Contrasting levels of variability between cytoplasmic genomes and incompatibility types in the mosquitoCulex pipiens

Abstract

SUMMARYReproductive incompatibilities called cytoplasmic incompatibilities are known to affect a large number of arthropod species and are mediated by Wolbachia, a maternally transmitted microorganism. The crossing relationships between strains of potential hosts define their incompatibility types and it is generally assumed that differences between strains of Wolbachia induce different crossing types. Among all the described host species, the mosquito, ulex pipiens, displays the greatest variability of cytoplasmic incompatibility crossing types. We analysed mitochondrial and bacterial DNA variability in ulex pipiens in order to investigate some possible causes of incompatibility crossing type variability. We sequenced fragments of the fts gene, and the AjT-rich control region of the mtDNA. We also sequenced the second subunit of the mitochondrial cytochrome oxidase ( OII) gene, in ulex pipiens and a closely related species,. torrentium, in order to verify the usefulness of the AjT-rich region for the present purposes. No variability was found in the Wolbachia fts gene fragment, and very limited variation of the mitochondrial marker whatever the compatibility type or the origin of the host. A low variability was found in the AjTrich region and comparison of divergence of the AjT-rich region and OII gene between . pipiens and . torrentium did not reveal any special constraints affecting this region. In contrast to observations in other host species, variability of incompatibility crossing types is not due to multiple infections by distantly related Wolbachia strains.

Low genetic diversity in Wolbachia-Infected Culex quinquefasciatus (Diptera: Culicidae) from Brazil and Argentina

“…quinquefasciatus and Cx. pipiens mitochondrial genes has been reported by GUILLEMAUD et al 17 . HASAN et al 18 also found low diversity (Hd = 0.502 and π = 0.0007) in the Cx.…”

Hypervariable prophage WO sequences describe an unexpected high number of Wolbachia variants in the mosquito Culex pipiens

“…Barriol and Mart, which displayed identical compatibility towards the other strains, differed from six markers indicating that distinct Wolbachia strains thus do not necessarily generate CI. Matching WO polymorphism to the CI pattern reported in Guillemaud et al (1997) failed to show a correlation, except for Gp15. All crosses between Gp15a strains (Barriol, Espro and Mart, table 3) were fully compatible bi-directionnally.…”

“…This notion was strengthened by the lack of congruence between Wolbachia and phage phylogenies established with the orf7 sequence (ORF Gp3 in our study), suggesting horizontal phage exchange between bacteria co-infecting the same intracellular environment (Bordenstein & Wernegreen 2004;Gavotte et al 2004;Sanogo & Dobson 2004). Since all polymorphic regions found so far in wPip DNA are mobile genetic elements (Sanogo & Dobson 2004;Duron et al 2005), the 'real' Wolbachia genes being monomorphic (Rousset et al 1992;Guillemaud et al 1997;Duron et al 2005), it was proposed that these mobile genetic elements could favour genome fluidity and enhance rapid adaptation, especially in the highly diversified CI system of C. pipiens. For all these reasons we decided to study WO prophage organization and variability in the wPip genome.…”

“…(e) WO prophage and cytoplasmic incompatibilities Previous work by Guillemaud et al (1997) identified four incompatibility types among five C. pipiens strains (Barriol, Mart, Espro, Selax and Sphae). Barriol, Mart, and Espro strains were compatible, whereas Espro and Table 2.…”

“…Crosses between mosquitoes from various origins revealed a high level of incompatibilities (Laven 1951(Laven , 1967Barr 1966;Subbarao 1982;Magnin et al 1987;Guillemaud et al 1997) contrasting with other insect situations (Werren 1998). However, the higher CI level was observed between mosquitoes from Europe, where it exhibits an extreme pattern (Laven 1967;Magnin et al 1987;Guillemaud et al 1997).…”