1. Ecology, Behavior, and Evolution (EBE), Division of Biology 0116, University of California, San Diego, La Jolla, CA 92092–0116, USA
2. Department of Biology, CB no. 3280 Coker Hall, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599–3280, USA
3. Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18d, SE–752 36 Uppsala, Sweden
4. Department of Biology, Division of Zoology, University of Oslo, PO Box 1050, Blindern, N–0316 Oslo, Norway