Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2008
Publication Date: 3/1/2009
Citation: Kothera, L., Zimmerman, E.M., Richards, C.M., Savage, H.M. 2009.Microsatellite characterization of subspecies and their hybrids in Culex pipiens complex mosquitoes along a north-south transect in the central United States of America. Journal of Medical Entomology 46:236-248.
Interpretive Summary: This study identifies a region of hybridization that occurs between two subspecies of mosquito found in the central United States. We apply a set of non hierarchical methods for parsing out the individuals that have a hybrid history and use graphical methods to display this genetic structure. These methods have identified a hybrid zone that exceed the range predicted by morphological traits alone. These results have important implications for managing the spread of West Nile disease.
Technical Abstract: Mosquitoes in the Culex pipiens complex, Cx. p. pipiens L. (Cpp) and Cx. p. quinquefasciatus Say (Cpq), are morphologically similar and important vectors of the West Nile and St. Louis Encephalitis viruses in the US. They hybridize when found in sympatry, which could facilitate the transfer of advantageous alleles between taxa. However, the subspecies differ ecologically, with Cpp entering diapause in response to winter conditions and Cpq lacking this ability. Specimens were collected using gravid traps set along a transect from New Orleans, LA to Chicago, IL. This study used microsatellite markers to: genetically characterize the subspecies and hybrids, determine the degree and extent of hybridization in order to better define the limits of the hybrid zone, and compare the ability to detect hybrids between microsatellites and a single-gene assay based on the acetylcholinesterase.2 gene (HotAce.2). Genetic diversity and differentiation were consistent with two genetically distinct taxa contributing to a hybrid zone. Most departures from HWE were found within the hybrid zone, and expected heterozygosity was highest there as well. There was a significant isolation by distance effect, and AMOVA results suggest gene flow occurs primarily between adjacent sites. Admixture analyses classified more than 40% of individuals as hybrids, and as a result we propose new boundaries to the hybrid zone compared to those indicated by a previous study. Microsatellites detected more hybrids than the HotAce.2 assay, although the latter remains useful as a screening tool. We propose the limits of the hybrid zone are maintained by selection for diapause.