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

Olivier Duron,Pascal Milesi,Célestine M Atyame,Elena V Shaikevich,Mylène Weill,Sandra Unal,Emilie Dumas,Dina M Fonseca,Patrick Makoundou

doi:10.1186/1471-2148-13-181

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.

Highlights

The maternally inherited bacterium Wolbachia often acts as a subtle parasite that manipulates insect reproduction, resulting potentially in reproductive isolation between host populations
Specific ank2 and pk1 PCR assays indicated the occurrence of infection by Wolbachia in all the examined specimens, showing that infection is fixed in all Cx. quinquefasciatus, Cx. p. pipiens form pipiens, Cx. p. pipiens form molestus and Cx. p. pallens populations examined here
Tests for intergenic recombination revealed significant linkage disequilibrium (LD) for ank2 and pk1 (Fisher exact test, P < 10-5): alleles at these loci are not randomly associated showing that they are stably co-transmitted within the wPip chromosome

Summary

Introduction

The maternally inherited bacterium Wolbachia often acts as a subtle parasite that manipulates insect reproduction, resulting potentially in reproductive isolation between host populations. Wolbachia is typically maternally inherited through the egg cytoplasm and has evolved a variety of interactions with its hosts, exerting subtle effects such as manipulation of host reproduction or protection against natural enemies [4,5,6]. In this host, Wolbachia, known as wPip, is associated with cytoplasmic incompatibility (CI), a sperm-egg incompatibility between infected males and uninfected females, so that infected females have a reproductive advantage [7,8,9]. These studies revealed that wPip is an important associate of most mosquitoes in the Cx. pipiens complex potentially driving its evolution

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