Data from: City life on fast lanes: urbanization induces an evolutionary shift towards a faster life style in the water flea Daphnia

Multiple species show significant trait shifts in response to urbanization. Yet, the impact of anthropogenic warming linked to the urban heat island effect is remarkably understudied. Additionally the relative contributions of phenotypic plasticity and genetic change underlying trait shifts in response to urbanization are poorly known. A common garden study with the water flea Daphnia magna revealed that both genetic differentiation in response to urbanization and phenotypic plasticity in response to higher rearing temperature (24 °C) induced significant parallel multivariate shifts in life history strategy along the slow-fast pace-of-life axis. Urban animals and animals reared at higher temperatures are characterized by fast maturation, early release of progeny, a smaller size at maturity, increased fecundity, and higher performance (given by maximal population growth rate r) compared to genotypes isolated from rural ponds and animals reared at lower temperatures respectively. Evolution in response to urbanization accounted for 30% of the total observed shift in life history and caused a significant change in mean trait values, while plasticity responses to experimental warming were unaltered between urban and rural populations. The total trait change achieved through both plasticity and evolution ranged from 8 to 56% depending on the trait. Our results provide clear evidence for evolution underlying an increase in pace-of-life of populations in response to urbanization. Given the pivotal role of Daphnia in aquatic ecosystems, this shift potentially feeds back to population structure, top-down control of algae, and food web dynamics in urban freshwater ecosystems. Additionally, we argue that adaptation to urban heat islands might render these populations pre-adapted in a context of future climate change.

诸多物种会因城市化进程发生显著的性状偏移。然而，与城市热岛效应（urban heat island effect）相关的人为变暖所产生的影响，迄今仍未得到充分研究。此外，城市化驱动的性状偏移背后，表型可塑性（phenotypic plasticity）与遗传分化的相对贡献也鲜为人知。本研究以大型溞（Daphnia magna）为对象开展同质园实验（common garden study），结果显示：针对城市化的遗传分化，以及针对饲养高温（24 ℃）的表型可塑性，二者均可沿快慢生活史轴（slow-fast pace-of-life axis），对生活史策略产生显著的平行多变量偏移。相较于从乡村池塘分离得到的基因型，以及在较低温度下饲养的个体而言，城市种群个体与高温饲养个体均具备以下特征：成熟速率更快、后代产出更早、成熟体型更小、繁殖力更高，且以种群最大增长率（r）表征的生存性能更强。城市化驱动的适应性演化可解释生活史总偏移量的30%，并使性状均值发生显著改变；而城乡种群对实验性增温的可塑性响应并无差异。结合可塑性与演化共同作用带来的总性状变化幅度，因性状不同介于8%至56%之间。本研究结果清晰证明：种群为响应城市化而产生的生活史节奏加快，其背后存在适应性演化的驱动作用。鉴于大型溞在水生生态系统中的核心地位，这类性状偏移可能会对城市淡水生态系统的种群结构、藻类下行调控以及食物网动态产生反馈影响。此外，本研究认为，对城市热岛效应的适应性演化，可使这些种群在未来气候变化的背景下具备预适应性。