González-Rodríguez Antonio, Arias Dulce M, Valencia Susana, Oyama Ken
Centro de Investigaciones en Ecosistemas, Universidad Nacional Autónoma de México, Antigua Carretera a Pátzcuaro No. 8701, Col. Ex-Hacienda de San José de la Huerta, Morelia, 58190 Michoacán, México;
Am J Bot. 2004 Mar;91(3):401-9. doi: 10.3732/ajb.91.3.401.
Quercus affinis and Q. laurina are two closely related Mexican red oaks with partially overlapping distributions. Within the area of overlap, there are localities where morphological intergradation occurs. A previous hypothesis explained this pattern as a result of secondary contact between the two species, followed by hybridization and introgression. This possibility was analyzed here by examining foliar and genetic variation in 16 localities situated along a macrogeographic gradient, which included morphologically representative populations of both species and populations from within the area of overlap. Maximum-likelihood hybrid index scores calculated from nine semi-diagnostic RAPD markers indicated a shift in the genetic composition of populations from one species to the other along the macrogeographic gradient, with genetically intermediate populations situated in the area of overlap. Foliar variation followed a partially congruent pattern, but Q. laurina-like morphology predominated in some of the genetically intermediate populations. There were several instances of correlated frequency changeovers of single RAPD markers and morphological characters along the macrogeographic gradient and a few cases of markedly parallel patterns between markers. The results were interpreted as consistent with a hypothesis of secondary contact between the two oak species that has resulted in some differential introgression among markers.
墨西哥柔毛栎（Quercus affinis）和劳氏栎（Q. laurina）是两种亲缘关系密切的墨西哥红栎，分布范围部分重叠。在重叠区域内，存在形态渐变的地点。先前的一个假说是，这种模式是由于这两个物种之间的二次接触，随后发生杂交和基因渐渗导致的。在此，通过研究沿宏观地理梯度分布的16个地点的叶片和遗传变异来分析这种可能性，这些地点包括两个物种形态上具有代表性的种群以及重叠区域内的种群。根据9个半诊断性RAPD标记计算出的最大似然杂交指数得分表明，沿着宏观地理梯度，种群的遗传组成从一个物种向另一个物种发生了转变，基因中间型种群位于重叠区域。叶片变异呈现出部分一致的模式，但在一些基因中间型种群中，劳氏栎样形态占主导。沿着宏观地理梯度，有几个单RAPD标记和形态特征的频率变化相关的实例，并且标记之间有一些明显平行的模式。结果被解释为与这两种栎树之间二次接触的假说一致，这种接触导致了标记之间一些不同程度的基因渐渗。
