1. Aberdeen Population Ecology Research Unit (APERU), Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ,
2. NERC Molecular Genetics in Ecology Initiative, Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen, AB24 2TZ,
3. Centre for Ecology and Hydrology, Banchory Research Station, Hill of Brathens, Banchory AB31 4BW, UK