Data from: Asymmetric introgression between Magnolia stellata and M. salicifolia at a site where the two species grow sympatrically

In order to understand the ongoing evolutionary relationships between species, it is important to elucidate patterns of natural hybridization. In the zone where two species are sympatrically distributed, we examined 274 individuals of Magnolia stellata, Magnolia salicifolia, and their putative hybrids by means of 16 nuclear and three chloroplast microsatellite markers. Hybrid classes of individuals were estimated by admixture analyses. Morphological traits were also investigated for 64 of the 274 individuals. Admixture analyses revealed that 66 of the 274 individuals were classified as hybrids, comprising 17 F1 and 19 F2 individuals, 27 backcrosses to M. salicifolia, and 3 individuals of unknown origin. Morphological data from the 64 individuals agreed well with their genetic admixture rates. Spatial locations of F1 and F2 hybrids at the study site were intermediate between the two purebred species, indicating that the site preferences of hybrids are intermediate. The occurrences of F2 and backcross hybrids indicate that F1 hybrids are fertile. The chloroplast DNA haplotypes of all F1 hybrids corresponded to those detected in M. salicifolia, so that maternal parents of the F1 hybrids were all M. salicifolia. Furthermore, no hybrid individuals derived from a backcross to M. stellata were detected. These results suggest that the direction of hybridization and the subsequent introgression have been quite asymmetric and that the introgression occurred from M. stellata into M. salicifolia.

为阐明物种间持续的演化关系，解析自然杂交模式具有重要意义。在两种木兰属物种同域分布的研究区域内，我们利用16个核微卫星标记（nuclear microsatellite markers）和3个叶绿体微卫星标记（chloroplast microsatellite markers），对274个星花木兰（Magnolia stellata）、柳叶木兰（Magnolia salicifolia）及其推定杂种个体进行了分析。我们通过遗传混合分析（admixture analyses）对个体的杂交类别进行了推断，并对274个个体中的64个开展了形态性状调查。遗传混合分析结果显示，274个个体中有66个被归类为杂种，其中包括17个子一代（F₁）、19个子二代（F₂）个体、27个与柳叶木兰的回交个体，以及3个起源未知的个体。64个个体的形态学数据与其遗传混合比例高度吻合。研究区域内F₁和F₂杂种的空间分布位置介于两个纯种物种之间，表明杂种的生境偏好同样处于二者的中间状态。F₂和回交杂种的存在证实F₁杂种具有可育性。所有F₁杂种的叶绿体DNA单倍型均与柳叶木兰中检测到的单倍型一致，由此可知F₁杂种的母本均为柳叶木兰。此外，未检测到与星花木兰回交所产生的杂种个体。上述结果表明，杂交方向及后续的基因渐渗（introgression）过程具有显著的不对称性，且基因渐渗是从星花木兰向柳叶木兰进行的。