中华猕猴桃和美味猕猴桃自然居群遗传结构及其种间杂交渐渗

 利用9对SSR引物对中华猕猴桃（Actinidia chinensis）和美味猕猴桃（A. deliciosa）两近缘种的5个同域分布复合体和各自1个非同域分布居群进行了遗传多样性、居群遗传结构的分析以及种间杂交渐渗的探讨。结果表明：1）两物种共有等位基因比例高达81.13%，物种特有等位基因较少（中华猕猴桃：13.27%，美味猕猴桃：5.61%），但共享等位基因表型频率在两近缘种间存在差异，而且与各同域复合体中两物种样本的交错程度或间距存在关联；2）两种猕猴桃均具有极高遗传多样性，美味猕猴桃的遗传多样性（H_o＝0 .749， PIC＝0.818）都略高于中华猕猴桃（H_o＝0.686，PIC＝0.799）；3）两猕 猴桃物种均具有较低的Nei’s居群遗传分化度，但AMOVA分析结果揭示种内异域居群间（F_ST=0.091 5）和同域复合体种间（F_ST=0.111 5）均存在一定程度的遗传分化；中华猕猴桃居群遗传分化（G_ST=0.086; F_ST=0.212 1）高于美味猕猴桃（G_ST= 0.080;F_ST=0.142 0）；4）同域分布复合体两物种间的遗传分化（G_ST=0.020）低于物种内异域居群间的遗传分化（中华猕猴桃：G_ST=0.086; 美味猕猴桃：G_ST=0.080），同域复合体物种间的基因流（N_m＝7.89 -29.75）远远高于 同种异域居群间（中华猕猴桃：N_m =2.663; 美味猕猴桃：N_m=2.880）； 5）居群UPGMA聚类揭示在同一地域的居群优先聚类，个体聚类结果显示多数个体聚在各自居群组内，但各地理居群并不按地理距离的远近聚类，这与Mantel相关性检测所揭示的居群间遗传距离与地理距离没有显著性相关的结果一致。进一步分析表明两种猕猴桃的遗传多样性和居群遗传结构不仅受其广域分布、远交、晚期分化等生活史特性的影响，同时还与猕猴桃的染色体基数高 (x=29)、倍性复杂和种间杂交等因素密切相关，其中两种猕猴桃的共享祖先多态性和同域分布种间杂交基因渗透对两猕猴桃的居群遗传结构产生了重要影响。

GENETIC STRUCTURE AND HYBRIDIZATION INTROGRESSION IN NATURAL POPULATIONS OF TWO CLOSELY RELATED ACTINIDIA SPECIES, A. CHINENSIS AND A. DELICIOSA

Aims Gene introgression usually results from spontaneous hybridization in sympatric populations and has great impact on population genetic structure. Actinidia chinensis and A. deliciosa are two closely related species with different morphologies and polyploidy levels. Our objective was to analyze their genetic diversity, population genetic structure and hybridization introgression to clarify their evolutionary history and provide baseline data for conservation and management strategies.  Methods We investigated five sympatric complex populations and two allopatric populations of A. chinensis and A. deliciosa using nine pairs of SSR primers and analyzed genetic diversity and differentiation indexes within and between species.  Important findings We detected 196 alleles at the nine polymorphic loci among 432 individuals sampled from the seven locations. The percentage of alleles shared in the two species was 81.13%, and the percentage of species-specific alleles for A. chinensis and A. deliciosa was 13.27% and 5.61%, respectively. Intra-specific genetic diversity in both species was high. Nei’s genetic differentiation among populations within or between species was low, indicating high gene flow among populations and between the two species. The UPGMA dendrogram clustered the sympatric complex populations. Individuals also were clustered into their own populations, whereas no correlation was found between population clustering and geographic distance. We discuss the combined impacts of wide-range distribution, outcrossing, late differentiation and other life history characteristics, as well as genome size of the genus, complex ploidy level and interspecific hybridization on the genetic variation and population structure of these two sympatric species. We concluded that the shared ancestral genetic polymorphisms and recent hybridization introgression between species in sympatric complex populations likely played a key role in formulating population structure of Actinidia species.