Incidence and Diversity of TorixRickettsia-Odonata Symbioses

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 'Wolbachiapandemic', recent work has emphasised the importance of other microbial symbionts. In this study, we present a survey of odonates (dragonflies and damselflies) for torix groupRickettsia, 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 withRickettsia. 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 torixRickettsia. Analysis ofRickettsiagene 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 coinfectingRickettsiastrains in two species. FISH analysis indicatedRickettsiawere observed in the ovarioles, consistent with heritable symbiosis. We conclude that torixRickettsiarepresent 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.

Automated summary

The study reveals the presence of diverse Rickettsia symbionts in odonates, with the establishment of some symbiotic relationships likely through mitochondrial introgression between sister species. FISH analysis indicates the presence of Rickettsia in ovarioles, consistent with the characteristics of heritable symbionts.