Koski Matthew H, Ashman Tia-Lynn
Ecology. 2015 Dec;96(12):3343-53. doi: 10.1890/15-0242.1.
Spatial variation in pollinator communities or behaviors can underlie floral diversification. Floral traits in the UV spectrum are common and mediate plant-pollinator interactions, but the role of pollinators in driving or maintaining their geographic variation has not been fully explored. We identify an altitudinal cline of increasing relative size of the UV bullseye pattern in Argentina anserina (Rosaceae) flowers, and assess whether pollination context contributes to clinal variation. At four sites that varied in altitude, we document the pollinator assemblage, and pollinator preference and visitation behavior. We then determine how pollinator visits affected pollen receipt and export. Finally, we describe how the functional relationship between UV floral phenotype and pollen receipt changed with altitude. Floral UV bullseye size increased with altitude, which corresponded with a change from a hymenopteran- to a dipteran-dominated pollinator assemblage. While dipteran and hymenopteran preferences for bullseye size were similar, flowers with large bullseyes received more foraging visits than those with small bullseyes at higher altitude. The reverse was observed at the lower altitudes; pollinators approached large-bullseye flowers often but rarely foraged. These differences are expected to affect fitness because foraging visits increased pollen export and receipt. Indeed, when natural variation in bullseye size was considered, it had a stronger effect on pollen receipt than other traits (flower size, display, or color). Plants with larger bullseyes tended to receive more pollen at the highest-altitude site, while those with smaller ones received more pollen at the lowest-altitude site. Results suggest that altitudinal changes in preference and behavior of the overall pollinator assemblage, but not differential preferences of pollinator taxonomic groups, could contribute to clinal variation in a UV floral trait for a generalist-pollinated plant.
传粉者群落或行为的空间变异可能是花卉多样化的基础。紫外光谱中的花部性状很常见，并介导植物与传粉者的相互作用，但传粉者在驱动或维持其地理变异方面的作用尚未得到充分探索。我们在鹅绒委陵菜（蔷薇科）花朵中发现了紫外靶心图案相对大小随海拔升高的梯度变化，并评估授粉环境是否有助于这种梯度变化。在四个海拔不同的地点，我们记录了传粉者组合、传粉者偏好和访花行为。然后我们确定传粉者的访花如何影响花粉接收和输出。最后，我们描述了紫外花部表型与花粉接收之间的功能关系如何随海拔变化。花的紫外靶心大小随海拔升高而增加，这与传粉者组合从以膜翅目为主转变为以双翅目为主相对应。虽然双翅目和膜翅目对靶心大小的偏好相似，但在较高海拔地区，具有大靶心的花朵比具有小靶心的花朵接受更多的觅食访花。在较低海拔地区观察到相反的情况；传粉者经常接近大靶心的花朵，但很少觅食。这些差异预计会影响适合度，因为觅食访花增加了花粉输出和接收。事实上，当考虑靶心大小的自然变异时，它对花粉接收的影响比其他性状（花大小、展示或颜色）更强。在最高海拔地点，具有较大靶心的植物往往接收更多花粉，而在最低海拔地点，具有较小靶心的植物接收更多花粉。结果表明，总体传粉者组合的偏好和行为的海拔变化，而非传粉者分类群的差异偏好，可能导致了一种泛化传粉植物紫外花部性状的梯度变化。
