Host-endoparasitoid-endosymbiont relationships: concealed Strepsiptera provide new twist to Wolbachia in Australian tephritid fruit flies

Wolbachia are widespread endosymbionts that affect arthropod reproduction and fitness. Mostly maternally inherited, Wolbachia are occasionally transferred horizontally. Previously, two Wolbachia strains were reported at low prevalence and titres across seven Australian tephritid species, possibly indicative of frequent horizontal transfer. Here, we performed whole-genome sequencing of field-caught Wolbachia-positive flies. Unexpectedly, we found complete mitogenomes of an endoparasitic strepsipteran, Dipterophagus daci, suggesting that Wolbachia in the flies are linked to concealed parasitisation. We performed the first genetic characterisation and detected D. daci in Wolbachia-positive flies not visibly parasitised, but most Wolbachia-negative flies were D. daci-negative, presumably reflecting polymorphism for the Wolbachia infections in D. daci. We dissected D. daci from stylopised flies and confirmed that Wolbachia infects D. daci, but also found Wolbachia in stylopised fly tissues, likely somatic, horizontally transferred, non-heritable infections. Furthermore, no Wolbachia cif and wmk genes were detected, and very low mitogenomic variation in D. daci across its distribution. Therefore, Wolbachia may influence host fitness without reproductive manipulation. Our study of 13 tephritid species highlights that concealed early stages of strepsipteran parasitisation led to the previous incorrect assignment of Wolbachia co-infections to tephritid species, obscuring ecological studies of this common endosymbiont and its horizontal transmission by parasitoids. This article is protected by copyright. All rights reserved