Some like it hot: adaptation to the urban heat island in common dandelion.

The Urban Heat Island Effect (UHIE) is a globally consistent pressure on biological species living in cities. Rapid adaptation to the UHIE may be necessary for urban wild flora to persist in cities, but experimental evidence is scarce. Here, we report evidence of adaptive evolution in a perennial plant species in response to the UHIE. We collected seeds from common dandelion (<i>Taraxacum officinale</i>) individuals along an urban-rural gradient in the city of Amsterdam (The Netherlands). In common-environment greenhouse experiments, we assessed the effect of elevated temperatures on plant growth and the effect of vernalisation treatments on flowering phenology. We found that urban plants accumulate more biomass at higher temperatures and require shorter vernalisation periods, corresponding to milder winters, to induce flowering compared to rural plants. Differentiation was also observed between different intra-urban subhabitats, with park plants displaying a higher vernalisation requirement than street plants. Our results show genetic differentiation between urban and rural dandelions in temperature-dependent growth and phenology, consistent with adaptive divergence in response to the UHIE. Rapid adaptation to the UHIE may be a potential explanation for the persistence of dandelions in urban environments.

城市热岛效应（Urban Heat Island Effect, UHIE）是全球范围内持续作用于城市中生物类群的环境压力。城市野生植物若要在城市生境中存续，往往需要快速适应城市热岛效应，但相关实验证据仍较为匮乏。本研究报道了多年生植物物种响应城市热岛效应的适应性进化证据：我们从荷兰阿姆斯特丹市的城乡梯度上，采集了普通蒲公英（*Taraxacum officinale*）个体的种子。在统一环境的温室实验中，我们分别评估了升温对植物生长的影响，以及春化处理对开花物候的调控效应。结果显示，与乡村种群相比，城市种群在更高温度下可积累更多生物量，且诱导开花所需的春化时长更短——这与城市中更为温和的冬季气候特征相契合。此外，城市内部不同亚生境间也存在遗传分化：公园生境的蒲公英种群对春化的需求显著高于街道生境种群。本研究结果表明，城乡蒲公英在温度依赖型生长与开花物候方面存在遗传分化，这与城市热岛效应驱动的适应性分化模式一致。对城市热岛效应的快速适应，或可解释蒲公英为何能在城市环境中得以存续。