1. Department of Biology, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway
2. University of Maryland School of Medicine and Institute of Human Virology, Room 552, Medical Biotechnology Centre, 725 West Lombard Street, Baltimore, MD 21201, USA
3. Center for Applied Aquatic Ecology, North Carolina State University, Suite 104, 620 Hutton Street, Raleigh, NC 27606-7510, USA