Abstract
BackgroundWolbachia is one of the most widespread bacteria on Earth. Previous research on Wolbachia-host interactions indicates that the bacterium is typically transferred vertically, from mother to offspring, through the egg cytoplasm. Although horizontal transmission of Wolbachia from one species to another is reported to be common in arthropods, limited direct ecological evidence is available. In this study, we examine horizontal transmission of Wolbachia using a multilocus sequence typing (MLST) strains dataset and used Wolbachia and Lepidoptera genomes to search for evidence for lateral gene transfer (LGT) in Lepidoptera, one of the most diverse cosmopolitan insect orders. We constructed a phylogeny of arthropod-associated MLST Wolbachia strains and calibrated the age of Wolbachia strains associated with lepidopteran species.ResultsOur results reveal inter-specific, inter-generic, inter-familial, and inter-ordinal horizontal transmission of Wolbachia strains, without discernible geographic patterns. We found at least seven probable cases of horizontal transmission among 31 species within Lepidoptera and between Lepidoptera and other arthropod hosts. The divergence time analysis revealed that Wolbachia is recently (22.6–4.7 mya, 95 % HPD) introduced in Lepidoptera. Analysis of nine Lepidoptera genomes (Bombyx mori, Danaus plexippus, Heliconius melpomene, Manduca sexta, Melitaea cinxia, Papilio glaucus, P. polytes, P. xuthus and Plutella xylostella) yielded one possible instance of Wolbachia LGT.ConclusionsOur results provide evidence of high incidence of identical and multiple strains of Wolbachia among butterflies and moths, adding Lepidoptera to the growing body of evidence for common horizontal transmission of Wolbachia. This study demonstrates interesting dynamics of this remarkable and influential microorganism.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0660-x) contains supplementary material, which is available to authorized users.
Highlights
Wolbachia is one of the most widespread bacteria on Earth
Some of the strains from lepidopteran hosts (16/90) were unnamed and incomplete because not all five of the multilocus sequence typing (MLST) loci were sequenced; these strains were designated as unassigned (UA) strains (Additional file 3: Table S3), and we included them in our analysis as such
MLST strain diversity in Lepidoptera All Wolbachia strains with known associated lepidopteran hosts were grouped in either Supergroup A or B
Summary
Wolbachia is one of the most widespread bacteria on Earth. Previous research on Wolbachia-host interactions indicates that the bacterium is typically transferred vertically, from mother to offspring, through the egg cytoplasm. We constructed a phylogeny of arthropod-associated MLST Wolbachia strains and calibrated the age of Wolbachia strains associated with lepidopteran species. Offspring vertically inherit both nuclear and non-nuclear genetic material from their mothers [1]. Among the non-nuclear material inherited are intracellular bacteria which are transferred vertically from mother to offspring and often live in symbioses with their hosts [2]. These symbionts may be obligate (essential for host survival) or facultative, in which case they can increase or decrease host fitness [3, 4]. Horizontal transmission is thought to be the most likely explanation for closely related symbionts occurring in
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