Data from: Evidence for rapid evolutionary change in an invasive plant in response to biological control

We present evidence that populations of an invasive plant species that have become re-associated with a specialist herbivore in the exotic range through biological control have rapidly evolved increased anti-herbivore defences compared to populations not exposed to biocontrol. We grew half-sib families of the invasive plant Lythrum salicaria sourced from 17 populations near Ottawa, Canada, that differed in their history of exposure to a biocontrol agent, the specialist beetle Neogalerucella calmariensis. In a greenhouse experiment, we manipulated larval and adult herbivory to examine whether a population's history of biocontrol influenced plant defence and growth. Plants sourced from populations with a history of biocontrol suffered lower defoliation than naïve, previously unexposed populations, strongly suggesting they had evolved higher resistance. Plants from biocontrol-exposed populations were also larger and produced more branches in response to herbivory, regrew faster even in the absence of herbivory, and were better at compensating for the impacts of herbivory on growth (i.e., they exhibited increased tolerance). Furthermore, resistance and tolerance were positively correlated among genotypes with a history of biocontrol but not among naïve genotypes. Our findings suggest that biocontrol can rapidly select for increased defences in an invasive plant, and may favour a mixed defence strategy of resistance and tolerance without an obvious cost to plant vigour. While rarely studied, such evolutionary responses in the target species have important implications for the long-term efficacy of biocontrol programmes.

本研究提供证据表明，相较于未暴露于生物防治（biological control）的种群，通过生物防治手段在入侵分布区重新与专食性植食性昆虫（specialist herbivore）建立关联的入侵植物种群，已快速演化出更强的抗植食防御能力。我们以采集自加拿大渥太华附近17个种群的入侵植物千屈菜（Lythrum salicaria）的半同胞家系为实验材料，这些种群对作为生物防治因子（biocontrol agent）的专食性甲虫黑纹萤叶甲（Neogalerucella calmariensis）的暴露历史存在差异。在温室试验中，我们通过调控幼虫与成虫的植食为害强度，探究种群的生物防治暴露历史是否会影响植物的防御性状与生长表现。相较于未经历过生物防治的未暴露（naïve）种群，来自有生物防治暴露历史种群的植株，其落叶程度更低，这强烈表明它们已演化出更高的抗取食抗性（resistance）。来自暴露于生物防治种群的植株，在遭受植食为害时不仅体型更大、分枝更多，即使在无植食为害的情况下，其再生速度也更快，且更能补偿植食为害对生长造成的影响（即表现出更强的耐害性（tolerance））。此外，在具有生物防治暴露历史的基因型中，抗性与耐害性呈正相关，但在未暴露的基因型中则无此关联。我们的研究结果表明，生物防治可快速对入侵植物产生选择压，使其防御能力增强，且可能会青睐兼具抗性与耐害性的混合防御策略，且未对植株活力（plant vigour）产生明显的适合度成本。尽管针对靶标物种的此类演化响应研究鲜有报道，但这类响应对生物防治项目（biocontrol programmes）的长期有效性具有重要意义。