Kameyama Yoshiaki, Watanabe Manami, Kurosawa Hideki, Nishimori Takuya, Matsue Daisuke, Takyu Masaaki
Faculty of Regional Environment Science Tokyo University of Agriculture Tokyo 156-8502 Japan.
Present address: OTA Floriculture Auction Co., Ltd. Tokyo 143-0001 Japan.
Ecol Evol. 2015 Oct 30;5(22):5352-5363. doi: 10.1002/ece3.1803. eCollection 2015 Nov.
Flowering phenology of alpine plants is strongly determined by the timing of snowmelt, and the conditions of pollination of widely distributed plants vary greatly during their flowering season. We examined the reproductive success of the distylous alpine herb, , along the snowmelt gradient under natural conditions, and compared it with the result of artificial pollination experiments. In addition, the compositions and visit frequencies of pollinators to the flower of were examined during the flowering period. The pin and thrum plants of growing at the same site have an equal ability to produce seeds if a sufficient amount of legitimate pollen grains are deposited on the stigma surface. However, under natural conditions, their seed-set success was often (even if not always) restricted by pollen limitation, and the functional gender of the pin and thrum plants biased to the female and male, respectively, associated with their growing sites. These variations were not ascribed to resource limitation nor biased morph ratio but to the seasonal changes in pollination situations, a replacement of pollinator types from long- to short-tongued pollinators resulted in unidirectional pollen transfer from long stamens (thrum plants) to long styles (pin plants). The functional gender specialization may enhance the evolution of dioecy from heterostyly, but the severe pollen limitation may cause the breakdown of heterostyly into homostyly. To consider the evolutionary pathway of heterostylous plants, an accumulation of the empirical data is required demonstrating how phenological synchrony between plants and pollinators is decided and to what degree this relationship is stable over years, along with estimates of selection and gene flow in individual plants.
高山植物的开花物候很大程度上由融雪时间决定，广泛分布的植物在其开花季节的授粉条件差异很大。我们在自然条件下沿着融雪梯度研究了二型花柱高山草本植物的繁殖成功率，并将其与人工授粉实验结果进行了比较。此外，在开花期还对该植物花朵的传粉者组成和访花频率进行了研究。生长在同一地点的该植物的长柱型和短柱型植株，如果有足够数量的合法花粉粒落在柱头表面，它们产生种子的能力是相等的。然而，在自然条件下，它们的结实成功率常常（即使并非总是）受到花粉限制，长柱型和短柱型植株的功能性别分别偏向雌性和雄性，这与它们的生长地点有关。这些差异并非归因于资源限制或形态比例偏差，而是由于授粉情况的季节性变化，传粉者类型从长舌型向短舌型的更替导致花粉从长雄蕊（短柱型植株）单向转移到长花柱（长柱型植株）。功能性别特化可能会促进从异型花柱向雌雄异株的进化，但严重的花粉限制可能会导致异型花柱分解为同型花柱。为了考虑异型花柱植物的进化途径，需要积累实证数据，以证明植物与传粉者之间的物候同步是如何决定的，以及这种关系在多年间的稳定程度，同时还需要估计个体植物中的选择和基因流动情况。
