Moccia Maria Domenica, Widmer Alex, Cozzolino Salvatore
Dipartimento delle Scienze Biologiche, Università degli Studi di Napoli Federico II, Via Foria, 223, I-80139 Naples, Italy.
Mol Ecol. 2007 Jul;16(14):2855-66. doi: 10.1111/j.1365-294X.2007.03240.x.
Reproductive isolation is of fundamental importance for maintaining species boundaries in sympatry. In orchids, the wide variety of pollination systems and highly diverse floral traits have traditionally suggested a prominent role for pollinator isolation, and thus for prezygotic isolation, as an effective barrier to gene flow among species. Here, we examined the nature of reproductive isolation between Anacamptis morio and Anacamptis papilionacea, two sister species of Mediterranean food-deceptive orchids, in two natural hybrid zones. Comparative analyses of the two hybrid zones that are located on soils with volcanic origin and have different and well-dated ages consistently revealed that all hybrid individuals were morphologically and genetically intermediate between the parental species, but had strongly reduced fitness. Molecular analyses based on nuclear ITS1 and (amplified fragment length polymorphism) AFLP markers clearly showed that all examined hybrids were F1 hybrids, and that no introgression occurred between parental species. The maternally inherited plastid DNA markers indicated that hybridization between A. morio and A. papilionacea was bidirectional, as confirmed by the molecular analysis of seed families. The genetic architecture of the two hybrid zones suggests that the two parental species easily and frequently hybridize in sympatry as a consequence of partial pollinator overlap but that strong postzygotic barriers reduce hybrid fitness and prevent gene introgression. These results corroborate that chromosomal divergence is instrumental for reproductive isolation between these food-deceptive orchids and suggest that hybridization is of limited importance for their diversification.
生殖隔离对于在同域中维持物种界限至关重要。在兰花中，传统上认为多种多样的传粉系统和高度多样的花部特征表明传粉者隔离发挥着重要作用，因此对于合子前隔离而言，它是物种间基因流动的有效障碍。在此，我们在两个自然杂交区研究了地中海食源性欺骗型兰花的两个姊妹种——莫氏红门兰（Anacamptis morio）和蝶形红门兰（Anacamptis papilionacea）之间生殖隔离的本质。对位于火山源土壤上且年龄不同且有明确年代的两个杂交区进行的比较分析一致表明，所有杂交个体在形态和遗传上均介于亲本物种之间，但适应性大幅降低。基于核ITS1和（扩增片段长度多态性）AFLP标记的分子分析清楚地表明，所有检测到的杂种都是F1杂种，且亲本物种之间没有发生基因渐渗。母系遗传的质体DNA标记表明，莫氏红门兰和蝶形红门兰之间的杂交是双向的，种子家族的分子分析证实了这一点。两个杂交区的遗传结构表明，由于部分传粉者重叠，这两个亲本物种在同域中容易且频繁地杂交，但强大的合子后障碍降低了杂种适应性并阻止了基因渐渗。这些结果证实，染色体分歧有助于这些食源性欺骗型兰花之间的生殖隔离，并表明杂交对它们的多样化作用有限。
