1. Department of Ecology and Evolution, The University of Chicago, Chicago, Illinois 60637;
2. Committee on Genetics, Genomics, and Systems Biology, The University of Chicago, Chicago, Illinois 60637;
3. Department of Biology and the Koch Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139;
4. Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil 05508;