Department of Mathematics, University of Nebraska-Lincoln, Lincoln, NE, United States of America.|Department of Mathematics, University of California Irvine, Irvine, CA, United States of America.|Center for Complex Biological Systems, University of California Irvine, Irvine, CA, United States of America.|Center for Complex Biological Systems, University of California Irvine, Irvine, CA, United States of America.|Center for Complex Biological Systems, University of California Irvine, Irvine, CA, United States of America.|Department of Mathematics, University of California Irvine, Irvine, CA, United States of America.