龙脑香科植物望天树的居群遗传结构及分化

Population Genetic Structure and Differentiaton of Parashorea chinensis (Dipterocarpaceae)

运用“水平切片淀粉凝胶电泳等位酶分析”方法 ,对国家一级珍稀濒危保护植物望天树 (Parashoreachinensis)进行了遗传多样性和居群分化的研究 ;通过对分布于滇南、滇东南和桂西南的 9个天然居群 (中国科学院西双版纳热带植物园引种栽培的 2个人工居群作为对照 ) ,11个酶系统 16个等位酶位点的研究表明 ,望天树群体内遗传变异水平极低 ,多态位点比率P为 6 2 5 %～ 12 5 0 % (平均为 6 82 % ) ,等位基因平均数A为 1 0 6～ 1 13(平均为 1 0 7) ,平均期望杂合度He为 0 0 32～ 0 0 5 4 (平均为 0 .0 35 ) ,平均观测杂合度Ho为 0 0 6 3。所有居群Pgm - 1位点的基因型均为杂合体 ,其余位点的基因型均为纯合体。居群间存在低水平的遗传分化 ,GST值为 0 0 30 ,结果明显不同于其它热带植物的报道。望天树群体的遗传结构单一 ,一方面反映了群体内存在大量内繁育 (无融合生殖、近交 ) ,另一方面也说明了在进化过程中该种曾经历了严重的瓶颈效应 ,遗传变异大量丧失。

The genetic diversity and population differentiation of Parashorea chinensis, a rare and endangered dipterocarp, and listed in the Plant Red Book under Grade I, were examined using allozyme analysis of horizontal sliceable starch gel electrophoresis. Considering its narrow distribution, which was limited in the South & Southeast of Yunnan and Southwest of Guangxi, allozyme data for 16 loci of 11 enzymes in 9 natural populations (as a comparison, two cultivated populations in Xishuangbanna Tropical Botanical Garden were analyzed) indicated extremely low level of genetic variability in these eleven populations with the proportion of polymorphic loci ( P ) ranging from 6 25% to 12 50% (mean 6 82%), average number of alleles per locus (A) from 1 06 to 1 13(mean 1 07), average expected heterozygosity ( He) per locus from 0 032 to 0 054 (mean 0 035), and average observed heterozygosity Ho =0 063. The genotypes of locus Pgm-1 were heterozygous, and the other loci were homozygous. There existed low degree of population differentiation among the populations with G ST value as low as 0 030, which was very different from the published results of other tropical forests species. The homogeneity of genetic structure of Parashorea chinensis could be the impacts from several factors including the inbreeding (apomixis, selfing) in populations, and the bottleneck effect occurring in its evolution, which led to the much loss of genetic variability.