Transfer of genetic material across hybrid zones in the Culex pipiens complex

Although hybridization events have now been documented in multiple vector species, the importance of hybridization to the changing landscape of infectious diseases is a controversial subject that deserves to be examined in detail. We have uncovered an unexpected asymmetric introgression of genetic material between species in the Culex pipiens complex in Asia (Cx. pipiens pallens and Cx. quinquefasciatus) and in Australia (Cx. globocoxitus and Cx. quiquefasciatus). A large genomic region (>500kb) of Cx. quinquefasciatus, that includes the male determining locus, has been incorporated only into male Cx. p. pallens and Cx. globocoxitus (creating Cx. australicus). Introgression at the male locus may explain the “hybrid” genitalia characteristic of both Cx. p. pallens and Cx. australicus. We have mapped the boundaries of the genomic region from Cx. quinquefasciatus that has introgressed into Cx. p. pallens, and examined the patterns of expression of a putative male determining locus located within this genomic region. We have also examined the role of the cytoplasmic bacterium Wolbachia pipientis in the process of speciation. Our results provide a previously unknown pathway to examining ancient hybridization and the fate of the resulting hybrids. Our work provides key insights into the transfer of genetic material across a hybrid zone of important disease vectors, leading to the identification of important genes affecting life history and ultimately vectorial capacity.