ow do the sterol requirements of bee species affect their pollen foraging choices?

近几十年来，在全球范围内观察到许多昆虫种群的数量下降，由于作物使用农药、疾病传播、寄生虫和土地利用变化，蜜蜂遭受了一些最大的损失（Potts et al., 2016）。花粉和花蜜等花卉食物资源的损失也被认为是蜜蜂数量下降的一个原因，蜜蜂种群的趋势反映了它们的花卉宿主的趋势（Biesmeijer等人，2006；Kleijn和Raemakers， 2008）。蜜蜂完全依赖花朵作为食物，成虫以花蜜为能量来源，花粉为幼虫提供主要食物来源。因此，这些资源的质量和类型直接影响到蜜蜂的生长和生存（Vanderplanck et al., 2014; Moermanet al., 2017），宿主可用性的变化直接影响蜜蜂的丰度和分布。大约75%的作物物种依赖动物授粉，其中蜜蜂占最大份额（Klein et al., 2007; Rader et al., 2016）。这项服务的成功维持在很大程度上依赖于我们对蜜蜂营养需求的理解，而这一点仍然很差。然而，我们确实知道，当只有劣质花粉时，幼虫的发育和存活率会大大降低（Genissel等人，2002；Moerman等人，2017）。因此，量化蜜蜂的营养需求和不同植物物种的供应能力在改善资源稀缺环境中的传粉者种植计划方面具有明确的应用价值，也是成功保护蜜蜂工作的关键。蜜蜂能够选择性地寻找营养上更喜欢的花粉（Somme etal., 2015; Vaudo etal., 2016； Vanderplanck等）。与花蜜相比，Goulson， D. and Dar, 2004; Goulson et al., 2005)更有针对性地采集花粉。花粉含有一系列重要的膳食氨基酸、脂质、维生素和蛋白质，不同物种的蜜蜂也有所不同（Roulston和Cane， 2000），但尤其是甾醇具有很高的种内变异（Villette等人，2015），并且对收集它们的蜜蜂具有高度特异性（Moerman等人，2017）。蜜蜂无法合成自己的固醇，因此饮食来源必须满足它们所有的生理需求（BehmerandNes,2003； Roulston和Cane， 2000）。因此，花粉选择可能受到这些要求的限制，这为不同物种的狭窄或灵活的觅食策略提供了潜在的解释。因此，分类群的特定营养需求和植物分布和丰度的变化可能是驱动某些传粉媒介种群波动的关键变量。关于花粉甾醇在蜜蜂多样性和丰度中的作用，存在主要的知识空白。我们不知道大多数蜜蜂物种对甾醇的需求，我们对花粉中甾醇多样性的了解也非常缺乏。我的工作将通过为在英国发现的蜜蜂和植物物种的新选择生成甾醇谱来解决这一缺陷，以回答以下问题：英国花粉甾醇资源的分布是否有助于解释蜜蜂多样性和丰度的模式？不同种类的大黄蜂对固醇的营养需求和觅食选择有何不同？推荐的以传粉媒介为目标的种子混合物是否提供了支持英国多样化蜜蜂群落所需的花粉营养多样性？花粉专家蜜蜂物种在不同的花卉景观中表现出保守的甾醇选择吗？

BackgroundIn recent decades there has been an observed global decline in many insect groups with bees experiencing some of the greatest losses as a result of pesticide usage on crops, spread of disease, parasites and changes in land use(Potts et al., 2016).Loss of floral food resources, such as pollen and nectar, has also been a suggested explanation for declines, with bee population trends mirroring those of their floral hosts (Biesmeijer et al., 2006; Kleijn and Raemakers, 2008).Bees are entirely dependent on flowers for food with adults consuming nectar for energy and pollen providing the main food source for larvae. The quality and type of these resources consequently has a direct impact on growth and survival (Vanderplanck et al., 2014; Moermanet al., 2017)and changes in host availability directly affect bee abundance and distribution. Approximately 75%ofcrop species are dependent on anima pollination with bees providing the largest share (Klein et al., 2007; Rader et al., 2016). Successful maintenance of this service is strongly reliant on our understanding of bees' nutritional needs which remains poor. We do however know that larval development and survival can be greatly reduced when only poor quality pollen is available (Genissel et al., 2002; Moerman et al., 2017). Quantifying bee nutritiona lrequirements and the provisioning abilities of different plant species therefore has clear applications in the improvement of pollinator planting schemes in resource scarce environments and will also be key to successful bee conservation efforts. Aims and objectives Bees are able to selectively forage for nutritionally preferred pollen (Somme et al., 2015; Vaudo et al., 2016; Vanderplanck etal., 2019)and visit a more targeted range of plants for pollen compared to nectar (Goulson, D. and Dar, 2004; Goulson et al., 2005).Pollen containsa range of important dietary amino acids, lipids, vitamins and proteins for bees that vary across species (Roulston and Cane, 2000)but sterols in particular have high intraspecies variation (Villette et al., 2015)and can be highly specific to the bees that collect them (Moerman et al., 2017). Bees are unable to synthesise their own sterols and dietary sources must therefore fulfil all their physiological requirements(BehmerandNes,2003; Roulston and Cane, 2000). Pollen choices could be, as a consequence, constrained by these requirements, providing a potential explanation for narrow or in flexible foraging strategies in different species. Taxon specific nutrient requirements and changes in plant distribution and abundance could therefore be a key variable driving fluctuations in certain pollinator populations. There are major knowledge gaps regarding the role of pollen sterols in bee diversity and abundance. We do not know the sterol requirements of most bee species and our knowledge of the diversity of sterols found in pollen is also critically lacking. My work will address this deficit by generating sterol profiles for a novel selection of both bee and plant species found in the UK to answer the following questions:Can the distribution of pollen sterol resources in the UK help explain patterns of bee diversity and abundance?How do sterol nutritional requirements and foraging choices differ across bumble bee species?Do recommended pollinator-targeted seed mixes provide the pollen nutritional diversity required to support diverse bee communities in the UK?Do pollen specialist bee species show conserved sterol selection across different floral landscapes?