1. Department of Earth and Environmental Sciences; University of Pavia; via S. Epifanio 14; I-27100; Pavia; Italy
2. Oulanka Research Station; Thule Institute; University of Oulu; Liikasenvaarantie 134; 93999; Kuusamo; Finland
3. Biology Department; University of Oulu; 90014 University of Oulu; Oulu; Finland
4. Institute of Integrative Biology; ETH-Zürich, ETH-Zentrum, Universitätsstrasse 16; CH-8092; Zürich; Switzerland