1. Department of Plant and Microbial Biology; University of California; Berkeley CA 94720 USA
2. Laboratoire d'Ecologie; Systematique et Evolution; Bâtiment 360; 91405 Orsay France
3. CNRS; Bâtiment 360; 91405 Orsay France
4. Department of Integrative Biology; University of California; Berkeley CA 94720 USA
5. Department of Energy; Joint Genome Institute; 2800 Mitchell Dr.; Walnut Creek CA 94598 USA
6. Department of Biology; Duke University; Durham NC 27708 USA
7. Department of Biology; Stanford University; Stanford CA 94305 USA