The missing link to viral symbiogenesis: Genomic clues from a young parasitoid-virus mutualism

A central question regarding insect-microbe symbiosis concerns the biological mechanisms that lead to its formation. Bacterial symbionts constitute the bulk of current research in the field, although symbiotic viruses have also been shown to play pivotal roles in insect biology. The evolution of beneficial viruses has repeatedly occurred within the parasitoid wasps, in which viruses are used by wasps as biological weapons to exploit host insects. While most examples of this phenomenon represent ancient, endogenous viruses that are permanent components of wasp genomes, the wasp Diachasmimorpha longicaudata maintains a mutualistic relationship with an exogenous poxvirus, known as Diachasmimorpha longicaudata entomopoxvirus (DlEPV). We recently identified the presence of two cryptic species of D. longicaudata from wild wasp collections on Hawaii Island, only one of which is stably infected with DlEPV. These results suggest that the D. longicaudata- DlEPV symbiosis is extremely young and raise important questions regarding the evolutionary changes that occur within an insect and a virus to facilitate their joining into a heritable, mutualistic relationship. To continue disentangling this nascent symbiosis, we sequenced and investigated the genomes of both D. longicaudata species complex members, along with the genomes of DlEPV strains obtained from laboratory colonies and various locations on Hawaii Island. We found intriguing genetic differences at the nucleotide and gene levels among viral strains, which may translate to functional differences in the interactions between DlEPV, D. longicaudata wasps, and their fruit fly hosts. Our findings therefore provide a new genomics-scale glimpse into the early stages of viral symbiogenesis.