dePamphilis Claude W, Wyatt Robert
Department of Botany, University of Georgia, Athens, GA, 30602, USA.
Evolution. 1990 Aug;44(5):1295-1317. doi: 10.1111/j.1558-5646.1990.tb05233.x.
Within a broad (>200 km wide) hybrid zone involving three parapatric species of Aesculus, we observed coincident clines in allele frequency for 6 of 14 electrophoretic loci. The cooccurrence of alleles characteristic of A. pavia, A. sylvatica, and A. flava was used to estimate genetic admixtures in 48 populations involving various hybrids between these taxa in the southeastern United States. High levels of allelic polymorphism (up to 40% greater than the parental taxa) were observed in hybrid populations and also in some populations bordering the hybrid zone. A detailed analysis of a portion of the hybrid zone involving A. pavia and A. sylvatica revealed a highly asymmetrical pattern of gene flow, predominantly from Coastal Plain populations of A. pavia into Piedmont populations of A. sylvatica. Computer simulations were used to generate expected genotypic arrays for parental, F ; and backcross individuals, which were compared with natural populations using a character index scoring system. In these comparisons, hybrid individuals could be distinguished from either parent, but F and backcross progeny could not be distinguished from each other. Most hybrid populations were found to include hybrids and one of the parental taxa, but never both parents. Three populations appeared to be predominantly hybrids with no identifiable parental individuals. Hybrids occurred commonly at least 150 km beyond the range of A. pavia, but usually not more than 25 km beyond the range of A. sylvatica. Introgression, suggested by genetically hybrid individuals and significant gene admixtures of two or more species in populations lacking morphological evidence of hybridization, may extend the hybrid zone further in both directions. The absence of one or both parental species from hybrid populations implies a selective disadvantage to parentals in the hybrid zone and/or that hybridization has occurred through long-distance gene flow via pollen, primarily from A. pavia into A. sylvatica. Long-distance pollen movement in plants may generate hybrid zones of qualitatively different structure than those observed in animals, where gene flow involves dispersal of individuals.
在一个广泛的（宽度超过200千米）涉及七叶树属三个邻域物种的杂交带内，我们观察到14个电泳位点中的6个位点的等位基因频率存在一致的渐变群。利用红花七叶树、美洲七叶树和黄花七叶树特有的等位基因的同时出现，来估计美国东南部这几个分类群之间各种杂种的48个种群中的遗传混合情况。在杂种种群以及杂交带边缘的一些种群中，观察到了高水平的等位基因多态性（比亲本分类群高40%）。对涉及红花七叶树和美洲七叶树的部分杂交带进行的详细分析揭示了一种高度不对称的基因流动模式，主要是从红花七叶树的沿海平原种群流向美洲七叶树的皮埃蒙特种群。计算机模拟被用来生成亲本、F1和回交个体的预期基因型阵列，并使用性状指数评分系统将其与自然种群进行比较。在这些比较中，杂种个体可以与任何一个亲本区分开来，但F1和回交后代彼此无法区分。大多数杂种种群被发现包含杂种和一个亲本分类群，但从未同时包含两个亲本。有三个种群似乎主要是杂种，没有可识别的亲本个体。杂种通常出现在红花七叶树分布范围之外至少150千米处，但通常不会超出美洲七叶树分布范围25千米以上。缺乏杂交形态学证据的种群中存在遗传杂种个体以及两个或更多物种的显著基因混合，这表明渐渗可能会使杂交带在两个方向上进一步扩展。杂种种群中缺少一个或两个亲本物种，这意味着亲本在杂交带中存在选择劣势，和/或杂交是通过花粉的长距离基因流动发生的，主要是从红花七叶树流向美洲七叶树。植物中的长距离花粉移动可能会产生结构与动物中观察到的不同的杂交带，动物中的基因流动涉及个体的扩散。
