Data from: Selection on Polemonium brandegeei (Polemoniaceae) flowers under hummingbird pollination: in opposition, parallel, or independent of selection by hawkmoths?

Particular floral phenotypes are often associated with specific groups of pollinators. However, flowering plants are often visited, and may be effectively pollinated by more than one type of animal. Therefore, a major outstanding question in floral biology asks: what is the nature of selection on floral traits when pollinators are diverse? This study examined how hummingbirds selected on the floral traits of Polemonium brandegeei, a species pollinated by both hummingbirds and hawkmoths. In array populations of P. brandegeei, we measured pollen movement, and female (seeds set) and male (seeds sired) fitness under hummingbird pollination. We then compared the patterns of selection by hummingbirds with our previous study examining selection by hawkmoths. We documented contrasting selection on sex organ positioning through female function, with hummingbirds selecting for stigmas exserted beyond the anthers and hawkmoths selecting for stigmas recessed below the anthers. Furthermore, hummingbirds selected for longer and wider corolla tubes, and hawkmoths selected for narrower corolla tubes. Therefore, contrasting selection by hawkmoths and hummingbirds may account for variation in sex organ arrangements and corolla dimensions in P. brandegeei. We documented how floral traits under selection by multiple pollinators can result in either an intermediate “compromise” between selective pressures (sex organs) or apparent specialization (corolla tube length) to one pollinator.特定的花部表型通常与特定的传粉者类群相关联。然而，开花植物往往会被多种动物造访，且可能被多种动物有效传粉。因此，花生物学领域一个悬而未决的核心问题是：当传粉者类群多样时，花部性状所承受的选择作用本质为何？本研究针对同时被蜂鸟（hummingbirds）和天蛾（hawkmoths）传粉的布兰德吉花荵（Polemonium brandegeei），探究了蜂鸟对其花部性状的选择作用。在布兰德吉花荵的实验种群中，我们测定了蜂鸟传粉条件下的花粉运动情况，以及雌性适合度（结籽数）与雄性适合度（父本结实数）。随后，我们将蜂鸟的选择模式与此前研究中天蛾的选择模式进行了对比。我们发现通过雌性功能介导的性器官位置选择存在显著差异：蜂鸟倾向于选择柱头（stigma）伸出花药（anther）之上的个体，而天蛾则倾向于选择柱头凹陷于花药下方的个体。此外，蜂鸟对更长更宽的花冠管（corolla tube）存在选择倾向，而天蛾则偏好更窄的花冠管。因此，天蛾与蜂鸟之间存在差异的选择作用，或许可以解释布兰德吉花荵在性器官排列方式与花冠管尺寸上的变异。本研究阐明了受多种传粉者选择的花部性状，既可能在选择压力下形成介于两者之间的“折中”表型（如性器官位置），也可能演化出对某一类传粉者的特化表型（如花冠管长度）。