Data from: Mismatch in the distribution of floral ecotypes and pollinators: insights into the evolution of sexually deceptive orchids

Plants are predicted to show floral adaptation to geographic variation in the most effective pollinator, potentially leading to reproductive isolation and genetic divergence. Many sexually deceptive orchids attract just a single pollinator species, limiting opportunities to experimentally investigate pollinator switching. Here we investigate Drakaea concolor, which attracts two pollinator species. Using pollinator choice tests, we detected two morphologically similar ecotypes within D. concolor. The common ecotype only attracted Zaspilothynnus gilesi, while the rare ecotype also attracted an undescribed species of Pogonothynnus. The rare ecotype occurred at populations nested within the distribution of the common ecotype, with no evidence of ecotypes occurring sympatrically. Surveying for pollinators at over 100 sites revealed that ecotype identity was not correlated with wasp availability, with most orchid populations only attracting the rare Z. gilesi. Using microsatellite markers, genetic differentiation among populations was very low (GST = 0.011) regardless of ecotype, suggestive of frequent gene flow. Taken together, these results may indicate that the ability to attract Pogonothynnus has evolved recently but this ecotype is yet to spread. The nested distribution of ecotypes, rather than the more typical formation of ecotypes in allopatry, illustrates that in sexually deceptive orchids pollinator switching could occur throughout a species’ range, resulting from multiple potentially suitable but unexploited pollinators occurring in sympatry. This unusual case of sympatric pollinators highlights D. concolor as a promising study system for further understanding the process of pollinator switching from ecological, chemical and genetic perspectives.

据预测，植物会演化出花部适应性以适应传粉者（pollinator）的地理变异，这可能引发生殖隔离与遗传分化。许多性欺骗兰（sexually deceptive orchids）仅会吸引单一传粉者物种，这限制了通过实验探究传粉者转换（pollinator switching）的可能性。本研究以同时吸引两种传粉者的同色锤兰（Drakaea concolor）为对象展开调查。通过传粉者选择实验，我们在同色锤兰中发现了两种形态相似的生态型（ecotype）：常见生态型仅能吸引吉莱氏脊唇泥蜂（Zaspilothynnus gilesi），而稀有生态型还可吸引一种尚未被描述的毛唇泥蜂属（Pogonothynnus）物种。稀有生态型的种群分布嵌套于常见生态型的分布范围之内，未发现两种生态型同域共存的证据。对100余个样地开展传粉者调查后发现，生态型类型与胡蜂可获得性并无关联，多数同色锤兰种群仅能吸引吉莱氏脊唇泥蜂。利用微卫星标记（microsatellite markers）分析显示，无论所属生态型如何，种群间的遗传分化程度均极低（GST=0.011），这提示种群间存在频繁的基因流（gene flow）。综合上述结果，本研究提示，吸引毛唇泥蜂属物种的能力是近期演化而来的，但该稀有生态型尚未完成扩散。生态型的嵌套分布模式（而非更为典型的异域分布（allopatry）下的生态型形成模式）表明，在性欺骗兰中，传粉者转换可在物种分布范围内的任意区域发生，这源于同域共存着多种潜在适宜但尚未被利用的传粉者。这一罕见的同域传粉者案例，将同色锤兰确立为极具潜力的研究系统，可用于从生态学、化学及遗传学视角进一步解析传粉者转换的过程。