Wasps stole genes from viruses

PEOPLE DOMESTICATED sheep and cattle, wheat and maize. Wasps domesticated viruses. And, just as domesticating other species helped human populations explode, so viral domestication assisted an explosion of wasps. That, at least, is the conclusion of Benjamin Guinet, an evolutionary biologist at Lyon University, in France. As he writes in the , he thinks an ancestor of a group of wasps called the Cynipoidea, which parasitise flies, corralled 18 viral genes into its genome in an act of domestication that happened 75m years ago, and that this helped the group flourish.The nest-dwelling, picnic-disrupting black-and-yellow terrors that generally come to mind when the word “wasp” is mentioned are actually unrepresentative of the group. Most wasps are small, solitary and reproduce by laying their eggs in or on other arthropods, particularly insects and spiders. Cynipoidea specialise on fly larvae. As with other parasitoid wasps, when their eggs hatch, the hatchling grubs then eat their hosts alive.To assist their offspring in this endeavour, mother Cynipoidea wasps also squirt into the flies a mix of venom, viruses and other materials that sabotage the host’s immune system. Some of this material consists of proteins that look remarkably like ones which viruses themselves produce to attack other organisms.These virus-like proteins are, nevertheless, encoded not in viral genes but in genes which are now part of the wasps’ genomes. Dr Guinet therefore presumed that ancestral cynipoids had swiped them from viruses at various times in the past. He wondered when. To find out, he and his colleagues analysed the genomes of 41 Cynipoidea wasps from six subfamilies using molecular-clock techniques that estimate how fast genes in different lineages have diverged from each other. That let them work out when each gene had arrived in the ancestral genome.The answer was the same for all 18. So it seems that the domestication of these genes was a single event. Intriguingly, this corresponds to the moment in the Cretaceous period when the group of flies that cynipoids parasitise began itself to diversify. Dr Guinet reckons that viral domestication helped facilitate the wasps’ diversification in response to the multiplication of the number of host species.