Wolbachia in Culex pipiens: Is there a relationship between Wolbachia strains and population substructuring or host selection?

Wolbachia are endosymbiotic bacteria which infect many different organisms, including Culex pipiens mosquitoes.  Owing to the bacteria’s self-perpetuation mechanisms such as cytoplasmic incompatibility (CI) leading to mating incompatibility, Wolbachia infections may result in population substructuring of their insect hosts.  This may especially be true if different strains of Wolbachia circulate within the same host species.  To date, however, identifying and classifying strains of Wolbachia has proven problematic, as it has been difficult to isolate a region of the Wolbachia genome which shows sufficient polymorphism to account for the many types of CI observed.  Recently, it was found that sequences in the mobile prophage WO may present a good target for strain analysis.  In this study, Culex pipiens mosquitoes collected from the Oak Lawn area of Chicago, IL in 2005 and 2006 were analyzed based on sequences of 10 WO prophage marker genes, yielding 50 unique marker profiles.  There was no relationship between presence of WO type and genetic ancestry based on prior analysis for Culex pipiens molestus heritage, nor with mammal vs. avian host selection tendency.  These results suggest that Wolbachia prophage genotypes are apportioned independently of C. pipiens genetic heritage or feeding preference, implying that the WO marker genes studied are not good indicators of genetic substructuring or host selection.