Plants exhibit a wide array of floral forms and pollinators can act as agent of selection on floral traits. Two trends have emerged from recent reviews of pollinator-mediated selection in plants. First, pollinator-mediated selection on plant-level attractants such as floral display size is stronger than on flower-level attractant such as flower color. Second, when comparing plant species, distinct pollinators can exert different selection patterns on floral traits. In addition, many plant species are visited by a diverse array of pollinators but very few studies have examined selection by distinct pollinators. In the current study, we examined phenotypic selection on flower color and floral display size by three distinct bee species, the European honey bee, Apis mellifera, the common eastern bumble bee, Bombus impatiens, and the alfalfa leafcutting bee, Megachile rotundata, foraging on Medicago sativa. To estimate phenotypic selection by each bee species and for all bees combined simultaneously and on the same group of plants, we introduce a new method that combines pollinator visitation data to seed set and floral trait measurements data typical of phenotypic selection study. When comparing floral traits, all bee species selected on the number of racemes per stem and the number of stems per plant, two components of floral display size. However, only leafcutting bees selected on hue or flower color and only bumble bees selected on chroma or darkness of flowers. Selection on chroma occurred via correlational selection between chroma and number of open flowers per raceme and we examine how correlational selection may facilitate the evolution of flower color in plant populations. When comparing bee species, the three bee species exerted similar selection pattern on some floral traits but different patterns on other floral traits and differences in selection patterns were observed between flower-level and plant-level attractants. The trends detected were consistent with previous studies and we advocate the approach introduced here for future studies examining the impact of distinct pollinators on floral trait evolution.

植物表现出各种各样的花卉形态，授粉媒介可以作为选择性状的媒介。最近对植物中授粉媒介介导选择的评论出现了两种趋势。首先，授粉媒介对植物水平引诱剂（如花卉展示尺寸）的选择要强于对花朵水平引诱剂（如花朵的颜色）的选择。其次，当比较植物物种时，不同的传粉者可以对花性状施加不同的选择模式。此外，各种各样的传粉媒介访问了许多植物物种，但是很少有研究检查不同传粉媒介的选择。在目前的研究中，我们研究了三种不同的蜜蜂（欧洲蜜蜂，蜜蜂，常见的东部大黄蜂， 熊熊凤仙花以及苜蓿切叶蜂， 超级轮虫，觅食 紫花苜蓿。为了估计每种蜜蜂物种以及同时在同一植物群上组合的所有蜜蜂的表型选择，我们引入了一种新方法，该方法将授粉媒介访视数据结合到表型选择研究中典型的种子集和花性状测量数据中。比较花性状时，选择的所有蜜蜂物种均取决于每茎的总消旋体数和每株植物的茎数，这是花卉展示大小的两个组成部分。但是，只能选择色调或花朵颜色的切叶蜜蜂，而只能选择色度或花朵暗度的大黄蜂。色度的选择是通过色度与每个总状花序开放花朵数量之间的相关选择而发生的，我们研究了相关选择如何促进植物群体中花朵颜色的演变。比较蜂种时 这三种蜜蜂在某些花性状上表现出相似的选择模式，但在其他花性状上表现出不同的模式，并且在花水平和植物水平引诱剂之间观察到选择模式的差异。检测到的趋势与以前的研究一致，我们提倡将此处介绍的方法用于未来的研究，以研究不同传粉媒介对花性状演变的影响。