Abstract
Heritable microbes are an important component of invertebrate biology, acting both as beneficial symbionts and reproductive parasites. Whilst most previous research has focussed on the ‘Wolbachia pandemic’, recent work has emphasised the importance of other microbial symbionts. In this study, we present a survey of odonates (dragonflies and damselflies) for torix group Rickettsia, following previous research indicating that this clade can be common in other aquatic insect groups. PCR assays were used to screen a broad range of odonates from two continents and revealed 8 of 76 species tested were infected with Rickettsia. We then conducted further deeper screening of UK representatives of the Coenagrionidae damselfly family, revealing 6 of 8 UK coenagrionid species to be positive for torix Rickettsia. Analysis of Rickettsia gene sequences supported multiple establishments of symbiosis in the group. Some strains were shared between UK coenagrionid species that shared mtDNA barcodes, indicating a likely route for mitochondrial introgression between sister species. There was also evidence of coinfecting Rickettsia strains in two species. FISH analysis indicated Rickettsia were observed in the ovarioles, consistent with heritable symbiosis. We conclude that torix Rickettsia represent an important associate of odonates, being found in a broad range of species from both Europe and South America. There is evidence that coinfection can occur, vertical transmission is likely, and that symbiont movement following hybridisation may underpin the lack of ‘barcoding gap’ between well-established species pairs in the genus. Future work should establish the biological significance of the symbioses observed.
Highlights
Animals and plants commonly form associations with microbes, either by interacting with environmental microbes on their surface, in their gut, or with microbes living inside the organism’s tissues as endosymbionts
Four further Rickettsia symbioses were detected in the five additional UK species of Coenagrionidae tested in the focused screening (Table 1), resulting in a total of 6 of 8 UK coenagrionids testing positive
In cases where the individual sex was known, there was no evidence of Rickettsia infection being biased to one host sex (Table 2)
Summary
Animals and plants commonly form associations with microbes, either by interacting with environmental microbes on their surface, in their gut, or with microbes living inside the organism’s tissues as endosymbionts. The best-known example of a heritable symbiont is Wolbachia, which is estimated to infect over 50% of insect species [8]. Wolbachia can act as a nutritional symbiont for blood-feeding insects by synthesising B vitamins that the host cannot make on its own or obtain from its diet, and can enhance tolerance to RNA virus infection in diverse species [11]. This covers just a few examples of Wolbachia impacts and is not an exhaustive list
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