Cortis P, Vereecken N J, Schiestl F P, Barone Lumaga M R, Scrugli A, Cozzolino S
Dipartimento di Scienze Botaniche, Università degli Studi di Cagliari, I-09123 Cagliari, Italy.
Ann Bot. 2009 Aug;104(3):497-506. doi: 10.1093/aob/mcn219. Epub 2008 Nov 10.
In the sexually deceptive Ophrys genus, species isolation is generally considered ethological and occurs via different, specific pollinators, but there are cases in which Ophrys species can share a common pollinator and differ in pollen placement on the body of the insect. In that condition, species are expected to be reproductively isolated through a pre-mating mechanical barrier. Here, the relative contribution of pre- vs. post-mating barriers to gene flow among two Ophrys species that share a common pollinator and can occur in sympatry is studied.
A natural hybrid zone on Sardinia between O. iricolor and O. incubacea, sharing Andrena morio as pollinator, was investigated by analysing floral traits involved in pollinator attraction as odour extracts both for non-active and active compounds and for labellum morphology. The genetic architecture of the hybrid zone was also estimated with amplified fragment length polymorphism (AFLP) markers, and pollination fitness and seed set of both parental species and their hybrids in the sympatric zone were estimated by controlled crosses.
Although hybrids were intermediate between parental species in labellum morphology and non-active odour compounds, both parental species and hybrids produced a similar odour bouquet for active compounds. However, hybrids produced significantly lower fruit and seed set than parental species, and the genetic architecture of the hybrid zone suggests that they were mostly first-generation hybrids.
The two parental species hybridize in sympatry as a consequence of pollinator overlap and weak mechanical isolation, but post-zygotic barriers reduce hybrid frequency and fitness, and prevent extensive introgression. These results highlight a significant contribution of late post-mating barriers, such as chromosomal divergence, for maintaining reproductive isolation, in an orchid group for which pre-mating barriers are often considered predominant.
在性欺骗的眉兰属植物中，物种隔离通常被认为是行为学上的，通过不同的特定传粉者发生，但存在眉兰属物种共享共同传粉者且在昆虫身体上的花粉放置位置不同的情况。在这种情况下，预计物种会通过交配前的机械障碍实现生殖隔离。在此，研究了交配前与交配后障碍对共享共同传粉者且可同域分布的两种眉兰属物种间基因流动的相对贡献。
通过分析参与吸引传粉者的花部特征，如非活性和活性化合物的气味提取物以及唇瓣形态，对撒丁岛上鸢尾眉兰和孵化眉兰之间的一个自然杂交区进行了研究，这两种眉兰共享莫里熊蜂作为传粉者。还使用扩增片段长度多态性（AFLP）标记估计了杂交区的遗传结构，并通过控制杂交估计了同域分布区中两个亲本物种及其杂种的授粉适合度和结实率。
尽管杂种在唇瓣形态和非活性气味化合物方面介于亲本物种之间，但亲本物种和杂种在活性化合物方面产生的气味组合相似。然而，杂种产生的果实和种子数量明显低于亲本物种，并且杂交区的遗传结构表明它们大多是第一代杂种。
由于传粉者重叠和较弱的机械隔离，两个亲本物种在同域发生杂交，但合子后障碍降低了杂种频率和适合度，并阻止了广泛的基因渗入。这些结果突出了后期交配后障碍（如染色体分歧）对维持生殖隔离的重大贡献，而在一个通常认为交配前障碍占主导的兰花类群中。
