Feeding the enemy: loss of nectar and nectaries to herbivores reduces tepal damage and increases pollinator attraction in Iris bulleyana

Floral nectar usually functions as a pollinator reward, yet it may also attract herbivores. However, the effects of herbivore consumption of nectar or nectaries on pollination have rarely been tested. We investigated Iris bulleyana, an alpine plant that has showy tepals and abundant nectar, in the Hengduan Mountains of SW China. In this region, flowers are visited mainly by pollen-collecting pollinators and nectarivorous herbivores. We tested the hypothesis that, in I. bulleyana, sacrificing nectar and nectaries to herbivores protects tepals and thus enhances pollinator attraction. We compared rates of pollination and herbivory on different floral tissues in plants with flowers protected from nectar and nectary consumption with rates in unprotected control plants. We found that nectar and nectaries suffered more herbivore damage than did tepals in natural conditions. However, the amount of tepal damage was significantly greater in the flowers with protected nectaries than in the control...花蜜通常作为传粉者的奖励报酬，但同时也可能吸引植食性动物。然而，植食动物取食花蜜或蜜腺（nectaries）对传粉过程的影响，迄今鲜有研究得到验证。我们在中国西南横断山脉（Hengduan Mountains）区域，针对兼具艳丽花被片（tepals）与丰富花蜜的高山植物云南鸢尾（Iris bulleyana）开展了相关研究。该区域内，该植物的花主要有两类访花类群：一类是采集花粉的传粉者，另一类是取食花蜜的植食性动物。我们提出如下研究假说：在云南鸢尾中，若植株将花蜜与蜜腺暴露给植食动物取食，可使花被片免受损害，进而增强对传粉者的吸引效果。为此我们设置了两组处理：一组为花朵的花蜜与蜜腺取食被阻断的植株，另一组为未做任何保护的对照植株，随后比较了两组植株不同花组织的传粉效率与植食损伤率。我们发现，自然条件下花蜜与蜜腺的植食损伤程度显著高于花被片；但在蜜腺被保护的花朵中，花被片的损伤量却显著高于对照植株……