1. Canadian Institute for Advanced Research (CIAR) Program in Evolutionary Biology, Department of Biochemistry, Dalhousie University, Halifax, Nova Scotia, B3H 4H7 Canada.
2. CIAR Program in Evolutionary Biology, Institute for Biomedical Computing, Washington University, St. Louis, MO 63110, USA.
3. Department of Biology, Indiana University, Bloomington, IN 47405, USA.