Evol Ecol Res 16: 517-528 (2014)     Full PDF

Heat tolerance and its evolutionary potential along a latitudinal gradient in Daphnia magna

Aurora N. Geerts, Luc De Meester and Robby Stoks

Department of Biology, KU Leuven, Leuven, Belgium

Correspondence: A.N. Geerts, Department of Biology, KU Leuven, B-3001 Heverlee, Belgium.
e-mail: aurora.geerts@bio.kuleuven.be


Background: Extreme weather events follow latitudinal patterns and are increasing due to climate change. To persist, natural populations must adapt to the increased occurrence of heat waves.

Hypothesis: Heat tolerance is higher at lower latitudes and in smaller animals. Animals show evolutionary potential for heat tolerance.

Organism: The water flea, Daphnia magna, a common species in bodies of fresh water.

Methods: Set up a common-garden experiment using six populations spread across three latitudes in Western Europe, thereby creating a latitudinal gradient in local temperatures. Measure CTmax, the temperature above which animals lose motor function.

Results: Thermal tolerance increased with increasing local temperatures. Body size, which was smaller at the southern latitude, negatively affected heat tolerance. Heat tolerance showed genetic variation within latitudes.

Conclusions: Daphnia magna possesses the evolutionary potential to increase its heat tolerance if temperatures warm. Its heat tolerance shows latitudinal adaptation to local temperatures. A parallel pattern in body size magnifies the latitudinal pattern in heat tolerance.

Keywords: CTmax, Daphnia magna, evolutionary potential, latitude, thermal adaptation.



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