Urbanization drives adaptation to cyanobacterial blooms in zooplankton grazers

Understanding how species and populations respond to urbanization is a crucial topic of contemporary evolutionary biology and has substantial practical relevance for biodiversity conservation. Eutrophication and subsequent cyanobacterial blooms due to rapid urbanization are reshaping aquatic ecosystems and altering biological evolution. In an integrated multivariate approach that addresses morphological and life history traits, we tested the hypotheses that zooplankton grazers inhabiting more urbanized waters had become more tolerant to urban cyanobacterial blooms through adaptive evolution. We also quantified the relative importance of phenotypic plasticity, evolution of mean trait values (constitutive evolution), and evolution of phenotypic plasticity to total trait changes under urbanization using a reaction norm approach. We found that urban grazers have genetically adapted to urban cyanobacterial bloom, which is due primarily to selection for reduced cyanobacteria-induced phenotypic plasticity in urban eutrophic conditions. The evolution of plasticity has been instrumental in driving alterations across multiple traits. Our experiment provides strong support for contemporary adaptive evolution under urbanization, and highlighted the importance of quantifying genetic variation in phenotypic plasticity when evaluating drivers and mechanism of population evolution in cities.