Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Kasteelpark Arenberg 31, Heverlee, B-3001, Belgium.
BMC Evol Biol. 2012 Sep 12;12:178. doi: 10.1186/1471-2148-12-178.
In food-deceptive orchids of the genera Anacamptis, Neotinea and Orchis floral isolation has been shown to be weak, whereas late-acting reproductive barriers are mostly strong, often restricting hybridization to the F1 generation. Only in a few species hybridization extends beyond the F1 generation, giving rise to hybrid swarms. However, little is known about the abundance of later-generation hybrids and what factors drive their occurrence in hybrid populations. In this study, molecular analyses were combined with detailed morphological measurements in a hybrid population of two closely related Orchis species (Orchis militaris and O. purpurea) to investigate the hypothesis that the abundance of later-generation hybrids is driven by changes in floral characters after hybridization that exert selective pressures that in turn affect hybridization.
Both the molecular and morphological data point to extensive genetic and morphological homogenization and asymmetric introgression. Estimating genomic clines from the multi-locus genotype data and testing for deviation from neutrality revealed that 30 out of 113 (27%) AFLP markers significantly deviated from neutral expectations. Plants with large floral displays or plant with flowers that resembled more O. purpurea had higher female fitness than plants with small floral displays or plants with flowers resembling more O. militaris, suggesting that directional selection may have contributed to the observed patterns of introgression.
These results indicate that in closely related orchid species hybridization and gene introgression may be partly driven by selection for floral traits of one of the parental types. However, because some pure individuals were still present in the studied population, the parental species appeared to be sufficiently isolated to survive the challenge of sympatry.
在欺骗性兰花属（Anacamptis、Neotinea 和 Orchis）中，花的隔离较弱，而晚期生殖障碍较强，常常限制杂交仅限于 F1 代。只有在少数物种中，杂交扩展到 F1 代之外，产生杂种群。然而，对于后期杂种的丰度以及哪些因素驱动它们在杂种群体中发生的了解甚少。在这项研究中，分子分析与两种密切相关的兰花物种（Orchis militaris 和 O. purpurea）杂种群的详细形态测量相结合，以检验以下假设：后期杂种的丰度是由杂交后花部特征的变化驱动的，这些变化施加了选择性压力，进而影响了杂交。
分子和形态数据都指向广泛的遗传和形态同质化以及不对称的基因渗入。从多基因座基因型数据估计基因组梯度，并检测是否偏离中性，发现 113 个 AFLP 标记中有 30 个（27%）显著偏离中性预期。具有大花展示或花朵更像 O. purpurea 的植物比具有小花展示或花朵更像 O. militaris 的植物具有更高的雌性适合度，表明定向选择可能导致了观察到的基因渗入模式。
这些结果表明，在密切相关的兰花物种中，杂交和基因渗入可能部分是由对亲本类型之一的花部特征的选择驱动的。然而，由于研究种群中仍存在一些纯合个体，亲本物种似乎足够隔离以应对同域挑战。
