Premise of research. Bat-pollinated flowers have wide morphologies and produce copious and diluted nectar that commonly spills from flowers. Considering that sugar concentration modulates rheological properties in aqueous solutions, we estimated its role in regulating nectar retention. Methodology. We took three bat-pollinated species with open floral morphologies (Calliandra aeschynomenoides; Hymenaea cangaceira, Fabaceae; and Tarenaya longicarpa, Cleomaceae) as models. We evaluated how sugar concentration affects their nectar retention through experiments with artificial nectar in different sugar percentages. We also reported the volume and concentration of sugar in the nectar drops of these flowers under natural conditions. Pivotal results. Depending on the plant species, higher sugar concentration can improve nectar retention, reduce it, or even present intermediate values that enable the retention of larger nectar volumes. Nevertheless, sugar concentrations from flowers in the field do not coincide with those that allow a greater accumulation of nectar, and flowers retain smaller volumes than recorded in experiments. Conclusions. Peculiarities of each flower (e.g., size, thickness, and quantities of structures available for nectar adhesion) ensure distinct effects from sugar concentration on nectar retention. Even so, it seems that there is no strategy from plants to prevent spillage of nectar by regulating the sugar concentration. Shifts in the sugar concentration of nectar may influence other aspects of the pollination biology of the species. Spilling part of the produced nectar, despite seeming to be a paradoxical waste of resources, can be a less impactful factor.

中文翻译：

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蝙蝠授粉花朵的“甜雨”：糖浓度如何调节花蜜保留？

研究的前提。蝙蝠授粉的花具有广泛的形态，并产生通常从花中溢出的大量稀释的花蜜。考虑到糖浓度调节水溶液中的流变特性，我们估计了它在调节花蜜保留中的作用。方法。我们采用了三种具有开放花卉形态的蝙蝠授粉物种（Calliandra aeschynomenoides；Hymenaea cangaceira，豆科；和Tarenaya longicarpa，Cleomacaceae）作为模型。我们通过不同糖百分比的人工花蜜实验评估了糖浓度如何影响它们的花蜜保留。我们还报告了在自然条件下这些花的花蜜滴中糖的体积和浓度。关键结果。根据植物种类，较高的糖浓度可以提高花蜜的保留率，减少花蜜，甚至提供中间值，以便保留更大的花蜜量。然而，田间花朵的糖浓度与允许更多花蜜积累的浓度不一致，花朵保留的体积比实验中记录的要小。结论。每朵花的特性（例如，大小、厚度和可用于花蜜粘附的结构数量）确保了糖浓度对花蜜保留的不同影响。即便如此，植物似乎没有通过调节糖浓度来防止花蜜溢出的策略。花蜜糖浓度的变化可能会影响该物种授粉生物学的其他方面。溢出部分生产的花蜜，尽管似乎是一种自相矛盾的资源浪费，但可能是一个影响较小的因素。