Institute of Biology, University of Neuchâtel, Rue Emile-Argand 11, 2000, Neuchâtel, Switzerland.
INRAE, UMR Laboratoire d'Agronomie et Environnement, Vandoeuvre-lès, 54518, Nancy, France.
Sci Rep. 2020 Feb 7;10(1):2074. doi: 10.1038/s41598-020-59068-2.
One major goal in plant evolutionary ecology is to address how and why tritrophic interactions mediated by phytochemical plant defences vary across species, space, and time. In this study, we tested three classical hypotheses about plant defences: (i) the resource-availability hypothesis, (ii) the altitudinal/elevational gradient hypothesis and (iii) the defence escalation hypothesis. For this purpose, predatory soil nematodes were challenged to hunt for root herbivores based on volatile cues from damaged or intact roots of 18 Alpine Festuca grass species adapted to distinct climatic niches spanning 2000 meters of elevation. We found that adaptation into harsh, nutrient-limited alpine environments coincided with the production of specific blends of volatiles, highly attractive for nematodes. We also found that recently-diverged taxa exposed to herbivores released higher amounts of volatiles than ancestrally-diverged species. Therefore, our model provides evidence that belowground indirect plant defences associated with tritrophic interactions have evolved under two classical hypotheses in plant ecology. While phylogenetic drivers of volatile emissions point to the defence-escalation hypothesis, plant local adaptation of indirect defences is in line with the resource availability hypothesis.
植物进化生态学的主要目标之一是解决由植物化学生物防御介导的三营养级相互作用如何以及为何在物种、空间和时间上发生变化。在这项研究中，我们检验了关于植物防御的三个经典假设：（i）资源可用性假设，（ii）海拔梯度假设，以及（iii）防御升级假设。为此，我们利用受损或完整的根发出的挥发性气味来挑战捕食性土壤线虫，这些根来自适应 2000 米海拔跨度的不同气候小生境的 18 种高山羊茅草物种。我们发现，适应恶劣、营养有限的高山环境与产生特定挥发性混合物有关，这些混合物对线虫极具吸引力。我们还发现，与祖先分化的物种相比，最近分化的类群在暴露于食草动物时释放出更多的挥发性物质。因此，我们的模型提供了证据，表明与三营养级相互作用相关的地下间接植物防御是在植物生态学中的两个经典假设下进化而来的。虽然挥发性排放的系统发育驱动因素指向防御升级假设，但间接防御的植物局部适应与资源可用性假设一致。
