1. Research Group Behavioural Biology, University of GroningenPO Box 14, 9750 AA Haren, The Netherlands
2. Institute of Zoology—Aquatic Ecology and Macroevolution, University of BernBaltzerstrasse 6, 3012 Bern, Switzerland
3. EAWAG Centre of Ecology, Evolution and Biogeochemistry6047 Kastanienbaum, Switzerland