1. Institute of Biodiversity, Animal Health and Comparative Medicine, Scottish Centre for Ecology and the Natural Environment, University of Glasgow, Rowardennan G63 0AW, UK
2. Department of Biology, Section for Evolutionary Ecology, Lund University, SE-223 62 Lund, Sweden
3. Institute for Biodiversity, Animal Health and Comparative Medicine, Graham Kerr Building, University of Glasgow, Glasgow G12 8QQ, UK