Genetic diversity and outcrossing rate between undisturbed and selectively logged forests of Shorea curtisii (Dipterocarpaceae) using microsatellite DNA analysis

To evaluate the effect of flowering tree density on genetic variation in a dominant tree species, genetic diversities and outcrossing rates of Shorea curtisii (Dipterocarpaceae) were compared between undisturbed and selectively logged forests using microsatellite markers. The mean heterozygosity and the effective number of alleles per locus in the selectively logged plot were not significantly different from those of the undisturbed plot. However, the average number of alleles derived from the pollen donor was significantly lower in the selectively logged forests, indicating the possibility of a loss of genetic variation in future generations. The average outcrossing rate for 11 trees in an undisturbed plot was 96.3%, which was similar to other reports from dipterocarp species based on isozyme analysis. However, the outcrossing rate in the selectively logged plot was 52.2% for five trees, which was significantly lower than that in the undisturbed plot. This decline of outcrossing rate in the selectively logged plot may result from the much lower density of conspecific flowering trees, and the high rate of selfing may result in inbreeding depression and/or a decrease in genetic variation of this forest in future generations.