Parallel selection on thermal physiology facilitates repeated adaptation of city lizards to urban heat islands.

Only recently have we begun to understand the ecological and evolutionary effects of urbanization on species, with studies revealing drastic impacts on community composition, gene flow, behaviour, morphology and physiology. However, our understanding of how adaptive evolution allows species to persist, and even thrive, in urban landscapes is still nascent. Here, we examine phenotypic, genomic and regulatory impacts of urbanization on a widespread lizard, the Puerto Rican crested anole (Anolis cristatellus). We find that urban lizards endure higher environmental temperatures and display greater heat tolerance than their forest counterparts. A single non-synonymous polymorphism within a protein synthesis gene (RARS) is associated with heat tolerance plasticity within urban heat islands and displays parallel signatures of selection in cities. Additionally, we identify groups of differentially expressed genes between habitats showing elevated genetic divergence in multiple urban-forest comparisons. These genes display evidence of adaptive regulatory evolution within cities and disproportionately cluster within regulatory modules associated with heat tolerance. This study provides evidence of temperature-mediated selection in urban heat islands with repeatable impacts on physiological evolution at multiple levels of biological hierarchy.