Department of Integrative Biology, UC Berkeley, Berkeley, CA 94720, USA, Institute of Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK and Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.|Department of Integrative Biology, UC Berkeley, Berkeley, CA 94720, USA, Institute of Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT, UK and Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.