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The heat is on: Genetic adaptation to urbanization mediated by thermal tolerance and body size
Author(s) -
Brans Kristien I.,
Jansen Mieke,
Vanoverbeke Joost,
Tüzün Nedim,
Stoks Robby,
De Meester Luc
Publication year - 2017
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.13784
Subject(s) - daphnia , biology , urbanization , ecology , critical thermal maximum , habitat , ecosystem , adaptation (eye) , local adaptation , acclimatization , population , demography , crustacean , neuroscience , sociology
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 ( CT MAX ) 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 CT MAX . We found a higher CT MAX 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 CT MAX . 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.