两个二倍体杜鹃物种之间的杂交群中，不对称自然杂交情况各不相同。
Asymmetrical natural hybridization varies among hybrid swarms between two diploid Rhododendron species.
作者信息
Yan Li-Jun, Burgess Kevin S, Milne Richard, Fu Chao-Nan, Li De-Zhu, Gao Lian-Ming
机构信息
Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China.
Germplasm Bank of Wild Species in Southwest China, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China.
出版信息
Ann Bot. 2017 Jul 1;120(1):51-61. doi: 10.1093/aob/mcx039.
BACKGROUND AND AIMS
The extent to which hybridization leads to gene flow between plant species depends on the structure of hybrid populations. However, if this varies between locations, species barriers might prove permeable in some locations but not in others. To assess possible variation in hybrid population structure, the magnitude and direction of natural hybridization between two Chinese endemic species, Rhododendron spiciferum and Rhododendron spinuliferum , were evaluated.
METHODS
Thirteen nuclear microsatellite markers were employed to characterize 566 individuals collected from 15 non-allopatric populations and nine allopatric parental populations. Chloroplast DNA (cpDNA) sequences were obtained from a subset of samples. Genetic structure and direction of gene flow was determined using a combination of STRUCTURE and NEWHYBRIDS analysis.
KEY RESULTS
Nuclear analysis revealed that parental taxa formed two genetically distinct clusters and hybrids shared the genetic background of both parents and did not form a separate genetic lineage. Overall, hybrid swarms were dominated by early- and later-generation hybrids, with a significantly higher proportion of hybrids (59·6 %) possessing >50 % R. spiciferum-like nuclear germplasm. The cpDNA analysis further indicated that a significantly greater proportion of hybrids (61·1 %) possessed the R. spiciferum cpDNA haplotype.
CONCLUSIONS
Gene flow between R. spiciferum and R. spinuliferum was found to be bidirectional in 14 of the 15 hybrid swarms and asymmetrical in six hybrid swarms. Asymmetrical gene flow was evident for only nuclear DNA (nDNA) in two populations, for only cpDNA in three populations, and for both nDNA and cpDNA in one population. Collectively, the variation in genetic structure found among the 15 hybrid swarms suggests that introgression rather than hybrid speciation is a more likely outcome of hybridization between these hybridizing taxa.
背景与目的
杂交导致植物物种间基因流动的程度取决于杂交种群的结构。然而，如果这种情况在不同地点有所变化，物种屏障可能在某些地点是可渗透的，而在其他地点则不然。为了评估杂交种群结构的可能变化，对中国特有物种刺毛杜鹃（Rhododendron spiciferum）和毛棉杜鹃（Rhododendron spinuliferum）之间自然杂交的程度和方向进行了评估。
方法
使用13个核微卫星标记对从15个非异域种群和9个异域亲本种群收集的566个个体进行特征分析。从一部分样本中获得叶绿体DNA（cpDNA）序列。使用STRUCTURE和NEWHYBRIDS分析相结合的方法确定基因结构和基因流动方向。
主要结果
核分析表明，亲本类群形成了两个遗传上不同的簇，杂种具有双亲的遗传背景，没有形成单独的遗传谱系。总体而言，杂交群体以早期和晚期杂种为主，具有>50%刺毛杜鹃样核种质的杂种比例显著更高（59.6%）。cpDNA分析进一步表明，具有刺毛杜鹃cpDNA单倍型的杂种比例显著更高（61.1%）。
结论
在15个杂交群体中的14个中，发现刺毛杜鹃和毛棉杜鹃之间的基因流动是双向的，在6个杂交群体中是不对称的。在两个种群中，仅核DNA（nDNA）存在不对称基因流动；在三个种群中，仅cpDNA存在不对称基因流动；在一个种群中，nDNA和cpDNA均存在不对称基因流动。总体而言，在15个杂交群体中发现的遗传结构变化表明，渗入而非杂交物种形成是这些杂交类群之间杂交更可能产生的结果。
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