Population genetics and vector competence of Aedes aegypti in West Africa
Date
2014
Authors
Dickson, Laura B., author
Black, William C., IV, advisor
Miller, Barry, committee member
Foy, Brian, committee member
Blair, Carol, committee member
Huyvaert, Kate, committee member
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Abstract
The mosquito, Ae. aegypti is the primary vector for all four serotypes of dengue (DENV 1-4) and yellow fever viruses worldwide. Dengue remains an important public health problem with an estimated 390 million cases per year and yellow fever outbreaks are still continuously reported even though a safe and effective vaccine exists. Aedes aegypti (L) is found globally in tropical and sub-tropical climates and exists as two subspecies: Ae. aegypti aegypti (Aaa) and Ae. aegypti formosus (Aaf) which have previously been defined by the presence or absence of scales on the first abdominal tergite. This classification system was developed in East Africa and is contradictory in West Africa where this mosquito is genetically diverse and exhibits great variation in susceptibility to DENV and YFV, which is a quantitative genetic trait. Understanding the population genetics, the vector competence, and the way in which genetic diversity contribute to vector competence of Ae. aegypti can improve our general understanding of mosquito/virus interactions and lead to potential ways to control these mosquitoes in nature. In this dissertation, the distribution of FST values calculated from deep sequencing data between mosquitoes from two diverse locations in Senegal, one location in Mexico, and one location in Thailand across the entire genome were compared to identify the degree of genomic divergence as well as identify genes involved in speciation between the various populations. The distribution of FST values were also compared in different gene regions and mutation types to identify which parts of the genome provide the greatest resolution of subspecies population structure. Genetic crossing experiments and deep sequencing of the sex determining locus of Ae. aegypti from Senegal and Thailand was used to demonstrate discrete genetic differences between the subspecies. The vector competence for a local sylvatic isolate of DENV-2 and two genetically diverse YFV isolates was compared between various collections of Ae. aegypti throughout Senegal to demonstrate that vector competence in these mosquitoes is dependent on the viral isolate. The genetic diversity of an important immune sensing gene, Dcr2 of the exo-siRNA pathway, was determined from mosquitoes with various vector competence phenotypes to test how the genetic diversity of this gene in individuals and populations of mosquitoes contribute to vector competence. Overall, data in this dissertation suggest 1) allopatric speciation between Ae. aegypti from Senegal and Mexico or Thailand, and sympatric speciation within Senegal based on the distributions of FST values and variations in the sex determining locus between populations, 2) vector competence of Ae. aegypti from Senegal is dependent on the flavivirus species and viral genotype, and 3) increased genetic diversity of Dcr2 in individual Ae. aegypti, but not from populations of Ae. aegypti, from Senegal is correlated with the ability of Ae. aegypti to control DENV-2 infection. These results aid in our general understanding of the role of genomic divergence in speciation, as well as our understanding of genetics, vector competence, and the genetics of vector competence of West African Ae. aegypti, which could provide insight into the way we identify subspecies and make predictions about vector competence in this region.
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Subject
yellow fever
dengue
Aedes aegypti