No abstract

Large-scale genetic structure revealed in tree populations in SE Asia, as well as in many temperate forests, has been shaped by climatic fluctuation in the late Pleistocene, most importantly by that in the last glacial period. In a comparative study of the phylogeographic patterns of two closely related dipterocarp species, Dryobalanops aromatica C.F.Gaertn. and D. beccarii Dyer, we investigated how changes in land area associated with changes in climate affected large-scale genetic structure. We examined the genetic variation of D. aromatica, collected from nine populations throughout the Sundaic region, and of D. beccarii, collected from 16 populations mainly in Borneo, using seven polymorphic microsatellite markers. The two species were clearly distinguishable in the STRUCTURE analysis, although hybridisation probably occurred in sympatric populations and also in several other populations. The D. aromatica populations were divided into two main groups by the STRUCTURE analysis: Malay–Sumatra and Borneo. Mixing of the Sumatra and Borneo clusters occurred on the Malay Peninsula, supporting the hypothesis that tropical rainforests expanded over a dried Sunda Shelf during the last glacial period. The two main genetic clusters might have been formed by repeated cycles of fluctuation in land area. The D. beccarii populations in Borneo were divided into four geographically distinct groups: western Sarawak, central inland Sarawak, central coastal Sarawak and Sabah. The population on the Malay Peninsula (Gunung Panti) was an admixture of the four Bornean clusters. This suggests that this population is a relic of the recent range expansion of D. beccarii during the last glacial period.

The genus Dryobalanops Gaertn. f. is a small but important genus that contains seven species and is found in the Southeast Asian tropical rain forests. Seven polymorphic nuclear microsatellite markers were analyzed in 46 natural populations of six extant Dryobalanops species (N = 700 individuals) covering the distribution range in Western Malesia. The mean gene diversity at the species level ranged from 0.392 in D. rappa to 0.635 in D. aromatica. The F ST value ranged from 0.156 in D. keithii to 0.283 in D. beccarii and all F ST values were highly significantly greater than zero. These results suggest that gene flow between populations has been limited and intensive genetic drift has occurred in all of the species. Plants with narrowly distributed species such as D. keithii and D. rappa, which are endemic to Borneo, tend to have lower levels of genetic diversity compared with widespread species such as D. aromatica. STRUCTURE analysis revealed that at least two of the six species could be effectively discriminated each other. The results of this study will be helpful for building effective conservation schemes as well as for providing basic data for future provenance trials of Dryobalanops species.

No abstract

Diel carbohydrate dynamics were studied on a canopy-layer species of Hydnocarpus ilicifulius in Dry Evergreen Forest (DEF) in Thailand. The measurement was conducted in the beginning of dry season in1997. Leaves, twigs, stems and roots were sampled every 3 hours during a 24-hours period, and contents of sucrose, hexose and starch in all tissues were quantified. The fluctuations of total nonstructural carbohydrate (TNC) content in every organ seemed to have a baseline with a few peaks on the line.The minimum values of TNC contents in all organs were around 1.00 mg gt of DW and they suggested a "baseline" of the fluctuation. The baseline would define a long-term carbohydrate storage in the organ and the peak showed the temporary increment. The peaks occurred at 3 to t hours later from the peak oforgans immediately above. The different peak occurrences seemed to reflect the mass carbohydrate movement because the time difference in the peaks reasonably fit with the reported value of tranSlocation rate. The ranges of diel fluctuations were equivalent to that of the seasonal change reported in the past. It was suggested that studies of carbohydrate contents in plants should take this large variation into consideration.