1. Department of Animal Behaviour; University of Bielefeld; Postfach 100131 33501 Bielefeld Germany
2. British Antarctic Survey; High Cross, Madingley Road Cambridge CB3 OET UK
3. Science of Life Laboratories and Department of Cell and Molecular Biology; Uppsala University; Husargatan 3 75124 Uppsala Sweden
4. Max Planck Institute for Developmental Biology; Spemannstrasse 35 72076 Tübingen Germany
5. Science of Life Laboratories and Department of Evolutionary Biology; Evolutionary Biology Centre; Uppsala University; Norbyvägen 18D 75236 Uppsala Sweden