Wolbachia as agents of extensive mtDNA lineage sharing between species through multiple infection

Wolbachia can manipulate arthropod host reproduction, triggering the homogenisation of mtDNA variation within species and introgression between hybridising species through indirect selection. While fixation within species of mtDNA variants linked to Wolbachia infections has been documented, a broader understanding of the potential consequences of Wolbachia infection through hybridisation is limited. Here we evaluate Wolbachia transmission through hybridisation as a mechanistic explanation for extensive mtDNA paraphyly between two species of iron-clad beetle (Zopheridae). Our analyses reveal a complex pattern of mitochondrial variation, supporting the introgression of at least five mtDNA lineages from Tarphius canariensis into T. simplex, in a background of a shared Wolbachia infection across both species. Genetic clustering and demographic simulations reveal a clear pattern of nuclear differentiation between species, a limited signature of historical gene flow, and the eastwards range expansion of T. simplex across the existing distribution of T. canariensis. These results are consistent with hybridisation during early stages of secondary contact, during which Wolbachia infection facilitated recurrent mtDNA introgression events. These results highlight the complex restructuring of mitochondrial differentiation across invertebrate species that can result from bacterial endosymbiotic infections, a phenomena with potentially profound impacts for the disciplines of phylogeography and species delimitation.