1. Department of Biology; Ecology and Evolution; University of Fribourg; Chemin du Musée 10 1700 Fribourg Switzerland
2. Tvärminne Zoological Station; FIN-10900 Hanko Finland
3. Centre d’Ecologie Fonctionnelle et Evolutive - UMR 5175; campus CNRS, 1919, route de Mende 34293 Montpellier Cedex 5 France