1. Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
2. The Roslin Institute at The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Roslin, Midlothian EH25 9PS, UK
3. Instituto de Medicina Preventiva Veterinaria, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
4. Facultad de Ecología Recursos Naturales, Universidad Andrés Bello, Av. República 440, Santiago, Chile