This is how Darwin says evolution works: Random mutations occur within an organism’s genetic code. When they help the organism survive long enough to reproduce, they are passed on to the next generation.
Yet this is how butterflies and moths have evolved: They did it Darwin’s way. But some also show evidence of mutation that isn’t random but intentional—only not intentional by them.
New research by a team of French scientists reporting in the September 17 issue of PLOS Genetics shows that many butterflies and moths have acquired genes from parasitic wasps in what they call an inter-species Horizontal Gene Transfer. The wasps inject their eggs into caterpillars for incubation. When they do they also inject a large virus, the bracovirus. Because, over the last 100 million years, bracoviruses and parasitic wasps have existed symbiotically, the wasp genome now fully incorporates that of the virus. On a genetic level they “look like” each other.
Once inside the caterpillar, the bracovirus mixes its DNA with that of the caterpillar. Genetic mixing is what all viruses do to hosts. In this case, though, the intention is not the usual one—to use the host cells as virus production factories. Rather the genetic mixing fools the caterpillar’s immune system into accepting the virus—and the egg—as parts of its own body. As the egg matures it cannibalizes the caterpillar. But apparently not all of the caterpillars have died, for the French team has discovered parasitic wasp genes in the genomes of many adult butterflies and moths. The scientists believe that the survival benefit the virus confers is that its presence protects against baculovirus, which commonly infects butterflies and moths.
This is a story of natural, trans-species evolution. But because it’s also one of natural genetic modification, at first blush it seems to provide a counterargument to people who decry GMO advances as perverted and who warn of the possibility of lab-created catastrophes. Still, the French research team offers a word of caution. If horizontal gene transfer has happened between parasitic wasps and butterflies, it may happen regularly in nature. If so, when lab scientists introduce genes into one species for one purpose, they should assume that some day that gene may be found unexpectedly and perhaps even disastrously in another species.
For more information: Laila Gasmi, Helene Boulain, Jeremy Gauthier, Aurelie Hua-Van, Karine Musset, Agata K. Jakubowska, Jean-Marc Aury, Anne-Nathalie Volkoff, Elisabeth Huguet, Salvador Herrero, and Jean-Michel Drezen, “Recurrent Domestication by Lepidoptera of Genes from Their Parasites Mediated by Bracoviruses,” PLOS Genetics, September 17, 2015