Are sterols landscape limiting nutrients for wild bees in the UK?

甾醇是昆虫的必需营养素（例如，用于膜流动性、激素和生理功能）。植物营养组织中的甾醇主要包含两种甾醇; β-谷甾醇和豆甾醇。然而，在花粉中-蜜蜂从中获得营养供应-甾醇在结构上是多样化的，并且高度可变。我们的试验数据显示，在基尤全球收集的代表50多个家族的100多株植物中，25种花粉甾醇之间存在显著差异，其中特定甾醇组发生在密切相关的植物中。对蜜蜂-这方面唯一得到充分研究的蜂种-营养需求的研究表明，它们不能合成甾醇，其组织甾醇组成由其饮食中的特定甾醇决定。因此，就甾醇而言，蜜蜂是他们吃的东西。我们还从现有的人工饲料研究中了解到，蜜蜂幼虫的生长和存活对它们的膳食固醇高度敏感。例如，蜜蜂需要24-亚甲基胆固醇（24 MC）进行育雏，当饮食中补充这种固醇时，它们的发育显着改善。我们的试验数据显示，24 MC在为幼虫提供的皇家浆和蜜蜂流行的一系列植物花粉中含量丰富，在蔷薇科中，但在许多植物科中不存在，包括菊科，这是蜜蜂避免的花粉，表明甾醇组成可能影响蜜蜂的花粉选择。然而，关于野生蜜蜂物种的营养需求，特别是甾醇，几乎一无所知，但我们的试点工作表明，蜜蜂的甾醇谱在不同物种之间差异很大，但与这些蜜蜂收集的花粉的甾醇谱非常匹配。例如，常春藤花粉（Hedera helix）中的甾醇与常春藤蜜蜂（Colletes hederae）中的甾醇非常相似，后者专门在常春藤上觅食花粉。此外，虽然常春藤蜜蜂和常春藤花粉的甾醇匹配，但它们与大黄蜂的甾醇显著不同，大黄蜂的甾醇与它们收集的花粉匹配。这些又与红梅森蜜蜂（壁蜂）的甾醇不同。花粉和蜜蜂甾醇化学之间的这种密切联系强烈表明，这些其他蜜蜂使用它们收集的花粉中的特定甾醇。我们目前不知道这些差异是否反映了甾醇耐受性的差异或甾醇需求的差异。这个项目将首次测试这一点。无论哪种方式，这些差异都将为蜜蜂种群和群落动态提供机械基础，因此也是保护不同蜜蜂群落及其提供的生态系统服务的宝贵工具。我们将对英国植物花粉和英国野生蜜蜂中的甾醇营养素进行首次全面评估。利用这些数据，我们将确定能够支持野生蜜蜂物种最大多样性的关键植物物种。这些数据将被整合到花粉资源的景观尺度模型，以告知花粉甾醇在英国的供应。基于植物分布测量的景观规模建模将用于估计景观支持传粉者种群的能力，从现有的花蜜和碳水化合物评估向前迈出了一大步。我们将这些数据与野生蜜蜂物种的评估相匹配，以确定特定花粉甾醇对特定蜜蜂的重要性。我们将进行有史以来第一次评估甾醇如何影响野生蜜蜂的发育，以充分了解景观中甾醇限制的潜在成本，蜜蜂物种如何依赖特定的甾醇以及这如何影响野生蜜蜂的专业化。我们的数据将为英国政府的25年环境计划和国家传粉者战略以及更广泛的恢复花卉景观以支持蜜蜂的举措提供信息。

Sterols are essential nutrients for insects (e.g., for membrane fluidity, hormones and physiological functions). Sterols in plant vegetative tissues predominantly comprise two sterols; beta-sitosterol and stigmasterol. However, in pollen - from which bees obtain their nutrient provision - sterols are structurally diverse and highly variable. Our pilot data show striking variations among 25 pollen sterols across more than 100 plants representing over 50 families sampled from a global collection at Kew with specific sterol groups occurring in closely related plants. Research on the nutritional requirements of honey bees - the only well-studied bee species in this respect - indicates that they cannot synthesise sterols and that their tissue sterol composition is determined by the specific sterols in their diet. Thus, in terms of sterols bees are what they eat. We also know from existing research on artificial diets that honey bee larval growth and survival is highly sensitive to their dietary sterols. For example, honey bees require 24-methylenecholesterol (24MC) for brood rearing and their development is improved significantly when diets are supplemented with this sterol. Our pilot data shows that 24MC is abundant in royal jelly provisioned to larvae and in a range of plant pollens popular with honey bees e.g., in the Rosaceae but is absent from many plant families including Asteraceae which is avoided for pollen by honey bees suggesting sterol composition could influence pollen choice in bees. However, almost nothing is known about the nutritional needs of wild bee species, especially sterols, but our pilot work shows that the sterol profiles of bees vary dramatically across different species but closely match the sterol profiles of the pollen collected by these bees for food. For example, the sterols from ivy flower pollen (Hedera helix) are highly similar to those of the ivy bee (Colletes hederae), which forages exclusively on ivy for pollen. Furthermore, while the sterols of ivy bees and ivy pollen match they differ dramatically from sterols of bumble bees which have sterols matching the pollen they collect. These in turn differ from the sterols of red mason bees (Osmia bicornis). This close association between pollen and bee sterol chemistry strongly suggests that these other bees use the specific sterols in the pollen they collect. We do not currently know whether these differences reflect differences in sterol tolerances or differences in sterol requirements. This project will test this for the first time. Either way, these differences would provide a mechanistic basis for bee population and community dynamics, and thus also a valuable tool in conserving diverse bee communities and the ecosystem services they provide. We will undertake the first comprehensive assessment of sterol nutrients in pollen of UK plants and in UK wild bees. Using these data, we will identify key plant species that can support the greatest diversity of wild bee species. These data will be integrated into landscape scale models of pollen resources to inform pollen sterol provision in the UK. Landscape-scale modelling based on measurements of plant distributions will be used to estimate the capacity of the landscape to support pollinator populations, taking a major step forward from existing assessments on nectar and carbohydrates. We will match these data with assessments of wild bee species to determine how important specific pollen sterols are for specific bees. We will conduct the first ever assessment of how sterols influence development in wild bees to understand fully the potential cost of sterol limitations in the landscape, how dependent bee species are on specific sterols and how this influences specialisation in wild bees. Our data will inform delivery of the UK government's 25 Year Environment Plan and National Pollinator Strategy and wider initiatives to renew floral landscapes in support of bees.