1. Department of Veterinary Biosciences (G.S.P., Y.-P.C., A.K., Q.L., S.R.M., I.C.B.), Urbana, Illinois 61802;
2. Department of Molecular and Integrative Physiology (J.K., M.S., M.K.B.), University of Illinois at Urbana-Champaign, Urbana, Illinois 61802;
3. Population Council (R.L.S.-W.), New York, New York 10021