猕猴桃属植物的cpSSR遗传多样性及其同域分布物种的杂交渐渗与同塑

Genetic diversity,gene introgression and homoplasy in sympatric populations of the genus Actinidia as revealed by chloroplast microsatellite markers

同域分布的近缘物种常常发生杂交而导致种间基因渐渗,从而对相关物种的自然居群遗传结构产生重要影响,近缘种间的杂交渐渗已成为进化生物学和保护生物学关注的热点。本研究采用8对cpSSR引物对我国西部高原台地向中东部丘陵平原过渡地带同域重叠分布的猕猴桃属(Actinidia)7个物种的自然居群遗传多样性、居群遗传结构和同域分布种间遗传分化进行了检测。结果表明:(1)在6个多态性位点检测到18个等位基因形成的42个单倍型,尽管各单倍型间显示了复杂的网状进化关系,但还是具有明显的物种特异性;(2)各物种有丰富的cpSSR遗传多样性,但种间存在较大差异,绵毛猕猴桃(Actinidia fulvicoma var.lanata)的遗传多样性水平最高(P=62.50%,hT=0.173,HT=0.897),美味猕猴桃(A.deliciosa)的最低(P=37.5%,hT=0.041,HT=0.516);(3)尽管不同物种的居群分化程度存在较大差异,但种内居群间存在明显分化(GST为0.319-0.780,FST为0.401-0.695),居群间的基因流不足(Nm为0.219-0.747<1);其中以美味猕猴桃的居群遗传分化度最高(GST=0.780,FST=0.695);(4)遗传分化系数GST(unordered alleles)与NST(ordered alleles)无显著差异,揭示本研究的大多数猕猴桃属物种不存在系统地理结构,与用Mantel检验得出的居群遗传距离和地理距离不存在显著性相关的结果一致;(5)除了中华/美味猕猴桃复合体(A.chinensis/A.deliciosa complex)的湖北五峰(HW)和广西资源(GZ)两个同域复合居群外,同域分布的物种间遗传分化强烈(FST为0.476-0.990),与UPGMA聚类时多数居群按各自物种聚类的结果一致。进一步分析表明,中华/美味猕猴桃复合体近缘种间存在明显的共祖多态性和杂交渐渗现象,近缘种植株分布的交错程度以及是否存在亚居群结构对杂交渐渗存在着重要影响。亲缘关系较远的物种间杂交渐渗事件稀少,但存在个别同塑事件。本研究结果有助于进一步了解猕猴桃属植物自然居群cpDNA的遗传特性和渐渗杂交进化模式,为我国猕猴桃野生种质资源保育及可持续开发利用提供基础数据和科学依据。

Gone introgression usually results from spontaneous hybridization occurring among closely related species in sympatric populations and thus has great impact on the genetic structure of natural populations. This phenomenon has recently become one of the most active subjects in study of evolutionary and conservation biology. In the present study, eight chloroplast microsatellite （cpSSR） primers were used to examine genetic diversity, population genetic structure and hybridization introgression among seven Actinidia species with overlapping distributions in transitional regions ranging from the western China plateau to the middle-eastern China hilly mountains. The results showed： （1） A total of 42 haplotypes designated by 18 alleles at six polymorphic loci were detected across 655 individuals of the ten sympatric populations sampied. Although a reticulate evolutionary relationship was revealed among cpSSR haplotypes, there existed a strong species-specific tendency. （2） The intra-specific genetic diversity was generally high but varied greatly among different species. A. fulvicoma var. lanata showed the highest genetic diversity （P = 62.50%, hT = 0.173, HT= 0.897） whereas A. deliciosa exhibited the lowest （P = 37.5%, hT= 0.041, HT= 0.516）. （3） High level of inter-population genetic differentiation （GST and FST varied from 0.319 to 0.780 and 0.40 to 0.695, respectively） and limited gene flow （Nm ranged from 0.219 to 0.747〈1） were detected among the different species, of which A. deliciosa showed the highest inter-population genetic differentiation （GST = 0.780, FST= 695）. （4） No significant difference was found between Gst （unordered alleles） and Nst （ordered alleles）, suggesting a lack of phylogeographical structure for most Actinidia species. This is consistent with the Mantel test which revealed no significant relationship between genetic distance and geographical distance. （5） Interestingly, a relatively high level of inter-specific genetic differentiation was detected among species in sympatric populations （FST ranged from 0.476 to 0.990）, except for two populations （HW and GZ） of the A. chinensis/A. deliciosa complex. The result was also well in accordance with UPGMA analysis, which revealed that the populations tended to cluster together into the same species. Further analysis indicated that the A. chinensis/A. deliciosa complex was probably highly influenced by both shared ancestral chloroplast polymorphism and recent hybridization introgression. However, hybridization introgression rarely occurred between less related species, suggesting homoplasy events may have also played an important role in shaping phylogenetic relationships in the genus. The results have important implications for understanding population genetics and evolutionary patterns in the genus Actinidia and provide baseline data for formulating conservation and management strategies.