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
We are also interested in other mosquito models, including Culex pipiens – the primary vector of West Nile Virus in North America. This species also comprises distinct varieties or forms with divergent behavior – the bird biting Culex pipiens pipiens and the mammal biting Culex pipiens molestus. The two forms remain distinct in many parts of the native range in Europe but undergo extenstive hybridization where they have been introduced in North America.