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

生物多样性 2007, 15 (1): 1-22 doi: 10.1360/biodiv.060277 Biodiversity Science http: //

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

张田1, 2**李作洲1**刘亚令1, 3姜正旺1黄宏文1*

1 (中国科学院武汉植物园, 武汉 430074)

2 (中国科学院研究生院, 北京 100049)

3(华中农业大学园艺林学学院, 武汉 430074)

摘要: 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%, h T =

0.173, H T = 0.897), 美味猕猴桃(A.deliciosa)的最低(P = 37.5％, h T = 0.041, H T = 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(G ST为0.319–0.780, F ST为0.401–0.695), 居群间的基因流不足(N m为0.219–0.747<1); 其中以美味猕猴桃的居群遗传分化度最高(G ST = 0.780, F ST = 0.695); (4)遗传分化系数

G ST(unordered alleles)与N ST(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(F ST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。

关键词: 猕猴桃, 叶绿体SSR, 基因渐渗, 遗传多样性, 遗传结构, 共祖多态性, 同塑效应

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

Tian Zhang 1, 2**, Zuozhou Li 1**, Yaling Liu 1, 3, Zhengwang Jiang 1, Hongwen Huang 1*

1 Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074

2 Graduate School of the Chinese Academy of Sciences, Beijing 100049

3 College of Horticulture and Forestry, Huazhong Agricultural University, Wuhan 430074

Abstract: Gene introgression usually results from spontaneous hybridization occurring among closely re-lated species in sympatric populations and thus has great impact on the genetic structure of natural popula-tions. This phenomenon has recently become one of the most active subjects in study of evolutionary and

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收稿日期: 2006-11-16; 接受日期: 2006-12-11

基金项目: 中国科学院武汉植物园创新主任基金(05035117)和中国科学院知识创新方向性项目(KSCX2-SW-320; KSCX2-SW-104)

*通讯作者Author for correspondence. E-mail: hongwen@

**同等贡献作者The two authors contributed equally to this work.

2 生物多样性 Biodiversity Science第15卷

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 Acti-nidia 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 sam-pled. 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%, h T =

0.173, H T = 0.897) whereas A.deliciosa exhibited the lowest (P = 37.5％, h T = 0.041, H T = 0.516). (3) High

level of inter-population genetic differentiation (G ST and F ST varied from 0.319 to 0.780 and 0.40 to 0.695, respectively) and limited gene flow (N m 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 (G ST = 0.780, F ST = 695). (4) No significant difference was found between G st (unordered alleles) and N st (ordered alleles), sug-gesting 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) Inter-estingly, a relatively high level of inter-specific genetic differentiation was detected among species in sym-patric populations (F ST 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 re-vealed 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 conserva-tion and management strategies.

Key words:Actinidia, cpSSR, introgression, genetic diversity, genetic differentiation, ancestral polymor-phism, homoplasy

生物的自然种间杂交和反复回交使一个物种的遗传物质穿越种间障碍转入到另一个物种内, 形成基因渐渗(gene introgression)(Anderson, 1953), 导致种间基因流动。自然杂交和种间基因渐渗是植物界的普遍现象, 是促进遗传变异的一个重要途径, 在物种进化历程中扮演着重要角色(Tovar-Sanchez & Oyama, 2004; van Droogenbroeck et al., 2006)。一方面物种间的杂交渐渗可产生新的基因型组合和生态型, 提高物种的遗传多样性, 使其更好地适应不断改变的生态环境或增加新的生境适应性, 有利于促进物种散布和种群扩张; 同时杂交还可以打破或降低繁殖壁垒, 形成多样化的杂种, 而杂种后代可能在微生境的差异、生态因素的区别性选择、资源的竞争和不同的取舍方式等因素的驱动下, 导致物种的趋异而产生新的物种类群(Rieseberg et al., 2003; Barluenga et al., 2006)。

另一方面, 在人类活动干扰或自然环境变化过程中, 种间基因流和杂交可能导致原生境隔离的近缘物种间产生杂交没化(hybridization merging), 使得物种间的区别不再像以前明显进而导致物种合并(Rieseberg & Carney, 1998; Gross et al., 2004), 形成不同分类群间遗传同化(genetic assimilation)现象; 同时, 种间杂交可能与种内交配形成竞争, 减少种内繁育后代的几率, 杂种F1代所具有的营养生长杂种优势一方面可能使种内后代在争夺生态位或领地方面处于劣势, 另一方面杂交也可能直接导致某些植物类群的杂合子劣势而产生远交衰退(outbreeding depression)(Becker et al., 2006)。此外, 当本地物种竞争能力弱、数量少、生殖壁垒不强时, 外来物种与本地种的杂交会威胁到本地物种基因组的完整性和原始性, 在很短世代内, 可能直接或间接地导致物种濒危甚至灭绝(Huxel, 1999; Wolf et al., 2001)。

尽管近一个世纪以来人们对杂交和杂交带在