Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA.
Am Nat. 2012 Oct;180(4):450-63. doi: 10.1086/667584. Epub 2012 Aug 22.
Plant traits that mediate mutualistic interactions are widespread, yet few studies have linked their macroevolutionary patterns with the ecological interactions they mediate. Here we merged phylogenetic and experimental approaches to investigate the evolution of two common mutualistic plant traits, extrafloral nectaries (EFNs) and leaf domatia. By using the flowering plant clade Viburnum, we tested whether macroevolutionary patterns support adaptive hypotheses and conducted field surveys and manipulative experiments to examine whether ecological interactions are concordant with evolutionary predictions. Phylogenetic reconstructions suggested that EFN-bearing species are monophyletic, whereas the evolution of domatia correlated with leaf production strategy (deciduous or evergreen) and climate. Domatia were also more common in the EFN clade, suggesting that the two traits may jointly mediate ecological interactions. This result was further investigated in a common-garden survey, where plants with domatia and EFNs on the leaf blade had more mutualistic mites than plants with other trait combinations, and in manipulative field experiments, where the traits additively increased mutualist abundance. Taken together, our results suggest that mutualistic traits in Viburnum are not ecologically independent, as they work in concert to attract and retain mutualists, and their long-term evolution may be influenced by complex interactions among multiple traits, mutualists, and geography.
介导互利共生相互作用的植物特征广泛存在，但很少有研究将其宏观进化模式与其介导的生态相互作用联系起来。在这里，我们结合了系统发育和实验方法，研究了两种常见的互利共生植物特征——额外花蜜腺（EFN）和叶片气门的进化。我们使用开花植物科荚蒾属来检验宏观进化模式是否支持适应性假说，并进行了野外调查和操纵实验，以检验生态相互作用是否与进化预测一致。系统发育重建表明，具有 EFN 的物种是单系的，而气门的进化与叶片产生策略（落叶或常绿）和气候有关。气门在 EFN 分支中也更为常见，这表明这两个特征可能共同介导生态相互作用。这一结果在一个共同花园调查中得到了进一步研究，其中在叶片上具有气门和 EFN 的植物比具有其他特征组合的植物有更多的互利共生螨虫，并且在操纵性野外实验中，这些特征可累加增加互利共生生物的丰度。总的来说，我们的结果表明，荚蒾属中的互利共生特征在生态上并不是独立的，因为它们协同作用以吸引和保留互利共生生物，并且它们的长期进化可能受到多种特征、互利共生生物和地理因素之间复杂相互作用的影响。
