Wolbachia endosymbionts distort DNA barcoding in the parasitoid wasp genus Diplazon (Hymenoptera: Ichneumonidae)

Molecular species delimitation has the potential to speed up both discovery and description rates for new species. However, several studies have shown a limited performance of the standard DNA barcoding approach which relies on a single mitochondrial gene, cytochrome oxidase 1 (COI). Besides incomplete lineage sorting or a low substitution rate, distortion of mitochondrial inheritance patterns by bacterial endosymbionts could explain the failure of barcoding. Numerous reviews have discussed this phenomenon, but only few empirical examples exist. In the present study, we examine the effect of Wolbachia bacteria on barcoding in the parasitoid wasp genus Diplazon. Although integrative taxonomy recognizes 16 species, COI only recovers up to ten. Adding multivariate morphometrics, genotyping a fast-evolving nuclear gene (ITS2) and screening the Diplazon species for Wolbachia, we show that the failure of DNA barcoding coincides with the presence of the endosymbiont. Two species even share identical COI haplotypes and Wolbachia strains, even though ITS2 suggests that they are not closely related. This is one of very few examples of mitochondrial DNA introgression between well-established insect species, facilitated by Wolbachia. We review similar reports, provide a list of criteria to identify endosymbiont-mediated introgression, and discuss the prevalence and impact of this phenomenon on insect systematics and evolution