Department of Biology, Georgetown University, Washington, DC, United States of America.|Department of Mathematics & Statistics, Georgetown University, Washington, DC, United States of America.|Department of Biology, Georgetown University, Washington, DC, United States of America.|Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.|Fogarty International Center, National Institutes of Health, Bethesda, Maryland, United States of America.|Department of Biology, Georgetown University, Washington, DC, United States of America.