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Male-killing Wolbachia and mitochondrial selective sweep in a migratory African insect.

ABSTRACT: BACKGROUND:Numerous recent studies have shown that resident symbiotic microorganisms of insects play a fundamental role in host ecology and evolution. The lepidopteran pest, African armyworm (Spodoptera exempta), is a highly migratory and destructive species found throughout sub-Saharan Africa, that can experience eruptive outbreaks within the space of a single generation, making predicting population dynamics and pest control forecasting extremely difficult. Three strains of Wolbachia have recently been identified infecting this species in populations sampled from Tanzania. In this study, we examined the interaction between Wolbachia pipiensis infections and the co-inherited marker, mtDNA, within populations of armyworm, as a means to investigate the population biology and evolutionary history of Wolbachia and its host. RESULTS:A Wolbachia-infected isofemale line was established in the laboratory. Phenotypic studies confirmed the strain wExe1 as a male-killer. Partial sequencing of the mitochondrial COI gene from 164 individual field-collected armyworm of known infection status revealed 17 different haplotypes. There was a strong association between Wolbachia infection status and mtDNA haplotype, with a single dominant haplotype, haplo1 (90.2% prevalence), harbouring the endosymbiont. All three Wolbachia strains were associated with this haplotype. This indicates that Wolbachia may be driving a selective sweep on armyworm haplotype diversity. Despite very strong biological and molecular evidence that the samples represent a single species (including from nuclear 28S gene markers), the 17 haplotypes did not fall into a monophyletic clade within the Spodoptera genus; with six haplotypes (2 each from 3 geographically separate populations) differing by >11% in their nucleotide sequence to the other eleven. CONCLUSIONS:This study suggests that three strains of Wolbachia may be driving a selective sweep on armyworm haplotype diversity, and that based on COI sequence data, S. exempta is not a monophyletic group within the Spodoptera genus. This has clear implications for the use of mtDNA as neutral genetic markers in insects, and also demonstrates the impact of Wolbachia infections on host evolutionary genetics.

SUBMITTER: Graham RI

PROVIDER: S-EPMC3557208 | biostudies-literature | 2012 Oct

REPOSITORIES: biostudies-literature

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Male-killing Wolbachia and mitochondrial selective sweep in a migratory African insect.

Graham Robert I RI Wilson Kenneth K

BMC evolutionary biology 20121015

<h4>Background</h4>Numerous recent studies have shown that resident symbiotic microorganisms of insects play a fundamental role in host ecology and evolution. The lepidopteran pest, African armyworm (Spodoptera exempta), is a highly migratory and destructive species found throughout sub-Saharan Africa, that can experience eruptive outbreaks within the space of a single generation, making predicting population dynamics and pest control forecasting extremely difficult. Three strains of Wolbachia h ...[more]

PMID: 23061984

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Project description:BackgroundEvolutionary processes can cause strong spatial genetic signatures, such as local loss of genetic diversity, or conflicting histories from mitochondrial versus nuclear markers. Investigating these genetic patterns is important, as they may reveal obscured processes and players. The maternally inherited bacterium Wolbachia is among the most widespread symbionts in insects. Wolbachia typically spreads within host species by conferring direct fitness benefits, and/or by manipulating its host reproduction to favour infected over uninfected females. Under sufficient selective advantage, the mitochondrial haplotype associated with the favoured maternally-inherited symbiotic strains will spread (i.e. hitchhike), resulting in low mitochondrial genetic variation across the host species range.MethodThe common bluetail damselfly (Ischnura elegans: van der Linden, 1820) has recently emerged as a model organism for genetics and genomic signatures of range expansion during climate change. Although there is accumulating data on the consequences of such expansion on the genetics of I. elegans, no study has screened for Wolbachia in the damselfly genus Ischnura. Here, we present the biogeographic variation in Wolbachia prevalence and penetrance across Europe and Japan (including samples from 17 populations), and from close relatives in the Mediterranean area (i.e. I. genei: Rambur, 1842; and I. saharensis: Aguesse, 1958).ResultsOur data reveal (a) multiple Wolbachia-strains, (b) potential transfer of the symbiont through hybridization, (c) higher infection rates at higher latitudes, and (d) reduced mitochondrial diversity in the north-west populations, indicative of hitchhiking associated with the selective sweep of the most common strain. We found low mitochondrial haplotype diversity in the Wolbachia-infected north-western European populations (Sweden, Scotland, the Netherlands, Belgium, France and Italy) of I. elegans, and, conversely, higher mitochondrial diversity in populations with low penetrance of Wolbachia (Ukraine, Greece, Montenegro and Cyprus). The timing of the selective sweep associated with infected lineages was estimated between 20,000 and 44,000 years before present, which is consistent with the end of the last glacial period about 20,000 years.ConclusionsOur findings provide an example of how endosymbiont infections can shape spatial variation in their host evolutionary genetics during postglacial expansion. These results also challenge population genetic studies that do not consider the prevalence of symbionts in many insects, which we show can impact geographic patterns of mitochondrial genetic diversity.

Dataset Information

Male-killing Wolbachia and mitochondrial selective sweep in a migratory African insect.

Publications

Male-killing Wolbachia and mitochondrial selective sweep in a migratory African insect.

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