Fine-tuned floral filters in melittophilous flowers sort out particular bees

蜜蜂被认为是可靠的传粉者；蜜蜂访花的频率和花朵的恒定性证实了这一点，但蜜蜂为幼虫提供食物而收集花粉的做法对此提出了挑战。已经进入花粉运输结构的花粉粒不再可用于授粉。这种将花粉分配给授粉以外的目的对蜜蜂授粉的开花植物来说是一个两难境地。在这个项目中，我们将通过测试花是否以及如何操纵蜜蜂来优化花粉转移，来研究这一花粉困境的三个迄今未被研究和一致的方面。1.花粉粒的刺参与了防止蜂群采集花粉粒的机械防御。我们将测试刺数、刺长度、花粉粒直径、花粉水合作用和添加反流花蜜的作用，以了解刺状花粉抵御丛生蜜蜂采集的机制。此外，我们将测试开花植物是否使用带刺的花粉颗粒来限制蜜蜂收集花蜜，因为收集花蜜的蜜蜂不太频繁地梳理自己。2.在蜜蜂体内的安全位置上的花粉粒被梳理到花粉运输结构中的可能性较小，从那里它们不能授粉。我们将测试龙骨开花是否代表例外，是否可以将望远镜用作授粉蜜蜂的一种安全地点。我们将测试只有巨型蜜蜂才能打开的龙骨花的硬度是否代表着花的适应，以促进花粉粒从蜜蜂的腹侧望远镜转移到花的柱头上。这将是通过可育的本地花粉授粉的第一个证据，并对各自的花构成强大的选择压力，以排除没有腹侧望远镜的蜜蜂。3.许多蜜蜂授粉的花具有类似花粉和雄蕊的结构，这些结构被认为具有视觉导花的功能。我们将研究模拟花粉和雄蕊的结构通过触觉刺激触发蜜蜂梳理行为的功能，这一功能尚未被探索。我们将检验这样一种假设，即模拟雄蕊的结构比真正的雄蕊更容易被修饰。此外，我们还将测试在异花药花中，喂食雄蕊是否比授粉雄蕊更能诱导梳理。这些实验将表明，花是否能够通过触觉提示来操纵蜜蜂的梳理，以促进花粉向同种花的转移。这些研究的一致性方面是微调的花过滤器，通过它，蜜蜂授粉的花可能能够排除不同的蜜蜂，从而提高授粉成功。这些研究将集中在目前未被充分研究的访花蜜蜂和开花植物之间互惠互利的对抗性方面。

Bees are considered reliable pollinators; this is corroborated by the bees frequency of flower visits and their flower constancy, but challenged by the bees collection of pollen for larval food provisioning. Pollen grains which have been groomed into the pollen transport structures are no longer available for pollination. This allocation of pollen for a purpose other than pollination amounts to a dilemma for bee-pollinated flowering plants. In this project we will investigate three so far unstudied and coherent aspects of this pollen dilemma by testing whether and how flowers manipulate bees for optimization of pollen transfer. 1. Spines of pollen grains are involved in the mechanical defence of pollen grains from being collected by corbiculate bees. We will test the role of spine number, spine length, pollen grain diameter, pollen hydration and added regurgitated nectar in order to understand the mechanism by which spiny pollen is defended against collection by corbiculate bees. In addition we will test if flowering plants use spiny pollen grains to restrict bees to nectar collection, because nectar collecting bees groom themselves less frequently. 2. Pollen grains on safe sites of bees bodies experience a smaller probability of being groomed into the pollen transport structures, from where they cannot pollinate flowers. We will test whether keel blossoms represent an exception and can use the scopa as a kind of safe site of pollinating bees. We will test whether the stiffness of keel flowers, which can only be opened by megachilid bees, represents a floral adaptation to promote transfer of pollen grains from the ventral scopa of the bee to stigma of the flower. This would be the first evidence for pollination by fertile scopal pollen and constitute strong selective pressure for the respective flowers to exclude bees that do not possess a ventral scopa. 3. Many bee-pollinated flowers possess pollen- and stamen-mimicking structures which are considered to function as visual floral guides. We will study the as yet unexplored function of pollen- and stamen-mimicking structures to trigger grooming behaviour in bees by means of tactile stimuli. We will test the hypothesis that stamen-mimicking structures set a stronger trigger for grooming than real stamens. In addition we will test if feeding stamens induce grooming more strongly than pollination stamens in heterantherous flowers. These experiments will show if flowers are able to manipulate the bees grooming by tactile cues in order to promote pollen transfer to conspecific flowers. The coherent aspect of these studies is the fine-tuned floral filter by which bee-pollinated flowers might be able to exclude distinct bees and thereby improve pollination success. These studies will focus on currently understudied antagonistic aspects of the mutualism between flower-visiting bees and melittophilous flowering plants.