Premise of research. In plants, evolutionary shifts from one pollinator guild to another are normally associated with coordinated changes of several floral characters. These might be floral morphology, color, and scent. On the basis of the animals’ different sizes and shapes as well as their visual and olfactory sensitivities or preferences, floral visitors exert different selective pressures on flowers. Floral traits might act as floral filters, attracting pollinators or excluding unwanted flower visitors. We use the genus Salvia, in which several shifts from bee to bird pollination are known, to examine the potential role of floral color versus floral construction as floral filters. Methodology. We studied 26 bee-pollinated, 30 bird-pollinated, and 3 intermediate Salvia species. Besides documenting floral morphology and floral guides, we measured floral spectral reflectance and characterized the flowers’ perception by bees. Pivotal results. The color loci of half of the bird-pollinated species (red to humans) are in the achromatic center and thus are less conspicuous to bees. All other species (mostly bluish) have significantly greater color contrast and spectral purity and can be recognized by bees and birds. Nectar guides occurred in almost all bee-pollinated species included in the study but in no bird-pollinated species. The results suggest that color might play a role as a floral filter against bees in only half of the bird-pollinated species, while mechanical bee exclusion appears to be important in all bird-pollinated species. Conclusions. Our data indicate that bees are excluded from bird-pollinated flowers mainly by floral construction. The red color and the absence of nectar guides in bird-pollinated flowers can be interpreted as adaptations for reducing nectar and pollen theft by bees via visual exclusion without losing attractiveness for birds.

中文翻译：

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鸟授粉丹参花中的蜜蜂排除——花色与花结构的作用

研究的前提。在植物中，从一个传粉者行会到另一个传粉者行会的进化转变通常与几个花卉特征的协调变化有关。这些可能是花的形态、颜色和气味。根据动物的不同大小和形状以及它们的视觉和嗅觉敏感性或偏好，花卉游客对花卉施加不同的选择压力。花卉特征可能充当花卉过滤器，吸引传粉者或排除不受欢迎的花卉访客。我们使用鼠尾草属，其中已知从蜜蜂授粉到鸟类授粉的几种转变，以检查花卉颜色与花卉结构作为花卉过滤器的潜在作用。方法。我们研究了 26 种蜜蜂授粉、30 种鸟类授粉和 3 种中间鼠尾草物种。除了记录花卉形态和花卉指南，我们测量了花的光谱反射率，并表征了蜜蜂对花的感知。关键结果。一半的鸟类授粉物种（对人类为红色）的颜色位点位于消色差中心，因此对蜜蜂不那么显眼。所有其他物种（主要是蓝色）具有明显更高的颜色对比度和光谱纯度，并且可以被蜜蜂和鸟类识别。花蜜向导发生在研究中几乎所有蜜蜂授粉的物种中，但没有鸟类授粉的物种。结果表明，颜色可能仅在一半的鸟类授粉物种中起到过滤蜜蜂的作用，而机械排除蜜蜂似乎在所有鸟类授粉物种中都很重要。结论。我们的数据表明，蜜蜂主要通过花结构被排除在鸟类授粉的花朵之外。