Sterols are essential nutrients for bees which are thought to obtain them exclusively from pollen. It is possible that variability in pollen sterol content shapes pollinator-flower relationships, as bee species require the physiological capacity or behavioral adaptations to cope with unfavorable sterolic composition of pollen. One behavioral adaptation used by generalist bees to avoid deficiencies is the mixing of different pollen types from multiple botanical families to achieve an optimal nutritional balance. However, a possible strategy that has never been investigated is the specific addition of nutrients by adult bees to pollen during foraging trips. Here, we analyzed the pollen sterols from 48 plant species and assessed their relation with the level of bee dietary specialization. We also investigated whether sterol addition or modification might occur during pollen collection by comparing hand- and bee-collected pollen for nine bee species. Our results show that sterolic composition tends to be similar within the same plant family, but there was no impact of overall relatedness. For pollen sterol content and bee specialization, pollen from plants used by specialist bees displayed more uncommon sterols than pollen from plants used by generalist bees. In addition, a sterol addition behavior may occur during foraging trips and could be considered a possible strategy to balance nutrient deficiencies. Such behavior was unrelated to bee specialization as this phenomenon was observed in both the generalist Apis mellifera and specialist Dasypoda hirtipes , suggesting that sterols might constitute a physiological constraint even for specialist species.

中文翻译：

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蜜蜂采集花粉期间添加甾醇：平衡营养缺乏的另一种可能策略？

甾醇是蜜蜂必需的营养物质，被认为只能从花粉中获取。花粉甾醇含量的可变性可能会影响传粉者-花的关系，因为蜜蜂物种需要生理能力或行为适应来应对不利的花粉甾醇成分。通才蜜蜂为避免缺陷而使用的一种行为适应是混合来自多个植物科的不同花粉类型，以实现最佳营养平衡。然而，一种从未被研究过的可能策略是成年蜜蜂在觅食过程中向花粉中添加特定的营养物质。在这里，我们分析了 48 种植物的花粉甾醇，并评估了它们与蜜蜂饮食专业化水平的关系。我们还通过比较手工和蜜蜂收集的九种蜜蜂的花粉，研究了在花粉收集过程中是否会发生甾醇添加或修饰。我们的结果表明，同一植物科内的甾醇组成往往相似，但总体相关性没有影响。对于花粉甾醇含量和蜜蜂专业化，专业蜜蜂使用的植物花粉显示出比多才多艺蜜蜂使用的植物花粉更罕见的甾醇。此外，在觅食过程中可能会出现添加甾醇的行为，可以将其视为平衡营养缺乏的一种可能策略。这种行为与蜜蜂的专业化无关，因为这种现象在通才的蜜蜂和专科的黑头蜂中都观察到了，