Adaptive Evolution in Cities: Progress and Misconceptions

• Published in: Trends in ecology & evolution (Amsterdam) 2021-03, Vol.36 (3), p.239-257
• Main Authors: Lambert, Max R., Brans, Kristien I., Des Roches, Simone, Donihue, Colin M., Diamond, Sarah E.
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Biodiversity; Biological Evolution; Cities; convergent evolution; Ecosystem; local adaptation; maladaptation; parallel evolution; urban adapter; urban evolution; Urbanization
• ISSN: 0169-5347; 1872-8383
• DOI: 10.1016/j.tree.2020.11.002

Current narratives suggest that urban adaptation – the adaptive evolution of organisms to cities – is pervasive across taxa and cities. However, in reviewing hundreds of studies, we find only six comprehensive examples of species adaptively evolving to urbanization. We discuss the utility and shortcomings of methods for studying urban adaptation. We then review diverse systems offering preliminary evidence for urban adaptation and outline a research program for advancing its study. Urban environments constitute diverse, interacting selective agents that test the limits of adaptation. Understanding urban adaptation therefore offers unique opportunities for addressing fundamental questions in evolutionary biology and for better conserving biodiversity in cities. However, capitalizing on these opportunities requires appropriate research methods and dissemination of accurate narratives. There has been a recent, explosive interest in studying adaptive evolution in cities. However, many responses to urbanization may be misattributed as adaptation because sufficient evidence is lacking.We identified only six systems that offer strong evidence for urban–nonurban divergence that is both genetically based and adaptive.Common issues for inferring urban adaptation include assessing phenotypic or genetic divergence as the only criterion, using inappropriate developmental stages, and inadequately assessing fitness.More robust tests of adaptive urban evolution, particularly employing adequate experimental approaches and in more diverse taxa and locations, are urgently needed.Appropriately attributing adaptive urban evolution will maximize the use of cities in exploring fundamental evolutionary, ecological, and eco-evolutionary hypotheses.