Host–endoparasitoid–endosymbiont relationships: concealed Strepsiptera provide new twist toWolbachiain Australian tephritid fruit flies

Abstract

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 wholegenome 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 parasitization. We performed the first genetic characterization of D. daci and detected D. daci in Wolbachia-positive flies not visibly parasitized, and most but not all Wolbachia-negative flies were D. daci-negative, presumably reflecting polymorphism for the Wolbachia infections in D. daci. We dissected D. daci from stylopized flies and confirmed that Wolbachia infects D. daci, but also found Wolbachia in stylopized 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 parasitization 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.

Substantial rearrangements, single nucleotide frameshift deletion and low diversity in mitogenome of Wolbachia-infected strepsipteran endoparasitoid in comparison to its tephritid hosts

“…Phylogenetic analyses of the D. daci mitochondrial cox1 , nad1 , 16S rRNA and nuclear 18S rRNA genes revealed that it belongs to the family Halictophagidae 47 , confirming earlier morphological analyses which placed it into the halictophagid subfamily Dipterophaginae 33 , 37 . The WGS analyses and further diagnostic testing of both parasitised and unparasitised tephritid fruit fly individuals revealed a clear link between D. daci and two Wolbachia strain sequence types, ST-285 and ST-289, previously detected in these tephritid fruit fly samples at low prevalence 48 , 49 ; this demonstrated that D. daci is the true host of these two strains, w Ddac1 and w Ddac2, which occur at a high prevalence in D. daci 47 . Furthermore, no Wolbachia genes known to cause host reproductive manipulations were found, and there was a low diversity in the mitochondrial PCGs of D. daci when compared with its nuclear 18S rRNA gene sequences 47 .…”

“…The WGS analyses and further diagnostic testing of both parasitised and unparasitised tephritid fruit fly individuals revealed a clear link between D. daci and two Wolbachia strain sequence types, ST-285 and ST-289, previously detected in these tephritid fruit fly samples at low prevalence 48 , 49 ; this demonstrated that D. daci is the true host of these two strains, w Ddac1 and w Ddac2, which occur at a high prevalence in D. daci 47 . Furthermore, no Wolbachia genes known to cause host reproductive manipulations were found, and there was a low diversity in the mitochondrial PCGs of D. daci when compared with its nuclear 18S rRNA gene sequences 47 . This suggests that due to its maternal coinheritance with mitochondria, Wolbachia may have reduced mitochondrial diversity as a consequence of a positive fitness effect on D. daci .…”

“…Dipterophagus daci is the only described strepsipteran parasitising Diptera (except for undescribed strepsipteran species from Papua New Guinean platystomatid flies) and has been recorded in 22 dacine fruit fly species (Tephritidae: Dacini) in Australia and the Solomon Islands 45 – 47 . Recent molecular analyses of whole genome sequencing (WGS) libraries of field-collected adult tephritid fruit flies from Australia detected genomic sequences of D. daci , including its entire mitogenome, indicative of concealed parasitisation of the sequenced flies 47 .…”

“…Dipterophagus daci is the only described strepsipteran parasitising Diptera (except for undescribed strepsipteran species from Papua New Guinean platystomatid flies) and has been recorded in 22 dacine fruit fly species (Tephritidae: Dacini) in Australia and the Solomon Islands 45 – 47 . Recent molecular analyses of whole genome sequencing (WGS) libraries of field-collected adult tephritid fruit flies from Australia detected genomic sequences of D. daci , including its entire mitogenome, indicative of concealed parasitisation of the sequenced flies 47 . Phylogenetic analyses of the D. daci mitochondrial cox1 , nad1 , 16S rRNA and nuclear 18S rRNA genes revealed that it belongs to the family Halictophagidae 47 , confirming earlier morphological analyses which placed it into the halictophagid subfamily Dipterophaginae 33 , 37 .…”

“…Recent molecular analyses of whole genome sequencing (WGS) libraries of field-collected adult tephritid fruit flies from Australia detected genomic sequences of D. daci , including its entire mitogenome, indicative of concealed parasitisation of the sequenced flies 47 . Phylogenetic analyses of the D. daci mitochondrial cox1 , nad1 , 16S rRNA and nuclear 18S rRNA genes revealed that it belongs to the family Halictophagidae 47 , confirming earlier morphological analyses which placed it into the halictophagid subfamily Dipterophaginae 33 , 37 . The WGS analyses and further diagnostic testing of both parasitised and unparasitised tephritid fruit fly individuals revealed a clear link between D. daci and two Wolbachia strain sequence types, ST-285 and ST-289, previously detected in these tephritid fruit fly samples at low prevalence 48 , 49 ; this demonstrated that D. daci is the true host of these two strains, w Ddac1 and w Ddac2, which occur at a high prevalence in D. daci 47 .…”