FOREST AND DOMESTIC FORMS OF THE DENGUE FEVER MOSQUITO
Researchers investigating the outbreak of an unknown illness along the coast of East Africa in 1952 discovered homes populated by a brown ‘domestic’ form of the mosquito Aedes aegypti . A black ancestral ‘forest’ form of the same species was later found breeding in forests, just hundreds of meters away. Although closely related and fully interfertile in the laboratory, the two forms remained distinct in the wild and showed striking divergence in behavior: Domestic females readily entered homes, were strongly attracted to human odor, and laid their eggs in water-storage containers indoors. Forest females avoided homes, preferred the odor of non-human animals, and laid their eggs in tree holes outdoors. These behavioral differences translated into marked divergence in capacity to spread human diseases, such as Chikungunya, the unknown illness from 1952, yellow fever, prevalent in Africa and South America since the 16th century, dengue fever, currently causing sickness in over 300 million people around the world each year, and zika.
Forest and domestic populations of Aedes aegypti still coexist in Rabai, Kenya today and provide a unique opportunity to study adaptive behavioral evolution in a model ammenable to genomic, molecular, and neuroscientific studies. The species is easy to rear in the laboraty and has a short 3-week generation time. It also has a fully sequenced genome and is open to genetic manipulation. Using CRISPR/Cas9 technology, it is now relatively easy to create transgenic strains where specific genes of interest have been knocked out and/or exogenous sequences knocked-in. It is also close enough to Drosophila that many of the same tools and knowledge can be transferred, including the tools needed for modern neuroscientific approaches such as brain imaging using genetically encoded calcium sensors.
THE WEST NILE VIRUS VECTOR Culex pipiens
The northern house mosquito, Culex pipiens, is a major vector of West Nile Virus and lymphatic filariasis. It is found in temperate regions across the world. Like Aedes aegypti, Cx. pipiens also includes ecologically divergent forms. Culex pipiens form pipiens is cold-adapted, requires a blood meal to lay eggs, and primarily bites birds. Culex pipiens form molestus is warm-adapted, can lay its first clutch without a blood meal, and, at least in some places, primarily bites mammals. Intriguingly, molestus can exist alongside pipiens in the colder northern latitudes of Europe and North America, by living below ground in urban subway systems and basements. We are taking genomic approaches to understand the origin and evolution of this interesting species, as well as the genetic basis of bird- versus mammal-biting.