Data from: Pollinator specificity drives strong prepollination reproductive isolation in sympatric sexually deceptive orchids

Few studies have quantified the full range of pre– and postzygotic barriers that limit introgression between closely related plant species. Here we assess the strength of four isolating mechanisms operating between two morphologically similar and very closely related sympatric orchid taxa, Chiloglottis valida and C. aff. jeanesii. Each taxon sexually attracts its specific wasp pollinator via distinct floral volatile chemistry. Behavioral experiments with flowers and synthetic versions of their floral volatiles confirmed that very strong pollinator isolation is mediated by floral odor chemistry. However, artificially placing flowers of the two taxa in contact proximity revealed the potential for rare interspecific pollination. Although we found hybrid vigour in F1 hybrids produced by hand-crossing , genetic analysis at both nuclear and chloroplast loci showed significant and moderate to strong genetic differentiation between taxa. A Bayesian clustering method for the detection of introgression at nuclear loci failed to find any evidence for hybridization across 571 unique genotypes at one site of sympatry. Rather than inhibiting gene flow, postpollination barriers surveyed here show no contribution to overall reproductive isolation. This demonstrates the primacy of pollinators in maintaining species boundaries in these orchids, which display one of the strongest known examples of prepollination floral isolation.

目前鲜有研究量化限制近缘植物类群间基因渐渗（introgression）的全套合子前与合子后生殖障碍。本研究针对两个形态相似、亲缘关系极近的同域兰科类群——Chiloglottis valida与C. aff. jeanesii，评估了四种隔离机制的作用强度。两类群均通过独特的花香挥发物成分，以性拟态方式吸引各自专属的传粉胡蜂。针对鲜花及其花香挥发物合成模拟物的行为实验证实，极强的传粉者隔离由花香气味介导。然而，将两类群的花朵人工置于近距离接触后，发现存在罕见的种间传粉潜力。尽管人工杂交获得的F1代杂种表现出杂种优势（hybrid vigour），但核基因座与叶绿体基因座的遗传分析显示，两类群间存在显著且中等至强度的遗传分化。针对核基因座渐渗检测的贝叶斯聚类法，在该同域分布样地的571个独特基因型中未发现任何杂交证据。本研究所调查的传粉后障碍非但未抑制基因流，反而对整体生殖隔离（reproductive isolation）无任何贡献。这表明，在这类兰科植物中，传粉者在维持物种边界方面占据主导地位——这类兰科也是目前已知传粉前花香隔离效应最强的类群之一。