Data from: Divergence in style length and pollen size leads to a postmating-prezygotic reproductive barrier among populations of Silene latifolia

A central tenet of speciation research is the need to identify reproductive isolating barriers. One approach to this line of research is to identify the phenotypes that lead to reproductive isolation. Several studies on flowering plants have shown that differences in style length contribute to reproductive isolation between species, leading us to consider whether style length could act as a reproductive barrier among populations of a single species. This could occur if style length varied sufficiently and pollen size covaried with style length. Populations of Silene latifolia exhibit variation in flower size, including style length, that is negatively correlated with annual precipitation. We show that this divergence in style length has a genetic basis and acts as a reproductive barrier: males from small-flowered populations produced relatively small pollen grains that were poor at fertilizing ovules when crossed to females from large-flowered populations, leading to a significant reduction in seed production. Manipulating the distance pollen tubes had to travel revealed that this failure was purely mechanical and not the result of other incompatibilities. These results show that style length acts as a postmating-prezygotic reproductive barrier and indicate a potential link between ecotypic differentiation and reproductive isolation within a species.

物种形成研究的核心信条之一，便是识别生殖隔离屏障 (reproductive isolating barriers)。该领域的一类研究思路为：识别可引发生殖隔离的表型特征。已有多项针对开花植物的研究表明，花柱长度 (style length) 的差异可促成物种种间的生殖隔离，这促使我们思考：花柱长度是否可在同一物种种群间充当生殖隔离屏障。若花柱长度存在足够显著的变异，且花粉大小与花柱长度存在协变关系，则该情形即可成立。麦瓶草 (Silene latifolia) 种群展现出花部尺寸的变异，包括花柱长度，且该变异与年降水量呈负相关。本研究证实，花柱长度的分化具有遗传基础，且可充当生殖隔离屏障：来自小花种群的雄性个体所产生的花粉粒相对较小，当与大花种群的雌性个体杂交时，此类花粉难以完成胚珠受精，进而导致种子产量显著下降。通过调控花粉管需生长的距离开展实验，结果表明该受精失败纯粹为机械性障碍，而非其他不相容机制所致。上述研究结果表明，花柱长度可作为交配后合子前 (postmating-prezygotic) 生殖隔离屏障，同时揭示了同一物种种群内生态型分化 (ecotypic differentiation) 与生殖隔离之间存在潜在关联。