DISSERTATION RESEARCH: The Genomics of Hybrid Sterility & Speciation in the Anopheles gambiae Species Complex

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This project will investigate genetic mechanisms driving speciation in a group of mosquitos known to transmit disease. In this group of mosquitos the number of different species has traditionally been underestimated because, while indistinguishable in appearance, the group is actually comprised of multiple genetically distinct species. Despite their importance to humans little is known about how these species arose. This project addresses three questions in mosquito genetics. First what genes are responsible for reproductive isolation between the species? Second, how do those genes diverge across time leading to speciation? And third is the pattern of change between two species consistent across different pairs of species? Several of these species are the major vectors of human malaria in sub-Saharan Africa. In addition to helping us understand the genetic process that creates biological diversity, this project therefore has additional societal benefits as it may help in the development and implementation of novel genetic vector control measures by, identifying genes causing sterility in mosquitoes.The name Anopheles gambiae is actually associated with a species complex of eight genetically distinct but recently diverged species that cannot be identified based on morphology. The complex is an important study system for the field of speciation genetics because species in the complex exhibit a wide range of genetic divergence, including partially isolated sub-species. Therefore this species complex allows these researchers to study speciation as it unfolds. When different species of the complex hybridize, the male offspring are sterile and females are fertile. If a hybrid female mates with a male of either parental species, the resulting second-generation hybrids exhibit varying levels of sterility due to genetic incompatibility. This allows genomic mapping of the causes of sterility through sequencing of many backcross offspring. This study will thereby map regions of the genome that cause male and female sterility in backcross hybrids between two species (An. gambiae and An. quadriannulatus). Combined with existing data on male and female sterility in backcross hybrids between An. gambiae and An. arabiensis this data will determine if the same genomic regions cause sterility across different species pairs. By comparing the patterns of divergence and their causes across multiple species pairs the research will increase our understanding of the factors driving speciation in an important group of animals.