1. Department of Biological Sciences, Imperial College London, Silwood Park, Ascot SL5 7PY, U.K.
2. Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, U.K.
3. Lehrstuhl für Tierzucht, Technical University of Munich, Alte Akademie 12, 85354 Freising‐Weihenstephan, Germany