Data from: Effect of expanded variation in anther position on pollinator visitation to wild radish, Raphanus raphanistrum

Background and Aims: Plant-pollinator interactions shape the evolution of flowers. Floral attraction and reward traits have often been shown to affect pollinator behavior, but the possible effect of efficiency traits on visitation behavior has rarely been addressed. Here we tested for the effect of anther position, usually considered a trait that influences efficiency of pollen deposition on pollinators, on pollinator visitation rates and visit duration in flowers of wild radish, Raphanus raphanistrum. Methods: We used artificial selection lines from two experiments that expanded the naturally-occurring phenotypic variation in anther position. In one experiment, plant lines were selected to either increase or decrease anther exsertion. The other experiment decreased anther dimorphism, which resulted in increased short stamen exsertion. We hypothesized that increased exsertion will increase visitation of pollen foragers due to increased visual attraction. We also hypothesized that exsertion of anthers above the corolla would interfere with nectar foragers and increase time of visit per flower. Key Results: In the exsertion selection experiment, increased exsertion of both short and long stamens resulted in an increased number of fly visits per plant, and in the dimorphism experiment bee visits increased with increased short stamen exsertion. Duration of nectar feeders declined significantly with increasing long stamen exsertion, as opposed to the hypothesis. Conclusions and synthesis: Until now, anther position was considered an efficiency trait to enhance pollen uptake and deposition. We show that anther position in wild radish has an ecological significance also in attracting pollen foragers. This study suggests an additional adaptive role for anther position beyond efficiency, and highlights the multiple ecological functions of floral traits in plant-pollinator interactions.

研究背景与目的：植物-传粉者互作塑造了花的演化。既往研究已多次证实，花的吸引性与回报性状会影响传粉者行为，但效率性状对传粉者造访行为的潜在影响却极少被关注。本研究以野萝卜（Raphanus raphanistrum）为研究对象，检验了通常被认为可影响花粉在传粉者身上沉积效率的花药位置，对其造访频率与单次造访时长的影响。
研究方法：我们利用两项实验的人工选择品系，以扩大野萝卜自然存在的花药位置表型变异。其中一项实验中，我们通过人工选择提升或降低了花药伸出度；另一项实验则降低了花药二态性，进而提升了短雄蕊的伸出度。我们提出两项假说：一是提升伸出度可通过增强视觉吸引，增加花粉采食者的造访频次；二是花冠上方的花药伸出会干扰花蜜采食者，并延长单花造访时长。
主要结果：在花药伸出度选择实验中，短雄蕊与长雄蕊的伸出度提升均使单株植物的蝇类造访次数显著增加；而在花药二态性实验中，短雄蕊伸出度提升则使蜂类造访次数增加。与原假说相反，随着长雄蕊伸出度升高，花蜜采食者的单次造访时长显著下降。
结论与综合分析：迄今为止，花药位置一直被视为提升花粉获取与沉积效率的效率性状。本研究表明，野萝卜的花药位置在吸引花粉采食者方面同样具有生态意义。本研究揭示了花药位置除提升效率外的额外适应性功能，并凸显了花性状在植物-传粉者互作中所具备的多重生态功能。