The Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA, 02131, USA.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, 02138, USA.
Am J Bot. 2020 Feb;107(2):209-218. doi: 10.1002/ajb2.1434. Epub 2020 Feb 20.
Understanding how environmental stress affects the strength of mutualisms is critically important given observed and projected environmental changes. In particular, the frequency and duration of drought have been increasing worldwide. We investigated how water availability affects plant traits that mediate a pollination mutualism.
For butterfly-pollinated Phlox drummondii, we determined how moisture availability affects flower size, nectar volume, and nectar sugar amount. Furthermore, we explored the role that local adaptation may play in responses to moisture availability by including plants collected from regions that differ in aridity. Finally, we determined whether responses of plant populations to selection may differ under drought by calculating heritability of traits under control and dry conditions.
Flower size was generally smaller in dry plants than in control plants. Early in the treatment period, nectar volume and sugar were higher in dry plants than in control plants for plants from both arid and wetter regions. With prolonged dry treatment, nectar volume and sugar remained higher only in plants from the arid region. Heritability of floral traits was lower for water-limited plants than for control plants.
Plant investment into pollination mutualisms under environmental stress may depend on the extent to which populations are already locally adapted to such conditions, suggesting that mutualism may remain strong, at least in arid regions. However, decreases in heritability under water-limitation suggest that responses to selection imposed by pollinators may be low, even if drought-adapted plants maintain production of rewards to pollinators.
鉴于观察到的和预测到的环境变化，了解环境压力如何影响共生关系的强度至关重要。特别是，干旱的频率和持续时间在全球范围内一直在增加。我们研究了水分供应如何影响介导传粉共生的植物特征。
对于蝴蝶授粉的 Phlox drummondii，我们确定了水分供应如何影响花的大小、花蜜量和花蜜含糖量。此外，我们通过包括来自干旱程度不同地区的植物，探讨了本地适应可能在对水分供应的反应中所起的作用。最后，我们通过计算控制和干旱条件下性状的遗传力，确定植物种群对选择的反应是否会因干旱而有所不同。
与对照植株相比，干旱植株的花通常较小。在处理期的早期，来自干旱和湿润地区的植物的花蜜量和含糖量在干旱植株中均高于对照植株。随着干旱处理时间的延长，只有来自干旱地区的植物的花蜜量和含糖量仍保持较高水平。受水分限制的植物的花性状遗传力低于对照植物。
植物在环境压力下对传粉共生的投资可能取决于种群对这些条件的本地适应程度，这表明共生关系至少在干旱地区可能仍然很强。然而，在水分限制下遗传力的降低表明，即使适应干旱的植物仍能为传粉者提供报酬，对传粉者施加的选择反应也可能较低。
