内蒙古中东部不同草原地带羊草种群遗传分化

Genetic differentiation within and between Leymus chinensis populations from different zones of Mid-Eastern Inner Mongolia steppe

运用 RAPD技术对内蒙古不同草原地带分布的 5个羊草种群 (共 10 0个个体 )的遗传多样性进行分析。 31个随机引物(10 nt)在 5个羊草种群中共检测到 4 96个扩增片断 ,其中多态性片断 4 89个 ,总的多态位点百分率达 98.6 %。利用 Nei指数和Shannon指数估算了 5个种群的遗传多样性 ,并计算种群相似系数和遗传距离运用 UPGMA法进行聚类分析。结果表明 :无论是种群内还是种群间 ,羊草均存在较高的遗传变异 ,大部分的遗传变异存在于种群内 (Nei指数和 Shannon指数估算结果分别为 85 .4 %和 72 .5 % ) ,只有少部分的遗传变异存在于种群间 ;不同种群的遗传多样性存在差异 ,各种群的遗传多样性与其所处的地理位置具有显著的相关性 ;5个种群的平均遗传距离为 0 .5 0 95 ,变异范围为 0 .4 6 84～ 0 .5 4 76 ;聚类分析结果显示地理距离较近的种群遗传距离较小 ,首先聚在一起 ,而地理距离较远的种群遗传距离较大 ,说明羊草种群间的遗传分化与地理距离存在一定相关性 ;但地理距离最近的两个种群并未最先聚集 。

Randomly amplified polymorphic DNA(RAPD) analysis was applied to five populations(100 individuals altogether)of Leymus chinensis from different steppe zones of Inner Mongolia. The number of DNA bands amplified per primer was 15.7 on average. The number of DNA bands amplified per plant among the five populations decreased with the increase of longitude, and there existed a negative correlation between the number of bands per plant and the longitude. A total of 496 amplified fragments were detected using 31 random primers, among which 489 loci (98.6%) were polymorphic. The genetic diversity of Leymus chinensis was relatively high and the genetic variation existed mainly within the populations (Nei Index and Shannon Index were 85.4% and 72.5% respectively). High intraspecific genetic diversity of Leymus chinensis was the genetic basis for its adaptive ability to various environments, its wide distribution and high tolerance. The genetic diversity level among the five populations varied with their geographic locations that differed in environmental factors such as humidity and temperature. Natural selection pressure might have had an effect on the level of genetic diversity. In terms of proportion of polymorphic loci and genetic diversity of the populations, Keshiketeng population had the highest genetic diversity, followed by Abaga population, and Huolinguole population had the lowest genetic diversity. A strong flow occurred among the populations, with the number of migrants per generation (Nm) being 1.622, which might have prevented Leymus chinensis populations from differentiation due to genetic drift. Similarity and genetic distance matrices were established from the RAPD data on the basis of Nei's estimation methods, and dendrograms were constructed based on UPGMA clustering. The average genetic distance among the five populations was 0.5095, varying from 0.4684 to 0.5476, which indicated that there were relatively high genetic variations and differentiations among the five populations in the study area. There was a significantly positive correlation between genetic differentiation and geographic distance among Leymus chinensis populations. The populations from farther locations were clustered into a group lastly, while the populations with shortest geographic distance were not aggregated in the first group. These results implied that the level of genetic differentiation of Leymus chinensis was related in a large scale to environment gradient, but was affected in a smaller scale by more ecological factors of its habitat.