González-Varo Juan P, Ortiz-Sánchez F Javier, Vilà Montserrat
Conservation Science Group, Dept. Zoology, University of Cambridge, Cambridge, United Kingdom.
Department of Integrative Ecology, Estación Biológica de Doñana (EBD-CSIC), Sevilla, Spain.
PLoS One. 2016 Sep 22;11(9):e0163122. doi: 10.1371/journal.pone.0163122. eCollection 2016.
Extreme specialization is a common phenomenon in antagonistic biotic interactions but it is quite rare in mutualistic ones. Indeed, bee specialization on a single flower species (monolecty) is a questioned fact. Here, we provide multiple lines of evidence on true monolecty in a solitary bee (Flavipanurgus venustus, Andrenidae), which is consistent across space (18 sites in SW Iberian Peninsula) and time (three years) despite the presence of closely related congeneric plant species whose flowers are morphologically similar. The host flower (Cistus crispus, Cistaceae) is in turn a supergeneralist, visited by at least 85 insect species. We uncover ultraviolet light reflectance as a distinctive visual cue of the host flower, which can be a key mechanism because bee specialization has an innate basis to recognize specific signals. Moreover, we hypothesized that a total dependence on an ephemeral resource (i.e. one flower species) must lead to spatiotemporal matching with it. Accordingly, we prove that the bee's flight phenology is synchronized with the blooming period of the host flower, and that the densities of bee populations mirror the local densities of the host flower. This case supports the 'predictable plethora' hypothesis, that is, that host-specialization in bees is fostered by plant species providing predictably abundant floral resources. Our findings, along with available phylogenetic information on the genus Cistus, suggest the importance of historical processes and cognitive constraints as drivers of specialization in bee-plant interactions.
极端特化是拮抗生物相互作用中的常见现象，但在互利共生的相互作用中却相当罕见。事实上，蜜蜂对单一花种的特化（单食性）是一个存在争议的事实。在这里，我们提供了多条证据证明一种独居蜜蜂（黄斑短柄蜂，地蜂科）存在真正的单食性，尽管存在形态相似的近缘同属植物物种，但这种现象在空间上（伊比利亚半岛西南部的18个地点）和时间上（三年）都是一致的。其寄主花（岩蔷薇，半日花科）反而是一种超级泛化种，至少有85种昆虫会访花。我们发现紫外线反射是寄主花独特的视觉线索，这可能是一个关键机制，因为蜜蜂的特化有识别特定信号的先天基础。此外，我们推测完全依赖短暂资源（即一种花种）必然会导致与它在时空上的匹配。相应地，我们证明了蜜蜂的飞行物候与寄主花的花期同步，并且蜜蜂种群密度反映了当地寄主花的密度。这个案例支持了“可预测的丰富性”假说，即蜜蜂对寄主的特化是由提供可预测丰富花蜜资源的植物物种促成的。我们的发现，连同岩蔷薇属现有的系统发育信息，表明历史过程和认知限制作为蜜蜂与植物相互作用中特化驱动因素的重要性。
