Abstract
The population genetics and phylogenetic relationships of Culex mosquitoes inhabiting the Sonoran Desert region of North America were studied using mitochondrial DNA and microsatellite molecular markers. Phylogenetic analyses of mitochondrial cytochrome c oxidase subunit I (COI) from mosquitoes collected over a wide geographic area, including the Baja California peninsula, and mainland localities in southern Arizona, USA and Sonora, Mexico, showed several well-supported partitions corresponding to Cx. quinquefasciatus, Cx. tarsalis, and two unidentified species, Culex sp. 1 and sp. 2. Culex quinquefasciatus was found at all localities and was the most abundant species collected. Culex tarsalis was collected only at Tucson, Arizona and Guaymas, Sonora. The two unidentified species of Culex were most abundant at Navojoa in southern Sonora. Haplotype and nucleotide diversities in the COI gene segment were substantially lower in Cx. quinquefasciatus compared with the other three species. Analysis of molecular variance revealed little structure among seven populations of Cx. quinquefasciatus, whereas significant structure was found between the two populations of Cx. tarsalis. Evidence for an historical population expansion beginning in the Pleistocene was found for Cx. tarsalis. Possible explanations for the large differences in genetic diversity between Cx. quinquefasciatus and the other species of Culex are presented.
Highlights
The population structure, dispersal capabilities, and systematics of mosquitoes in the genus Culex (Culicidae: Culicinae: Culicini) from the Sonoran Desert of North America are poorly known
Base composition showed little variation among sequences, with CG content averaging 31%. Together these results suggest that our sequences represent mitochondrial DNA (mtDNA) and are not nuclear mitochondrial pseudogenes which have been reported for the c oxidase subunit I (COI) gene in insects [39]
A major finding of this study was that genetic diversity in the COI gene segment of Cx. quinquefasciatus from the Sonoran Desert was much lower than that seen in Cx. tarsalis and Culex sp. 1 and sp. 2 (Table 1)
Summary
The population structure, dispersal capabilities, and systematics of mosquitoes in the genus Culex (Culicidae: Culicinae: Culicini) from the Sonoran Desert of North America are poorly known. Several species reported from this region, including Cx. quinquefasciatus Say, a member of the Cx. pipiens Linnaeus complex, and Cx. tarsalis Coquillett, are important vectors of the West Nile and St. Louis encephalitis viruses that infect humans. Our primary goal in the present study was to utilize mitochondrial DNA (mtDNA) sequences from a segment of the cytochrome c oxidase subunit I (COI) gene, known as the barcode segment [9], to examine population genetics of Culex mosquitoes collected from widely separated localities in the Sonoran Desert region, including the Baja California peninsula, mainland Sonora, Mexico and southeastern Arizona, USA, to test the prediction that Cx. quinquefasciatus and Cx. tarsalis will show evidence of different demographic histories. Because it is well known that taxonomic identifications based on morphological examination of females of certain species of Culex can be especially problematic [5, 10], COI barcodes, which can reliably distinguish many nominal species of Culex [11, 12], were used to estimate the overall biodiversity and phylogenetic relationships of Culex obtained in our survey
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