes consisting of sequences from two different species. The segmented architecture of these haplotypes suggests past inter-specific gene exchange and fertility of the hybrids. As demonstrated in this study analysis of DNA sequences provides genetic evidence for the occurrence of inter-specific hybridization and gives important insights into its evolutionary effects.