1. Current address: Lehrstuhl für Tierzucht, Technical University of Munich, D-85354 Freising-Weihenstephan, Germany;
2. Institute of Evolutionary and Ecological Sciences, Leiden University, Kaiserstraat 63, 2300 RA Leiden, The Netherlands
3. Department of Biology, Gilmer Hall, University of Virginia, Charlottesville, Virginia 22904-4328;
4. Biomathematics Research Center, Department of Mathematics and Statistics, University of Canterbury, Christchurch, New Zealand;