Data from: Selection on floral design in Polemonium brandegeei (Polemoniaceae): female and male fitness under hawkmoth pollination

Plant-pollinator interactions promote the evolution of floral traits that attract pollinators and facilitate efficient pollen transfer. The spatial separation of sex-organs, herkogamy, is believed to limit sexual interference in hermaphrodite flowers. Reverse herkogamy (stigma recessed below anthers) and long narrow corolla-tubes are expected to promote efficiency in male function under hawkmoth pollination. We tested this prediction by measuring selection in six experimental arrays of Polemonium brandegeei, a species that displays continuous variation in herkogamy, resulting in a range of recessed to exserted stigmas. Under glasshouse conditions, we measured pollen removal and deposition, and estimated selection gradients (ß) through female fitness (seeds set) and male fitness (siring success based on 6 polymorphic microsatellite loci). Siring success was higher in plants with more nectar sugar and narrow corolla-tubes. However, selection through female function for reverse herkogamy was considerably stronger than was selection through male function. Hawkmoths were initially attracted to larger flowers, but overall preferred plants with reverse herkogamy. Greater pollen deposition and seed set also occurred in reverse herkogamous plants. Thus, reverse herkogamy may be maintained by hawkmoths through female rather than male function. Further, our results suggest that pollinator attraction may play a considerable role in enhancing female function.

植物与传粉者的互作可驱动花部性状演化，这类性状能够吸引传粉者并促进高效的花粉传递。学界普遍认为，雌雄器官的空间分离——雌雄异位（herkogamy）——可限制雌雄同体花内的性干扰。反向雌雄异位（柱头凹陷于花药下方）与狭长的花冠筒，被认为可在天蛾传粉情境下提升雄性功能效率。本研究以布兰登格花荵（Polemonium brandegeei）为研究材料，该物种的雌雄异位程度存在连续变异，涵盖柱头从凹陷到伸出的全部表型范围；我们通过6个实验阵列开展选择作用检测，以此验证前述预测。在温室条件下，我们测定了花粉移除与花粉沉积量，并通过雌性适合度（结实种子数）与雄性适合度（基于6个多态性微卫星位点的父本成功率）估算了选择梯度（ß）。结果显示，花蜜糖含量更高、花冠筒更狭长的植株，其父本成功率也更高。然而，针对反向雌雄异位的雌性功能选择强度，显著高于雄性功能选择。天蛾最初会被更大的花朵吸引，但整体上更偏好具有反向雌雄异位的植株；这类植株的花粉沉积量与结实率也更高。由此可见，天蛾或通过雌性功能而非雄性功能维持反向雌雄异位性状。此外，本研究结果表明，传粉者吸引在提升雌性功能方面或发挥着重要作用。