1. Department of Biology, University of Maryland, College Park, MD 20742, USA
2. Rocky Mountain Biological Laboratory, PO Box 519, Crested Butte, CO 81224, USA
3. Department of Bioscience, Aarhus University, Grenåvej 14, 8410 Rønde, Denmark
4. Arctic Research Centre, Aarhus University, C. F. Møllers Allé 8, 8000 Aarhus C, Denmark
5. Department of Bioscience, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark