1. Program in Evolutionary Biology, Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, Ontario M5G 1Z8, Canada
2. Département de Biochimie, Université de Montréal, 2900 Boulevarde Edouard-Montpetit, Montréal, Québec H3T 1J4, Canada
3. Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada