1. Department of Animal Development and Genetics, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, Uppsala SE–752 36, Sweden
2. Department of Zoology, Stockholm University, Stockholm SE–106 91, Sweden
3. Norwegian College of Fisheries Science, University of Tromsø, Tromsø N–9037, Norway
4. Department of Comparative Physiology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18A, Uppsala SE–752 36, Sweden