Department of Biology, Syracuse University, Syracuse, NY, 13244, USA,
Oecologia. 2013 Dec;173(4):1345-54. doi: 10.1007/s00442-013-2694-8. Epub 2013 Jul 9.
Florivores are present in many pollination systems and can have direct and indirect effects on both plants and pollinators. Although the impact of florivores are commonly examined in facultative pollination mutualisms, their effects on obligate mutualism remain relatively unstudied. Here, we used experimental manipulations and surveys of naturally occurring plants to assess the effect of florivory on the obligate pollination mutualism between yuccas and yucca moths. Yucca filamentosa (Agavaceae) is pollinated by the moth Tegeticula cassandra (Lepidoptera: Prodoxidae), and the mutualism also attracts two florivores: a generalist, the leaf-footed bug Leptoglossus phyllopus (Hemiptera: Coreidae), and a specialist, the beetle Hymenorus densus (Coleoptera: Tenebrionidae). Experimental manipulations of leaf-footed bug densities on side branches of Y. filamentosa inflorescences demonstrated that feeding causes floral abscission but does not reduce pollen or seed production in the remaining flowers. Similar to the leaf-footed bugs, experimental manipulations of beetle densities within individual flowers demonstrated that beetle feeding also causes floral abscission, but, in addition, the beetles also cause a significant reduction in pollen availability. Path analyses of phenotypic selection based on surveys of naturally occurring plants revealed temporal variation in the plant traits important to plant fitness and the effects of the florivores on fitness. Leaf-footed bugs negatively impacted fitness when fewer plants were flowering and leaf-footed bug density was high, whereas beetles had a positive effect on fitness when there were many plants flowering and their densities were low. This positive effect was likely due to adult beetles consuming yucca moth eggs while having a negligible effect on floral abscission. Together, the actions of both florivores either augmented the relationship of plant traits and fitness or slightly weakened the relationship. Overall, the results suggest that, although florivores are always present during flowering, the impact of florivores on phenotypic selection in yuccas is strongly mitigated by changes in their densities on plants from year to year. In contrast, both florivores consistently influenced pollinator larval mortality through floral abscission, and H. densus beetles additionally via the consumption of pollinator eggs.
食花动物存在于许多传粉系统中，对植物和传粉者都有直接和间接的影响。虽然在兼性传粉共生关系中经常研究食花动物的影响，但对专性共生关系的影响仍相对研究较少。在这里，我们使用实验操作和对自然发生的植物的调查来评估食花对丝兰和丝兰蛾之间专性传粉共生关系的影响。丝兰（龙舌兰科）由蛾类 Tegeticula cassandra（鳞翅目：Prodoxtidae）授粉，这种共生关系还吸引了两种食花动物：一种是叶足盲蝽 Leptoglossus phyllopus（半翅目：Coreidae），一种是专食性甲虫 Hymenorus densus（鞘翅目：Tenebrionidae）。在丝兰花序侧枝上对叶足盲蝽密度的实验操作表明，取食会导致花脱落，但不会减少剩余花中的花粉或种子产量。与叶足盲蝽类似，在单个花内对甲虫密度的实验操作表明，甲虫取食也会导致花脱落，但此外，甲虫还会导致花粉可用性显著减少。基于对自然发生植物的调查的表型选择的路径分析揭示了对植物适应性重要的植物性状的时间变化以及食花动物对适应性的影响。当开花植物较少且叶足盲蝽密度较高时，叶足盲蝽对适应性有负面影响，而当有许多植物开花且它们的密度较低时，甲虫对适应性有积极影响。这种积极影响可能是由于成年甲虫在消耗丝兰蛾卵的同时对花脱落的影响微不足道。总的来说，这两种食花动物的行为要么增强了植物性状和适应性之间的关系，要么略微削弱了这种关系。总体而言，研究结果表明，尽管食花动物在开花期总是存在，但它们对丝兰表型选择的影响因植物密度的逐年变化而得到极大缓解。相比之下，食花动物通过花脱落一致地影响传粉者幼虫的死亡率，并且 H. densus 甲虫还通过消耗传粉者卵来影响。
