The major ongoing and newest project is a worldwide genetic analyses of populations of Aedes aegypti, “the yellow fever mosquito”, although today it is of most concern as the major vector of dengue fever. We are studying three aspects of this mosquito:
➢ We are analyzing the population genetic structure of the species by surveying 100+ population samples from throughout its distribution: worldwide from about 35° N and S latitudes. This employs a battery of highly variable microsatellites and DNA sequence data for ~4 kb of variable introns. This work is a combination of population structure analysis, phylogeography, and evolutionary history addressing such issues as degree of differentiation and temporal genetic stability of populations, rates of migration among populations, patterns of spread of the mosquito, and whether different ecotypes and morphologies have evolved more than once. We are beginning RAD-tag analyses of populations to use NextGen sequencing methods to identify 1000s of SNPs to refine our population genetics work.
➢ Once we have determined the patterns of genetic differentiation of the species, in collaboration with the University of Florida, ~25 populations representative of the major genetic subdivisions will be studied for their ability to transmit the dengue virus. There is considerable geographic heterogeneity in human dengue incidence and it is likely that that this is at least partially due to the genetic heterogeneity of Aedes aegypti in its capacity to transmit the virus. We are using next generation high throughput DNA sequencing technology to study the variation in 100+ genes that lab studies have indicated are involved in the mosquito’s ability to replicate and transmit the virus.
Ultimately, we hope to demonstrate that sufficient naturally occurring genetic variation in ability to transmit dengue exists and that control of human dengue can be accomplished by increasing the frequencies of existing genotypes unable to transmit the virus, by-passing lab manipulations that debilitate the mosquito, making it less fit and thus less likely to spread genes. We will also determine whether the naturally-occurring resistant genotypes are different in different regions of the distribution of Aedes aegypti, thus indicating region-specific control strategies are needed.
At present we have two publications on the new Aedes aegypti work (numbers 1 and 21 in list of 2007-2010 publications). Two more publications are in preparation, one describing the genetic differentiation between sympatric forms of Aedes aegypti in Kenya, including differences in host choice for blood meals, this last aspect being collaboration with colleagues at The Rockefeller University. A second manuscript analyzes the temporal stability and instability of populations that varies depending on ecological setting and human interventions. Two more publications are in preparation, one describing the genetic differentiation between sympatric forms of Aedes aegypti in Kenya, including differences in host choice for blood meals, this last aspect being a collaboration with colleagues at The Rockefeller University. A second manuscript analyzes the temporal stability and instability of populations that varies depending on ecological setting and human interventions.
We are completing a major project on the molecular evolution of genes involved in innate immunity of mosquitoes and their relationship to the ability to transmit malaria. Using an evolutionary approach, we identify those insect immunity genes that specifically control the ability to transmit the most deadly form of malaria, that caused by Plasmodium falciparum. This work is reported in publications 7, 9, 11, 18 in 2007-2010 publication list with two more manuscripts in preparation.
We also have interest in the invasive potential of members of the Anopheles gambiae which is the most important vector of malaria in the world and is largely confined to sub-Saharan Africa. It has the potential to escape Africa, and has done so in the past. In this context, we determined which of the cryptic species of this group invaded Brazil in the 1930s; the invasion occurred in 1940 and was eradicated by 1940. Analysis of DNA from museum specimens collected in the 1930s in Brazil revealed that the invader wasAnopheles arabiensis, an unrecognized species in at the time and the most dry-adapted member of the group.
Graduate student Michael Ready is conducting his dissertation research on Anopheline malaria vectors in Equatorial Africa. See http://www.yale.edu/powell/people_reddy.html
Select papers on Anopheles from the Powell lab prior to 2007
della Torre, A., C. Costantini, N. J. Besansky, A Caccone, V. Petrarca, J. R. Powell and M. Coluzzi. 2002, Speciation within Anopheles gambiae—The glass is half full. Science 298:115-117. A general discussion of the issues of speciation in the most important malaria vectors in the world. Abstract
Slotman, M. A., A. della Torre, and J. R. Powell. 2005. Female sterility in hybrids between Anopheles gambiae and An. arabiensis and causes of Haldane’s rule. Evolution 59:1016-1026. A QTL-based analyses of the genetics of reproductive isolation among malaria vectors. Abstract
Marshall, J. C., A. Caccone, J. R. Powell. 2005. Phylogenetic relationships of five major Plasmodium falciparum vectors within the mosquito subgenus Cellia. Am. J. Trop. Med. Hyg. 73:749-752. A molecular phylogeny of all the major vectors of malaria in sub-Saharan Africa where 95% of all malaria deaths occur. Abstract