Escape from floral herbivory by early flowering in Arabidopsis halleri subsp. gemmifera

摘要

Natural selection on flowering phenology has been studied primarily in terms of plant-pollinator interactions and effects of abiotic conditions. Little is known, however, about geographic variation in other biotic factors such as herbivores and its consequence for differential selection on flowering phenology among populations. Here, we examine selection by floral herbivores on the flowering phenology of Arabidopsis halleri subsp. gemmifera using two adjacent populations with contrasting herbivory regimes. Intensive floral herbivory by the leaf beetle Phaedon brassicae occurs in one population, while the beetle is absent in another population. We tested the hypothesis that the two populations experience differential selection on flowering time that is attributable to the presence or absence of floral herbivory. A two-year field study showed that early flowering was favoured in the population under intensive floral herbivory, whereas selection for early flowering was not found in one year in the population where floral herbivory was absent. Selection for early flowering disappeared when the abundance of floral herbivores was artificially decreased in a field experiment. Thus, the heterogeneous distribution of P. brassicae was a major agent for differential selection on flowering time. However, flowering time did not differ between the two populations when plants were grown in the laboratory. The lack of genetic differentiation in flowering time may be explained by ongoing gene flow or recent invasion of P. brassicae. This study illustrates that the role of floral herbivory in shaping geographic variation in selection on flowering phenology may be more important than previously thought.展开▼

机译：对开花物候的自然选择主要是根据植物与传粉媒介的相互作用以及非生物条件的影响进行研究的。然而，人们对其他生物因子（例如草食动物）的地理变异及其对种群间开花物候的差异选择的后果知之甚少。在这里，我们根据拟南芥（Arabidopsis halleri）亚种的开花物候研究了由草食性动物选择。使用两个相邻种群的草食动物形成对比的双子植物。在一个种群中发生了叶甲虫密集的花食草，而在另一种群中则没有甲虫。我们检验了以下假设：这两个种群在开花时间上经历差异选择，这归因于是否存在花卉食草动物。一项为期两年的田野研究表明，在密集的花卉食草性种群中，较早开花的人群比较喜欢，而在没有花卉食草性的人群中，一年中没有选择早期开花。当在田间试验中人为减少花草食动物的丰度时，早花的选择消失了。因此，芸苔假单胞菌的异质分布是开花时间差异选择的主要因素。但是，当在实验室中种植植物时，两个种群之间的开花时间没有差异。开花期缺乏遗传分化的原因可能是持续的基因流动或近来的芸苔假单胞菌入侵。这项研究表明，花卉食草动物在选择开花物候时在塑造地理变异方面的作用可能比以前认为的更为重要。展开▼

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