Data from: Seasonal changes in pollen limitation and femaleness along the snowmelt gradient in a distylous alpine herb, Primula modesta

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, Primula modesta, 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 P. modesta were examined during the flowering period. The pin and thrum plants of P. modesta 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（flowering phenology）强烈受融雪时间调控，广布植物的传粉环境在其花期内差异显著。本研究以二型花柱高山草本植物朝鲜报春（Primula modesta）为对象，在自然条件下沿融雪梯度（snowmelt gradient）调查其繁殖成功率，并与人工传粉实验（artificial pollination experiments）结果进行对比。此外，本研究还调查了朝鲜报春花期内的传粉者组成及其访花频率。同一生境下的朝鲜报春长花柱型（pin）与短花柱型（thrum）植株，若柱头表面获得足量的亲和花粉（legitimate pollen grains），其结籽能力并无差异。但在自然条件下，二者的结籽成功率往往（即便并非总是）受限于花粉限制（pollen limitation），且其功能性别（functional gender）分别偏向雌性与雄性，这与其生长生境相关。这些变异并非由资源限制（resource limitation）或型比例（morph ratio）偏倚导致，而是源于传粉环境的季节变化：传粉者类群从长舌型向短舌型更替，引发了从长雄蕊（短花柱型植株）到长花柱（长花柱型植株）的单向花粉传递。这种功能性别特化可能促进花柱异长（heterostyly）向雌雄异株（dioecy）的演化，但严重的花粉限制可能导致花柱异长向同型花柱（homostyly）瓦解。为阐明花柱异长植物的演化路径，我们需要积累更多实证数据（empirical data），以明确植物与传粉者间的物候同步性是如何确立的，以及该关系在多年间的稳定程度，同时还需估算单株植物的选择作用（selection）与基因流（gene flow）。