极濒危植物中华水韭休宁居群的遗传结构

Genetic structure of Xiuning population of Isoetes sinensis, a critically endangered species in China

采用超薄平板微型聚丙烯酰胺等电聚焦电泳方法对极濒危蕨类植物中华水韭 (Isoetessinensis)现存于安徽休宁的 5个亚居群的等位酶多样性和遗传结构进行了研究。结果表明 :中华水韭居群每位点平均等位基因数A =1.7,平均多态位点比率P =5 5 .5 6 % ,平均预期杂合度He=0 .2 0 1。居群中半数的多态位点表现为等位基因的“固定杂合” ,5个亚居群的遗传多样性无显著差异 ,但都表现出严重偏离Hardy Weinberg平衡的杂合子过量 ;其遗传变异主要发生于亚居群内 (94 .2 7% ) ,亚居群之间的遗传分化较小 (Gst=0 .0 5 73) ,亚居群间遗传一致度较高 (I =0 .96 0 - 0 .999)。我们推断这可能是由于居群构建之初的奠基者效应或者原种群曾经历了较为严重的遗传瓶颈所导致 ;此外亚居群间便利的基因交流也可能起到了很大作用 (Nm =4 .5 0 6 2 )。取自休宁居群的 75株样品由 13个专一多位点基因型 (18个位点等位酶基因型 )组成 ,亚居群及个体间高度遗传均质。本文还就中华水韭休宁野生居群濒危的遗传因素进行了探讨 ,并提出了相应的保育策略。

Allozymic variation and genetic structure of five subpopulations of Isoetes sinensis sampled from Xiuning, Anhui Province were investigated using isoelectric focusing in thin-layer polyacrylamid slab gels. Eighteen loci of 10 enzyme systems were examined and used for the analysis of population genetic parameters. A high genetic diversity was observed in the population, with mean number of alleles per loci (A)=1.7, mean percentage of polymorphic loci(P)=55.56 %, and average expected heterozygosity (H e) =0.201. These parameters of genetic diversity were much higher than the average values in fern species. Excess fixed heterozygotes “aabb” found in the population were greatly responsible for deviation from Hardy-Weinberg equilibrium at some polymorphic loci. No significant difference in genetic variation was found among the five subpopulations. Partitioning the genetic diversity indicated that 94.27% of the genetic variation was within subpopulations and only 5.73% existed between subpopulations, which was explained by a genetic bottleneck or founder effect, as well as by the clonal reproduction of this species and “fixed heterozygosity”. Mean gene flow among subpopulations (Nm) was 4.5062 and genetic identities among subpopulations ranged from 0.960 to 0.999, which is suggestive evidence that the Xiuning population is panmictic in its current habitat. Furthermore, the sampled population with a total of 75 individuals consists of only 13 multi-locus genotypes, suggesting a high genetic uniformity within and among subpopulations. Finally, we discuss the risk of extinction of this species in the wild driven by population genetic factors, and conservation strategies.