Wolbachia strain diversity in a complex group of sympatric cryptic parasitoid species

Abstract

Abstract Background Maternally-inherited symbionts can induce pre-mating and/or post-mating reproductive isolation between sympatric host lineages, and speciation by modifying host reproductive phenotypes. The large parasitoid wasp genus Cotesia (Braconidae) includes a diversity of cryptic species, each specialized in parasitizing one to few related Lepidoptera host species. Here, we characterized the infection status of an assemblage of 21 Cotesia species by several microbial symbionts, as a step towards testing whether symbionts might provide a barrier to gene flow between the parasitoid host lineages. Results The symbiotic microbes Arsenophonus, Cardinium, Microsporidium and Spiroplasma were not detected in the Cotesia wasps. However, the endosymbiotic bacterium Wolbachia was present in at least eight Cotesia species. Some of the closely related Cotesia species carry similar Wolbachia strains, but most Wolbachia strains showed patterns of horizontal transfer between phylogenetically distant host lineages. Conclusions Consequently, we did not detect co-phylogenetic signals, suggesting Wolbachia is not a strictly obligatory beneficial symbiont in these insects. Instead, as a potential facultative symbiont of Cotesia species, Wolbachia may still function as a key-player in the biology of the parasitoid wasps, but its role in the evolution of this complex clade of cryptic species remains to be further investigated.