三峡库区特有种疏花水柏枝的保护遗传学研究

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对三峡库区特有种疏花水柏枝 (Myricarialaxiflora)的 13个自然居群和 1个人工迁地保护居群的等位酶遗传变异进行了初步研究。检测了 5个酶系统 ,得到 13个等位酶位点 ,遗传多样性及其遗传结构分析结果表明 :疏花水柏枝具有较高水平的遗传多样性 ,平均多态位点比率P =78.7% ,每位点平均等位基因数A =1.8,平均预期杂合度He=0 .317,高于中国植物特有种的平均水平 ,且群体中杂合基因型个体偏多 ;其遗传变异主要发生于居群内 ( 84.86 % ) ,居群间又存在一定的遗传分化 (Gst=0 .15 14) ,居群间平均基因流Nm =1.40 1,居群间遗传距离为 0 .0 0 2～ 0 .176 ;UPGMA聚类分析显示疏花水柏枝在三峡湖北境内的白水河—泄滩一带分为上游和下游 2个居群组 ;武汉植物园迁地保护的混合居群基本保育了其遗传多样性总水平。在分析讨论疏花水柏枝遗传多样性与其繁育系统、生境及其起源进化的关系的基础上 ,探讨了疏花水柏枝濒危的主要原因 ,推断其应为第四纪冰期影响后的古孑遗种。最后 ,在评价迁地保护成果的基础上 ,提出了今后进一步保育的策略。

Conservation genetics of the endemic species Myricaria laxiflora (Tamaricaceae) in the Three-Gorges Reservoir area, Hubei

Allozymic variation of 13 natural populations and one ex situ population of Myricaria laxiflora were analyzed using isoelectric focusing in thin-layer polyacrylamide slab gels. Thirteen loci of five enzyme systems were examined and used for the analysis of population genetic diversity and structure. A high genetic diversity was observed in this species, with mean number of alleles per locus of A=1.8, mean percentage of polymorphic loci P=78.7% and average expected heterozygosity H e=0.317, which were higher than the average value of Chinese endemic plant species. An excess of heterozygous genotypes was found both in natural and ex situ populations, suggesting a slight deviation from the Hardy-Weinberg equilibrium in the populations. The total genetic diversity (H t) is 0.3733 within the species, while the genetic diversity within and among populations (H s vs Dst) were 0.3168 and 0.0565, respectively, indicating that 84.86% of the genetic variation occured within populations and only 15.14% among natural populations. The mean gene flow among populations (Nm) was 1.401 and genetic distances among populations ranges from 0.002 to 0.176. Cluster analysis using UPGMA on Rogers' genetic distance revealed that populations of M. laxiflora growing along riversides in the Three-Gorges Reservior area were separated into upstream and downstream groups at Baishui River, Xietan region in Hubei Province. A level of genetic diversity similar to that of natural populations was observed in the ex situ population at Wuhan Botanical Garden, so the ex situ conservation program was considered to be successful in preserving genetic diversity. Combining analysis of the genetic diversity with available information on breeding system, status of natural habitat, and evolutionary history, the causes for the endangerment of M. laxiflora are discussed. It is likely that the species gradually evolved as a relict species after the Quaternary Glaciation. Based on evaluation of the current ex situ conservation program, we suggest that similar habitats upstream and downstream of the Three-Gorges Reservoir or on nearby tributaries should be selected as ex situ conservation spots for M. laxiflora populations with high genetic diversity before their original habitats are submerged by the Three-Gorges Reservoir.