MBE Advance Access published online on March 5, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm040
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RESEARCH ARTICLE |
Evidence for a Population Expansion in the West Nile Virus Vector Culex tarsalis
* The W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, 21205
Florida Medical Entomology Laboratory, University of Florida, 200 9th St. SE, Vero Beach, FL 32962
The Johns Hopkins Malaria Research Institute, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, 21205
Research conducted at The W. Harry Feinstone Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, 21205
Corresponding author: Jason L. Rasgon, Rm. E4626, Department of MMI, Johns Hopkins Bloomberg School of Public Health, 615 N. Wolfe St. Baltimore, MD 21205. Phone: 410-502-2584, Fax: 410-955-0105. E-mail address: jrasgon{at}jhsph.edu
Received for publication November 27, 2006. Revision received February 20, 2007. Accepted for publication February 26, 2007.
Population genetic structure of the West Nile Virus vector Culex tarsalis was investigated in five states in the western United States using five microsatellite loci and a fragment of the mitochondrial NADH dehydrogenase four (ND4) gene. ND4 sequence analysis revealed a lack of isolation by distance, panmixia across all populations, an excess of rare haplotypes, and a star-like phylogeny. Microsatellites revealed moderate genetic differentiation and isolation by distance, with the largest genetic distance occurring between populations in southern California and New Mexico (FST = 0.146). Clustering analysis and Analysis of Molecular Variance (AMOVA) on microsatellite data indicated the presence of three broad population clusters. Mismatch distributions and site-frequency spectra derived from mitochondrial ND4 sequences displayed patterns characteristic of population expansion. Fu and Li's D* and F*, Fu's FS and Tajima's D statistics performed on ND4 sequences all revealed significant, negative deviations from mutation-drift equilibrium. Microsatellite-based multi-locus heterozygosity tests showed evidence of range expansion in the majority of populations. Our results suggest that C. tarsalis underwent a range expansion across the western United States within the last 375,000-560,000 years, which may have been associated with Pleistocene glaciation events that occurred in the midwestern and western United States between 350,000 and one million years ago.
Key Words: Culex tarsalis • genetic structure • population expansion • West Nile virus