Bacilieri Roberto, Ducousso Alexis, Petit Rémy J, Kremer Antoine
Laboratoire de génétique et d'amélioration des arbres forestiers, Institut National de la Recherche Agronomique, B.P. 45, 33611, Gazinet, Cestas, France.
Evolution. 1996 Apr;50(2):900-908. doi: 10.1111/j.1558-5646.1996.tb03898.x.
The sessile (Quercus petraea [Matt.] Liebl.) and pedunculate (Quercus robur L.) oaks are two closely related species having a wide sympatric distribution over Europe. Under natural conditions, they frequently form mixed forests, where hybridization is suspected to occur. In this paper, two different approaches have been applied to the study of the mating system and the interspecific gene flow in a mixed stand formed by the two species. The mating systems of both species have been studied separately by means of the mixed-mating model. The relative contribution of the parental species to the progenies have been estimated with two different methods. The first uses the admixture model. The second is an extension of the mixed-mating model and subdivides the outcrossing rate into intra- and interspecific components. The two species were almost completely outcrossing. This high level of outcrossing and interspecific gene flow could play an important role in the maintenance of the genetic diversity in these long-lived forest tree species. The contribution of the sessile oak to the pedunculate oak progenies varied from 17% to 48%. In contrast, ovules of sessile oak trees appear to be preferentially fertilized by other extreme sessile genotypes. We suggest that interspecific and directional gene flow was responsible for such patterns. Pedunculate oak is considered as a pioneer species and is progressively replaced by sessile oak. Our present findings add a further genetic component to this succession scheme, suggesting that unidirectional gene flow reinforces succession between the two species.
无柄栎（Quercus petraea [Matt.] Liebl.）和有柄栎（Quercus robur L.）是两个亲缘关系密切的物种，在欧洲广泛分布且同域共存。在自然条件下，它们常常形成混交林，人们怀疑在其中会发生杂交现象。本文运用了两种不同方法来研究由这两个物种构成的混交林中的交配系统和种间基因流。通过混合交配模型分别研究了两个物种的交配系统。用两种不同方法估算了亲本物种对后代的相对贡献。第一种方法使用混合模型。第二种方法是混合交配模型的扩展，将异交率细分为种内和种间组分。这两个物种几乎完全异交。这种高水平的异交和种间基因流可能在维持这些长寿林木物种的遗传多样性方面发挥重要作用。无柄栎对有柄栎后代的贡献在17%至48%之间变化。相比之下，无柄栎树的胚珠似乎优先被其他极端的无柄栎基因型受精。我们认为种间和定向基因流是造成这种模式的原因。有柄栎被视为先锋物种，并逐渐被无柄栎取代。我们目前的研究结果为这一演替过程增添了另一个遗传因素，表明单向基因流强化了两个物种之间的演替。
