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United States Department of Agriculture

Agricultural Research Service

Research Project: Population Genetics of North American Rift Valley Fever Disease Vectors

Location: Arthropod-Borne Animal Diseases Research

2013 Annual Report


1a.Objectives (from AD-416):
The goal of this study is to quantify the population structure of the mosquito species of medical and veterinary importance in North America, Culex tarsalis (Coquillett) and Aedes vexans (Meigen). The objective is to associate identified genotypes with geographic locations and disease vector competence.


1b.Approach (from AD-416):
Culex tarsalis and Ae. vexans mosquitoes were selected for several reasons. (1) One or both species are vector competent to transmit many viruses, including West Nile, Rift Valley Fever, Japanese B and Saint Louis encephalitis, and Eastern, Western, and Venezuelan equine encephalitis viruses; (2) The species opportunistically feed on both mammals and birds and potentially serves as a bridge vector between distinct host groups; and (3) The species have a long dispersal distance and extensive geographic distribution (coast to coast and from the Southern United States into Canada) which creates a large at-risk area. Throughout their range one or both species of mosquito have been characterized by phenotypic variation in virus susceptibility, horizontal and vertical virus transmission, autogeny, and host preference. However, the observed phenotypic variation is currently unlinked to genetic or geographic groupings, despite previous studies examining population structure using allozyme, five microsatellite and mitochondrial markers. Finding appropriate genetic markers for this non-model organism has been difficult because of the relatively recent expansion (~22,000 years) throughout the North American continent.

Mosquitoes from at least 150 locations throughout their known distributions will be collected for a population genetics analysis. The genomic DNA from at least ten individuals from each collection location will be pooled and used for the identification of single nucleotide polymorphisms (SNPs) using restriction-site-associated DNA tags (RAD-tags) and 454-sequencing. The SNPs will be used with phyogenetics and population genetics techniques to describe the historical range expansion and to quantify the number of existing mosquito populations and the migration rates between them.


3.Progress Report:

The objective of this agreement is to understand the phylogenetic history and population genetics of important disease vector mosquitoes, specifically Aedes vexans and Culex tarsalis No additional funds were spent on this project, although sequencing was completed sufficiently to determine the origins and subsequent geographic radiation of Culex tarsalis throughout the Western United States. Aedes vexans populations are currently being sequenced and analyzed.


Last Modified: 7/31/2014
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