Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
Biol Lett. 2013 Aug 14;9(5):20130495. doi: 10.1098/rsbl.2013.0495. Print 2013 Oct 23.
Differentiation of female sexual organs in flowering plants is rare and contrasts with the wide range of male reproductive strategies. An unusual example involves diplostigmaty, the possession of spatially and temporally distinct stigmas in Sebaea (Gentianaceae). Here, the single pistil within a flower has an apical stigma, as occurs in most flowering plants, but also a secondary stigma that occurs midway down the style, which is physically discrete and receptive several days after the apical stigma. We examined the function of diplostigmaty in Sebaea aurea, an insect-pollinated species of the Western Cape of South Africa. Floral manipulations and measurements of fertility and mating patterns provided evidence that basal stigmas function to enable autonomous delayed self-pollination, without limiting opportunities for outcrossing and thus avoiding the costs of seed discounting. We suggest that delayed selfing serves as a mechanism of reproductive assurance in populations with low plant density. The possession of dimorphic stigma function provides a novel example of a flexible mixed-mating strategy in plants that is responsive to changing demographic conditions.
在有花植物中，雌性生殖器官的分化较为罕见，这与广泛的雄性生殖策略形成鲜明对比。一个不寻常的例子是 Sebaea（龙胆科）中的二型柱头现象，即具有空间和时间上明显不同的柱头。在这种情况下，一朵花中的单个雌蕊既有位于顶端的柱头，就像大多数有花植物一样，又有位于花柱中部的二级柱头，二级柱头与顶端柱头在物理上是分开的，并且在几天后具有接受花粉的能力。我们研究了南非西开普省昆虫传粉的 Sebaea aurea 中这种二型柱头的功能。通过对花朵进行操作以及对育性和交配模式进行测量，我们提供了证据表明，基部柱头的功能是实现自主延迟自交，而不会限制异交的机会，从而避免了种子折价的成本。我们认为，延迟自交是在植物密度较低的种群中保证繁殖的一种机制。具有二态柱头功能的特性为植物提供了一个新的灵活的混合交配策略的例子，该策略对不断变化的人口统计条件有响应。
