Abstract
Ability to distinguish between closely related Wolbachia strains is crucial for understanding the evolution of Wolbachia-host interactions and the diversity of Wolbachia-induced phenotypes. A useful model to tackle these issues is the Drosophila suzukii – Wolbachia association. D. suzukii, a destructive insect pest, harbor a non-CI inducing Wolbachia ‘wSuz’ closely related to the strong CI-inducing wRi strain. Multi locus sequence typing (MLST) suggests presence of genetic homogeneity across wSuz strains infecting European and American D. suzukii populations, although different Wolbachia infection frequencies and host fecundity levels have been observed in both populations. Currently, it is not clear if these differences are due to cryptic wSuz polymorphism, host background, geographical factors or a combination of all of them. Here, we have identified geographical diversity in wSuz in D. suzukii populations from different continents using a highly diagnostic set of markers based on insertion sequence (IS) site polymorphism and genomic rearrangements (GR). We further identified inter-strain diversity between Wolbachia infecting D. suzukii and its sister species D. subpulchrella (wSpc). Based on our results, we speculate that discernible wSuz variants may associate with different observed host phenotypes, a hypothesis that demands future investigation. More generally, our results demonstrate the utility of IS and GRs in discriminating closely related Wolbachia strains.
Highlights
Wolbachia are obligate-intracellular bacteria infecting more than half of the arthropod species[1]
multi-locus sequence typing (MLST) failed to differentiate between wRi, wSuz and wSpc Wolbachia strains harbored by their natural hosts D. simulans, D. suzukii and D. subpulchrella, respectively[25,26,27]
We designed 34 sets of primers and verified these diagnostic markers by PCR amplification using genomic DNA extracted from D. simulans, D. subpulchrella and two individuals each from thirteen D. suzukii populations (Table 1)
Summary
Wolbachia are obligate-intracellular bacteria infecting more than half of the arthropod species[1]. Wolbachia has been classified in distinct types or strains that can be grouped into at least 16 supergroups (named A–F and H–Q)[19] It is, challenging to distinguish among very closely related bacterial strains using single gene www.nature.com/scientificreports/. The MLST system was insufficient to discriminate closely related Wolbachia strains infecting natural populations of D. melanogaster[13,15,18,24]. According to MLST, different populations of D. suzukii harbor the same wSuz strain, which in turn is indistinguishable from the new strain (wSpc) harbored by D. subpulchrella[26,27] Contrary to their closely related wRi strain that causes strong CI in D. simulans, wSuz and wSpc have been characterized by either very low or a complete lack of CI-inducing capability[26,27]. Unsuccessful determination of hidden wSuz diversity may, under-estimate the actual biological complexities behind wSuz-D. suzukii interactions
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