Data from: Invasive success and the evolution of enhanced weaponry

A key hypothesis that has been proposed to explain plants’ invasive success suggests that some invasive species produce allelochemicals that are novel against naïve neighbours at the introduced range and therefore provide an advantage there (novel weapons hypothesis – NWH). However, a seldom-studied hypothesis suggests that invasive populations could not only possess novel weapons, but might also evolve their enhanced production. Moreover, so far no study has examined both the novelty and evolution of allelopathic effects. Here, we examined these two hypotheses in a set of experiments with the highly invasive plant Impatiens glandulifera. In the first experiment, we examined the evolution of allelopathic ability by comparing the inhibitory effects of leaf extracts from native versus invasive I. glandulifera on the germination success of its dominant neighbour Urtica dioica. In the following experiments, we examined the NWH by comparing the germination success of U. dioica seeds collected at the native versus invasive range of I. glandulifera, in response to either leaf extracts or soil trained with invasive I. glandulifera. The results of the first experiment indicate that invasive I. glandulifera exert a stronger inhibitory effect on the germination of U. dioica compared to their native counterparts, providing support for the hypothesis that allelopathic ability can evolve at the invasive range. However, the results of the two following experiments reveal no difference in the response of U. dioica from the native versus invasive range of I. glandulifera, to the allelopathic effects of either the leaf extracts or the trained soil. These results therefore do not provide support for the NWH, and suggest that increased allelopathy in invasive I. glandulifera might have been selected for by other processes. The results of this study call for biogeographical experiments that will examine not only the novelty but also the evolution of allelopathic effects in invasive plants.为阐释植物的入侵成功机制，学界曾提出一项核心假说：部分入侵物种可产生化感物质（allelochemicals），这类物质对其入侵分布区内未接触过该类物质的邻株具有新颖性，进而能为入侵物种带来竞争优势，即新武器假说（novel weapons hypothesis – NWH）。然而，另有一项鲜有研究的假说指出，入侵种群不仅可携带这类新颖化感物质，还可能演化出更强的化感物质合成能力。此外，迄今为止尚无研究同时考察化感效应（allelopathic effects）的新颖性与演化特性。 本研究以恶性入侵植物凤仙花（Impatiens glandulifera）为研究材料，通过一系列实验对上述两项假说进行验证。第一组实验中，我们通过对比本土种群与入侵种群凤仙花的叶片提取物对其优势邻株荨麻（Urtica dioica）萌发成功率的抑制效应，考察化感能力的演化过程。后续实验中，我们则通过对比采集自凤仙花本土分布区与入侵分布区的荨麻种子，在分别经入侵种群凤仙花叶片提取物或定植土壤处理后的萌发成功率，验证新武器假说。 第一组实验结果显示，相较于本土种群，入侵种群凤仙花对荨麻萌发的抑制效应更强，这为“化感能力可在入侵分布区内发生演化”的假说提供了支持。但后续两组实验的结果表明，无论面对叶片提取物还是定植土壤的化感效应，采集自凤仙花本土分布区与入侵分布区的荨麻种子的响应均无显著差异。因此本研究结果并不支持新武器假说，并提示入侵种群凤仙花的化感作用增强，可能是由其他演化过程所选择塑造的。 本研究的结果呼吁开展生物地理学实验，以同时考察入侵植物化感效应的新颖性与演化特性。