Research output

The heat is on: Genetic adaptation to urbanization mediated by thermal tolerance and body size

Research output: Contribution to journalA1: Web of Science-article


  • Kristien I Brans
  • Mieke Jansen
  • Nedim Tüzün
  • Robby Stoks
  • Luc De Meester

Departments, research groups and services

External Organisations

  • Laboratory of Aquatic Ecology, Evolution and Conservation, KU Leuven, Leuven, Belgium.


Original languageEnglish
JournalGlobal Change Biology
Issue number12
Pages (from-to)5218-5227
Number of pages10
Publication statusPublished - Dec-2017


Worldwide, urbanization leads to tremendous anthropogenic environmental alterations, causing strong selection pressures on populations of animals and plants. Although a key feature of urban areas is their higher temperature ("urban heat islands"), adaptive thermal evolution in organisms inhabiting urban areas has rarely been studied. We tested for evolution of a higher heat tolerance (CTMAX ) in urban populations of the water flea Daphnia magna, a keystone grazer in freshwater ecosystems, by carrying out a common garden experiment at two temperatures (20°C and 24°C) with genotypes of 13 natural populations ordered along a well-defined urbanization gradient. We also assessed body size and haemoglobin concentration to identify underlying physiological drivers of responses in CTMAX . We found a higher CTMAX in animals isolated from urban compared to rural habitats and in animals reared at higher temperatures. We also observed substantial genetic variation in thermal tolerance within populations. Overall, smaller animals were more heat tolerant. While urban animals mature at smaller size, the effect of urbanization on thermal tolerance is only in part caused by reductions in body size. Although urban Daphnia contained higher concentrations of haemoglobin, this did not contribute to their higher CTMAX . Our results provide evidence of adaptive thermal evolution to urbanization in the water flea Daphnia. In addition, our results show both evolutionary potential and adaptive plasticity in rural as well as urban Daphnia populations, facilitating responses to warming. Given the important ecological role of Daphnia in ponds and lakes, these adaptive responses likely impact food web dynamics, top-down control of algae, water quality, and the socio-economic value of urban ponds.

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  • Brans_et_al-2017-Global_Change_Biology

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