Key Laboratory for Plant Diversity and Biogeography of East Asia, Kunming Institute of Botany, Chinese Academy of Sciences, CN, 650201, Kunming, PR China.
Department of Biological Sciences, Macquarie University, Ryde, NSW, 2109, Australia.
Sci Rep. 2020 Feb 3;10(1):1660. doi: 10.1038/s41598-020-58102-7.
'Pollination syndromes' involving floral nectar have eluded satisfactory evolutionary explanation. For example, floral nectars for vertebrate-pollinated plants average low sugar concentrations, while such animals prefer high concentrations, perplexing pollination biologists and arousing recent controversy. Such relationships should result from evolutionary games, with plants and pollinators adopting Evolutionarily Stable Strategies, and nectar manipulating rather than attracting pollinators. Plant potential to manipulate pollinators depends on relationships between neighbouring flowers within plants, for all nectar attributes, but this has not been investigated. We measured nectar volume, concentration and sugar composition for open flowers on naturally-growing Blandfordia grandiflora plants, presenting classic bird-pollinated plant syndrome. To evaluate potential pollinator manipulation through nectar, we analysed relationships between neighbouring flowers for nectar volume, concentration, proportion sucrose, log(fructose/glucose), and sugar weight. To evaluate potential attraction of repeat-visits to flowers or plants through nectar, we compared attributes between successive days. Nearby flowers were positively correlated for all attributes, except log(fructose/glucose) as fructose≈glucose. Most relationships between nectar attributes for flowers and plants on successive days were non-significant. Nectar-feeding pollinators should therefore decide whether to visit another flower on a plant, based on all attributes of nectar just-obtained, enabling plants to manipulate pollinators through adjusting nectar. Plants are unlikely to attract repeat pollinator-visits through nectar production. Floral nectar evolution is conceptually straightforward but empirically challenging. A mutant plant deviating from the population in attributes of nectar-production per flower would manipulate, rather than attract, nectar-feeding pollinators, altering pollen transfer, hence reproduction. However, links between floral nectar and plant fitness present empirical difficulties.
涉及花卉花蜜的“传粉综合征”一直难以得到令人满意的进化解释。例如，脊椎动物传粉植物的花卉花蜜平均含糖量较低，而这些动物更喜欢高浓度的花蜜，这让传粉生物学家感到困惑，并引发了最近的争议。这种关系应该是由进化博弈产生的，植物和传粉者采用进化稳定策略，而花蜜则是操纵而不是吸引传粉者。植物操纵传粉者的能力取决于植物内相邻花朵之间的关系，适用于所有花蜜属性，但这尚未得到研究。我们测量了自然生长的 Blandfordia grandiflora 植物上开放花朵的花蜜量、浓度和糖组成，呈现出典型的鸟类传粉植物综合征。为了评估通过花蜜进行潜在传粉者操纵，我们分析了相邻花朵之间花蜜量、浓度、蔗糖比例、log(fructose/glucose)和糖重的关系。为了评估通过花蜜对花朵或植物的重复访问的潜在吸引力，我们比较了连续几天的属性。除了 log(fructose/glucose)（因为果糖≈葡萄糖）外，所有属性的相邻花朵均呈正相关。大多数连续几天花朵和植物之间的花蜜属性关系均无显著差异。因此，花蜜取食传粉者应该根据刚刚获得的花蜜的所有属性来决定是否访问植物上的另一朵花，从而使植物能够通过调整花蜜来操纵传粉者。植物不太可能通过花蜜的产生来吸引重复的传粉者访问。花卉花蜜的进化在概念上是简单的，但在经验上是具有挑战性的。与种群相比，每朵花的花蜜产量属性发生突变的植物会操纵而不是吸引花蜜取食传粉者，从而改变花粉传递，进而影响繁殖。然而，花卉花蜜与植物适应性之间的联系存在经验上的困难。
