1. Centre d‘Ecologie des Systemes Aquatiques Continentaux, UMR C5576, 29, rue Jeanne Marvig, 31055 Cedex 04, France
2. Smithsonian Environmental Research Center, PO Box 28, Edgewater, MD 21037, U.S.A.
3. Flathead Lake Biological Station, University of Montana, Polson, MO 59860, U.S.A.
4. UMR 6553 ECOBIO, Université de Rennes I, Campus de Beaulieu, Batiment 14, 35042 Rennes Cedex, France
5. College of Ocean and Fisheries Sciences, University of Washington, PO Box 357980, Seattle, WA 98195, U.S.A.