Population structure of Wolbachia and cytoplasmic introgression in a complex of mosquito species

Abstract

BackgroundThe maternally inherited bacterium Wolbachia often acts as a subtle parasite that manipulates insect reproduction, resulting potentially in reproductive isolation between host populations. Whilst distinct Wolbachia strains are documented in a group of evolutionarily closely related mosquitoes known as the Culex pipiens complex, their impact on mosquito population genetics remains unclear. To this aim, we developed a PCR-RFLP test that discriminates the five known Wolbachia groups found in this host complex. We further examined the Wolbachia genetic diversity, the variability in the coinherited host mitochondria and their partitioning among members of the Cx. pipiens complex, in order to assess the impact of Wolbachia on host population structure.ResultsThere was a strong association between Wolbachia and mitochondrial haplotypes indicating a stable co-transmission in mosquito populations. Despite evidence that members of the Cx. pipiens complex are genetically distinct on the basis of nuclear DNA, the association of Wolbachia and mtDNA with members of the Cx. pipiens complex were limited. The Wolbachia wPip-I group, by far the most common, was associated with divergent Cx. pipiens members, including Cx. quinquefasciatus, Cx. pipiens pipiens form pipiens and Cx. pipiens pipiens form molestus. Four other wPip groups were also found in mosquito populations and all were shared between diverse Cx. pipiens members.ConclusionThis data overall supports the hypothesis that wPip infections, and their allied mitochondria, are associated with regular transfers between Cx. pipiens members rather than specific host associations. Overall, this is suggestive of a recent and likely ongoing cytoplasmic introgression through hybridization events across the Cx. pipiens complex.

Wolbachia Divergence and the Evolution of Cytoplasmic Incompatibility in Culex pipiens

“…pipiens distribution range: w Pip-I and w Pip-III are largely spread over different continents, whereas w Pip-II is restricted to Western Europe, w Pip-V to Asia, and w Pip-IV sporadically present in Europe, Asia and North Africa [22]. We then asked whether the large geographic distribution of the w Pip-I and w Pip-III groups could be due to more invasive CI properties.…”

Molecular data reveal a cryptic species within the Culex pipiens mosquito complex

“…The pattern of mtDNA variation within the C. pipiens complex is known to be confounded by the spread of Wolbachia : both are linked through maternal cotransmission within egg cytoplasm, resulting in complete linkage disequilibrium of mtDNA with w Pip infection (Rasgon et al ., ; Atyame et al ., ; Dumas et al ., ). The invasion of the w Pip ancestor within the last 20 000 years resulted in an indirect selective sweep of the mtDNA, which has led to the loss of mtDNA variation within host populations and erased any geographical structure (Rasgon et al ., ; Atyame et al ., ; Dumas et al ., ).…”

“…The second species, C. quinquefasciatus , is rather found across the tropics and the lower latitudes of temperate regions. Both species, including all the subspecies and forms, are infected by w Pip with infection frequencies near or at fixation in field populations (Rasgon & Scott, ; Duron et al ., ; Dumas et al ., ). This infection pattern is well explained by the ability of w Pip‐infected males to induce complete CI with uninfected females, a near perfect maternal transmission of infection and a reduced effect on female fecundity (Rasgon & Scott, ; Duron et al ., ).…”

Wolbachia-Based Population Control Strategy Targeting Culex quinquefasciatus Mosquitoes Proves Efficient under Semi-Field Conditions

“…However, w Pip strains display a high genetic polymorphism at a small evolutionary scale and five w Pip groups (referred to as w Pip-I to V) are currently recognized [29, 30]. Interestingly, very low Wolbachia diversity was found in natural populations of Cx .…”