Institute of Systematic Botany, University of Zurich, 8008 Zurich, Switzerland.
Ann Bot. 2012 Nov;110(6):1233-44. doi: 10.1093/aob/mcs199. Epub 2012 Sep 21.
Heterostyly is a floral polymorphism that has fascinated evolutionary biologists since Darwin's seminal studies on primroses. The main morphological characteristic of heterostyly is the reciprocal placement of anthers and stigmas in two distinct (distyly) floral morphs. Variation in the degree of intermorph sexual reciprocity is relatively common and known to affect patterns of pollen transfer within species. However, the partitioning of sexual organ reciprocity within and between closely related species remains unknown. This study aimed at testing whether intermorph sexual reciprocity differs within vs. between primrose species that hybridize in nature and whether the positions of sexual organs are correlated with other floral traits.
Six floral traits were measured in both floral morphs of 15 allopatric populations of Primula elatior, P. veris and P. vulgaris, and anther-stigma reciprocity was estimated within and between species. A combination of univariate and multivariate approaches was used to test whether positions of reproductive organs were less reciprocal between than within species, to assess correlations between sexual organ positions and other corolla traits, and to quantify differences between morphs and species.
The three species were morphologically well differentiated in most floral traits, except that P. veris and P. vulgaris did not differ significantly in sexual organ positions. Overall, lower interspecific than intraspecific sexual organ reciprocity was detected. This decrease was marked between P. elatior and P. vulgaris, intermediate and variable between P. elatior and P. veris, but negligible between P. veris and P. vulgaris.
Differences in anther and stigma heights between the analysed primrose species were of the same magnitude or larger than intraspecific differences that altered pollen flow within other heterostylous systems. Therefore, it is possible to suggest that considerable reductions of sexual organ reciprocity between species may lower interspecific pollen flow, with potential effects on reproductive isolation.
异型花柱是一种花卉多态性，自达尔文对报春花属植物进行开创性研究以来，一直吸引着进化生物学家的兴趣。异型花柱的主要形态特征是花药和柱头在两种不同的（二型花柱）花形态中相互置换。两性花形态之间的性互置程度的变化相对常见，并且已知会影响物种内的花粉转移模式。然而，在密切相关的物种内和物种之间，性器官的互置分配仍然未知。本研究旨在检验在自然杂交的报春花物种中，两性花形态内的互置程度是否与两性花形态之间不同，以及性器官的位置是否与其他花部特征相关。
在 15 个异域种群的报春花属植物的两性花形态中测量了 6 个花部特征，并估计了物种内和物种间的花药-柱头互置程度。采用单变量和多变量方法的组合，检验了生殖器官的位置在种间是否比种内更不互置，评估了性器官位置与其他花冠特征之间的相关性，以及量化了两性花形态和物种之间的差异。
除了 P. veris 和 P. vulgaris 在性器官位置上没有显著差异外，这三个物种在大多数花部特征上形态上差异明显。总体而言，种间的性器官互置程度低于种内。这种下降在 P. elatior 和 P. vulgaris 之间明显，在 P. elatior 和 P. veris 之间中等且多变，但在 P. veris 和 P. vulgaris 之间可以忽略不计。
分析的报春花物种之间的花药和柱头高度差异与改变其他异型花柱系统内花粉流的种内差异一样大或更大。因此，可以推测，物种间性器官互置程度的显著降低可能会降低种间花粉流，从而对生殖隔离产生潜在影响。
