Acknowledgments
We thank Prof. Walter Lämmler for his efforts maintaining the Landolt duckweed collection and for providing us with the strains used in this experiment. Thanks to Owen Petchey and the whole Petchey group for advice and Yves Choffat for technical support in the lab. Sofia Vamos provided helpful feedback on the manuscript. This study was funded by the University of Zurich (Forschungskredit 31259 awarded to S.J.V.M.)