Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, K1N 6N5, Canada.
Rocky Mountain Biological Laboratory, Crested Butte, CO, 81224, USA.
Oecologia. 2021 Mar;195(3):559-574. doi: 10.1007/s00442-020-04786-7. Epub 2020 Oct 26.
Many bee species are dietary specialists and restrict their pollen foraging to a subset of the available flowers. However, the reasons for specialization-and the reasons certain plant taxa support numerous specialists-are often unclear. Many bees specialize on the plant family Asteraceae, despite evidence its pollen is a poor food for non-specialists. Here, we studied six mason bee (Osmia) species, including three Asteraceae specialists, to test whether observed pollen-usage patterns reflect larval nutritional requirements, to investigate what aspects of Asteraceae pollen make it unsuitable for non-specialists, and to understand how Asteraceae specialists tolerate their seemingly low-quality diet. We reared larval bees on host and nonhost pollen and found that Asteraceae specialists could develop on nonhost provisions, but that other bees could not survive on Asteraceae provisions. These effects did not seem related to nutritional deficiencies, since Asteraceae provisions were not amino acid deficient, and we found no consistent differences in digestive efficiency among pollen types. However, Asteraceae specialists completed more foraging flights per larva, generally collected relatively larger provisions, and produced more frass (waste) than the other species, suggesting quantitative compensation for low food quality. Toxins, deficiencies in unmeasured nutrients, or aspects of pollen grain structure might explain poor survival of non-specialists on Asteraceae provisions. Our results suggest that floral host selection by specialist bees is not related to optimizing larval nutrition. We recommend further investigation of host-selection behaviour in adult bees and of pollen digestion in larvae to better understand the evolution of bee-flower associations.
许多蜜蜂物种是专门觅食花粉的专家，它们只在有限的花中觅食。然而，专业化的原因以及某些植物类群支持众多专家的原因通常并不清楚。尽管有证据表明，花粉对非专家来说是一种不良食物，但许多蜜蜂仍专门以菊科植物为食。在这里，我们研究了六种壁蜂（Osmia）物种，包括三种菊科植物专家，以测试观察到的花粉使用模式是否反映了幼虫的营养需求，研究菊科花粉的哪些方面使其不适合非专家，以及了解菊科植物专家如何耐受它们看似低质量的饮食。我们用宿主和非宿主花粉饲养幼虫，并发现菊科植物专家可以在非宿主食物上发育，但其他蜜蜂不能在菊科植物食物上生存。这些影响似乎与营养缺乏无关，因为菊科花粉并不缺乏氨基酸，我们也没有发现不同花粉类型之间消化效率的一致差异。然而，菊科植物专家每只幼虫完成的觅食飞行次数更多，通常采集相对较大的食物，并产生更多的粪便（废物），这表明它们通过定量补偿来弥补低质量食物的影响。毒素、未测量营养素的缺乏，或花粉粒结构的某些方面可能解释了非专家在菊科花粉食物上的低存活率。我们的研究结果表明，专家蜜蜂对花的宿主选择与优化幼虫营养无关。我们建议进一步研究成年蜜蜂的宿主选择行为和幼虫的花粉消化，以更好地了解蜜蜂与花的进化关系。
