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

背景近几十年来，观察到许多昆虫种群的数量在全球范围内下降，其中蜜蜂遭受的损失最大，原因是农作物上使用杀虫剂、疾病传播、寄生虫和土地利用的变化(Potts等人，2016)。花卉食物资源的丧失，如花粉和花蜜，也是减少的原因，蜜蜂的数量趋势反映了它们的花卉宿主(Biesmeijer等人，2006；Kleijn和Raemaker，2008)。蜜蜂完全依赖花卉作为食物，成年蜜蜂消耗花蜜作为能量，花粉是幼虫的主要食物来源。因此，这些资源的质量和类型对生长和生存有直接影响(Vanderplanck等人，2014；Moermanet等人，2017)，宿主可获得性的变化直接影响蜜蜂的丰度和分布。大约75%的作物物种依赖于动植物授粉，蜜蜂提供了最大的份额(Klein等人，2007年；Rader等人，2016)。这项服务的成功维持在很大程度上取决于我们对蜜蜂营养需求的了解，而蜜蜂的营养需求仍然很差。然而，我们确实知道，当只有质量较差的花粉可用时，幼虫的发育和存活会大大减少(Genissel等人，2002年；Moerman等人，2017年)。因此，量化不同植物种类的蜜蜂营养需求和供应能力在改进资源稀缺环境中的传粉者种植方案方面具有明显的应用价值，也将是成功的蜜蜂保护努力的关键。目的和目的蜜蜂能够有选择地寻找营养偏好的花粉(Somme等人，2015；Vaudo等人，2016；Vanderplanck等人，2019年)，并访问与花蜜相比更有针对性的植物范围的花粉(Goulson，D.和Dar，2004；Goulson等人，2005)。花粉含有蜜蜂的一系列重要的饮食氨基酸、脂肪、维生素和蛋白质，这些物质在不同物种之间存在差异(Roulston和Cane，2000)，但尤其是类固醇具有很高的种内变异(Villette等人，2015)，并且可以高度专一性地收集它们(Moerman等人，2017)。蜜蜂不能合成它们自己的类固醇，因此饮食来源必须满足它们的所有生理需求(Behmerand Nes，2003；Roulston和Cane，2000)。因此，花粉选择可能会受到这些要求的限制，这为不同物种的狭隘或灵活的觅食策略提供了一个潜在的解释。因此，分类群特定的营养需求以及植物分布和丰度的变化可能是驱动某些传粉者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，存在着重大的知识空白。我们不知道大多数蜜蜂物种对类固醇的需求，我们对花粉中发现的类固醇多样性的知识也严重缺乏。我的工作将通过为在英国发现的一种新的蜜蜂和植物物种生成类固醇图谱来解决这一缺陷，以回答以下问题：英国花粉类固醇资源的分布是否有助于解释蜜蜂多样性和丰度的模式？不同种类的熊蜂对类固醇的营养需求和觅食选择有何不同？推荐的以传粉者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？花粉专家蜜蜂物种是否在不同的花卉景观中显示出保守的类固醇选择？

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?