Abstract
ObjectiveMutualism between endogenous viruses and eukaryotes is still poorly understood. Several endogenous double-stranded polydnaviruses, bracoviruses, homologous to those present in parasitic braconid wasp genomes were detected in the tsetse fly (Glossina morsitans morsitans). This is peculiar since tsetse flies do not share a reproductive lifestyle similar to wasps, but deliver fully developed larvae that pupate within minutes of exiting their mothers. The objective of this study is to investigate genomic distribution of bracoviral sequences in five tsetse fly species and the housefly, and examine its value as a potential vector control strategy target point. We use comparative genomics to determine the presence, distribution across Glossina species genomes, and evolutionary relationships of bracoviruses of five tsetse fly species and the housefly.ResultsWe report on homologous bracoviruses in multiple Dipteran genomes. Phylogenetic reconstruction using within-species concatenated bracoviral orthologs shows great congruence with previously reconstructed insect species phylogenies. Our findings suggest that bracoviruses present in Diptera originate from a single integration event of the viral genome that occurred in an ancestor insect before the evolutionary radiation of different insect orders.
Highlights
Mutualism between eukaryotes and viruses is rare, since most viruses have parasitic associations with their hosts [1–3]
Our findings suggest that bracoviruses present in Diptera originate from a single integration event of the viral genome that occurred in an ancestor insect before the evolutionary radiation of different insect orders
We aimed to identify polydnaviruses (PDVs) present in five recently sequenced tsetse fly genomes (G. austeni, G. brevipalpis, G. fuscipes, G. m. morsitans, and G. pallidipes) and the housefly (Musca domestica) [16, 25], by using references described in three parasitoid wasps (Cotesia sesamiae Mombasa bracovirus, Cotesia congregata, and Glyptapanteles flavicoxis) [26]
Summary
Mutualism between eukaryotes and viruses is rare, since most viruses have parasitic associations with their hosts [1–3]. A group of double-stranded DNA (dsDNA) viruses called polydnaviruses (PDVs) have symbiotic associations with thousands of parasitoid wasps (order Hymenoptera), which parasitize immunocompetent lepidopteran larvae to enable successful reproduction [4]. PDVs have co-evolved with wasps and present a unique opportunity to investigate genome rearrangements associated with these unique mutual symbiotic relationships [2, 5]. Bracoviruses are common within a monophyletic group of wasps known as the Microgastroid complex [8]. It is thought that bracoviruses evolved from integration of a nudivirus into the genome of a Microgastroid complex ancestor approximately 100 million years ago (mya) [9]. Mutualism between wasps and bracoviruses developed over time, and functional association is estimated to date back to around 73.7 ± 10 mya [10]. Bracoviruses exist in two forms: a linear provirus integrated into the host genome that mediates vertical transmission as Mendelian traits, and as circular dsDNA virions [11, 12]. Particle production and packaging into virions occur exclusively in a specialized part of the wasp ovaries (the calyx) [12], and precede injection alongside one or more
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