Baena-Díaz F, Fornoni J, Sosenski P, Weller S G, Domínguez C A
Departamento de Ecología Evolutiva, Instituto de Ecología, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA.
Plant Biol (Stuttg). 2017 Nov;19(6):994-1002. doi: 10.1111/plb.12615. Epub 2017 Sep 18.
Pollen and stigma size have the potential to influence male fitness of hermaphroditic plants, particularly in species presenting floral polymorphisms characterised by marked differences in these traits among floral morphs. In this study, we take advantage of the evolutionary transition from tristyly to distyly experienced by Oxalis alpina (Oxalidaceae), and examined whether modifications in the ancillary traits (pollen and stigma size) respond to allometric changes in other floral traits. Also, we tested whether these modifications are in accordance with what would be expected under the hypothesis that novel competitive scenarios (as in distylous-derived reproductive system) exert morph- and whorl-specific selective pressures to match the available stigmas. We measure pollen and stigma size in five populations of O. alpina representing the tristyly-distyly transition. A general reduction in pollen and stigma size occurred along the tristyly-distyly transition, and pollen size from the two anther levels within each morph converged to a similar size that was characterised by whorl-specific changes (increases or decreases) in pollen size of different anthers in each floral type. Overall, results from this study show that the evolution of distyly in this species is characterised not only by changes in sexual organ position and flower size, but also by morph-specific changes in pollen and stigma size. This evidence supports the importance of selection on pollen and stigma size, which increase fitness of remaining morphs following the evolution of distyly, and raises questions to explore on the functional value of pollen size in heterostylous systems under pollen competition.
花粉和柱头大小有可能影响雌雄同体植物的雄性适合度，尤其是在呈现花部多态性的物种中，这些物种的花部形态在这些性状上存在显著差异。在本研究中，我们利用了高山酢浆草（酢浆草科）从三型花柱向二型花柱的进化转变，并研究了附属性状（花粉和柱头大小）的变化是否响应其他花部性状的异速生长变化。此外，我们还测试了这些变化是否符合以下假设所预期的情况：新的竞争场景（如在衍生自二型花柱的生殖系统中）会施加特定形态和轮的选择压力，以匹配可用的柱头。我们测量了代表三型花柱 - 二型花柱转变的五个高山酢浆草种群的花粉和柱头大小。沿着三型花柱 - 二型花柱的转变，花粉和柱头大小普遍减小，并且每个形态内两个花药水平的花粉大小收敛到相似的大小，其特征是每种花型中不同花药的花粉大小存在特定轮的变化（增加或减少）。总体而言，本研究结果表明，该物种中二型花柱的进化不仅以性器官位置和花大小的变化为特征，还以花粉和柱头大小的特定形态变化为特征。这一证据支持了对花粉和柱头大小进行选择的重要性，这种选择在二型花柱进化后增加了其余形态的适合度，并提出了在花粉竞争下异花柱系统中花粉大小的功能价值有待探索的问题。
