Data from: Breakdown of a geographic cline explains high performance of introduced populations of a weedy invader

1. What drives the evolution of increased growth and fecundity in plants introduced to a novel range is not well understood.

2. We investigate between-range differences in performance for Verbascum thapsus, a weedy invader known to grow larger in its introduced than native range. Specifically, we question whether adaptation to herbivory or climate best explains increased performance of introduced populations.

3. We grew 14 native and 22 introduced populations of V. thapsus in two common garden locations: near Prague, Czech Republic (native range) and in Colorado, USA (introduced range). By removing herbivores from half of the plants within each garden we tested the prediction of the Evolution of Increased Competitive Ability (EICA) hypothesis: increased performance is driven by an evolutionary shift of resources away from defence against herbivory towards growth and reproduction. We then investigated whether genetically based clines in performance are expressed along climate gradients within both the native and introduced ranges.

4. On average, seeds produce larger rosettes when collected from the introduced versus native range. While this evolution of increased growth in introduced populations in part matches the prediction of EICA, climate, not herbivory, best explains this between-range difference. Specifically, seeds collected from the native range produce smaller rosettes as the climate of origin becomes cooler and drier, while there is no cline in performance in rosettes grown from seed collected from the introduced range, which are large regardless of climate of origin. Thus, a climate-based cline within the native range best explains lower average performance of native compared to introduced populations.

SYNTHESIS: The breakdown in a potentially adaptive cline emphasizes the need to more closely investigate the evolutionary processes that shape geographic structuring (or its absence) within the introduced range. In addition, EICA is not universally applicable to all invasion scenarios, and our findings underscore the importance of testing underlying assumptions alongside the predictions of this hypothesis.

1. 人们对引种至新生境的植物其生长与繁殖力提升的演化驱动机制仍不甚明晰。
2. 本研究以广布性入侵杂草毛蕊花（Verbascum thapsus）为研究对象，该物种在引种分布范围相较于原生范围可生长得更为高大。我们旨在探究不同分布区间内该物种的表现差异，并试图明确：是对植食性生物的适应性演化，还是气候因素，更能解释引种种群表现提升的现象。
3. 我们在两个同质种植园地点开展栽培实验：一处位于捷克共和国布拉格附近（对应毛蕊花的原生分布范围），另一处位于美国科罗拉多州（对应其引种分布范围），共栽培14个原生种群与22个引种种群。通过移除每个种植园中半数植株上的植食者，我们对增强竞争能力演化（Evolution of Increased Competitive Ability, EICA）假说的预测进行了验证——该假说认为，植物表现提升源于资源的演化重分配：从抵御植食性生物转向生长与繁殖。随后，我们进一步探究了在原生与引种分布范围内，是否存在由遗传决定的表现性状沿气候梯度的渐变群（cline）表达。
4. 平均而言，从引种种群采集的种子所萌发的莲座株丛，相较于原生种群采集的种子更大。尽管引种种群生长提升的演化趋势部分契合EICA假说的预测，但真正能解释该分布区间差异的关键因素是气候，而非植食性压力。具体而言，原生种群采集的种子，其母本原产地气候越冷凉干燥，萌发的莲座株丛越小；而引种种群的莲座株丛表现并无此类渐变群特征，无论其母本原产地气候如何，株丛均保持较大体型。因此，原生分布范围内基于气候的渐变群，最能解释原生种群平均表现低于引种种群的现象。

SYNTHESIS: 综合分析：原本具有适应性的渐变群在引种范围内的消失，凸显了我们需要更深入地探究塑造引种分布区内地理结构（或无地理结构）的演化过程。此外，EICA假说并非适用于所有入侵场景，本研究结果也强调了在验证该假说预测的同时，对其核心假设进行检验的重要性。