The Galapagos Islands are famous for exotic birds, tortoises, and iguanas, but recently the archipelago had become overrun with more prosaic animals: rats and mice. Rodents that came on old sailing ships. Rodents that stowed away on modern cruises. Wherever they came from, rodents that eat the eggs and chicks and hatchlings of the animals that so dazzled Charles Darwin.
The same story plays out on islands all over the world. So Island Conservation, a nonprofit that rids islands of invasive species, has come up with a daring plan: genetically engineer the rodents so that they all turn into males, shrinking the population one lonely pest at a time.
This plan is far from going into effect, but it gets a serious airing in a report out today from the National Academy of Sciences, a prestigious group that often makes recommendations on controversial areas of research. The make-all-rodents-boys idea is one of seven case studies for the use of “gene drives”—engineered pieces of DNA that spread more quickly through a wild population than any normal gene would. You might say gene drives are a way to cheat evolution. Gene drives could also be dangerous and unpredictable; once a manmade DNA sequence gets into a wild population, it’s hard to get back out again. The National Academy’s report lays out guidelines for scientists to responsibly study this method of genetically altering wild plants and animals.
Gene drives have gotten a lot of attention as a way to prevent mosquitoes from spreading disease:
Scientists have engineered mosquitoes with gene drives that kill the parasite behind malaria, and they’re working on gene drives that either eradicate the mosquitoes that spread dengue, chikungunya, and Zika or make them resistant to the viruses. The recent rise of Crispr gene-editing technology has made it easier than ever for scientists to construct gene drives.
But using gene drives not to benefit humans but to restore natural habitats—like tropical islands beset with invasive rats—forces you to answer a very basic question: What is natural? What does it mean to engineer animals to restore nature? Environmentalists have long decried genetically modified organisms, but will they embrace them for conservation?
Kent Redford, former director of the Wildlife Conservation Society Institute, has questioned the working definition of “natural,” and in 2013 he wrote about the lack of dialogue between synthetic biologists and conservationists. The reaction among conservationists he says, was “a range of anger and disgust to enthusiasm and excitement.” Since then Redford, along with Ryan Phelan, executive director of Revive and Restore—an organization that promotes synthetic biology for the “genetic rescue” of endangered and extinct species—have held meetings to get the two groups talking about specific problems, like invasive rodents on islands.
No matter how you feel about genetic modification, the current approach to killing island invasives might make you understand the “enthusiasm” for gene drives.
It is not pretty. Recently, on the British island of South Georgia, pilots spread 200 tons of bait one helicopter load at a time, blanketing the island in a rat poison called brodifacoum. Brodifacoum keeps blood from clotting, so the rodents die of internal bleeding—as can birds and other mammals at high enough doses. But gene drives? “We could do it in the most humane way possible by having them just turn to an all-male population and live out their natural lives,” says Heath Packard, communications director for Island Conservation.
Islands are also well suited for gene drive solutions because the ocean is a natural barrier against their spread. And invasive rodents are a critical problem: As Darwin discovered, islands are hotbeds of biodiversity, and 40 percent of the critically endangered species in the world live on islands. Plus rats and mice are an easy genetic target because scientists have long tinkered with their genetics in the lab. The downside, of course, are unintended consequences. Ecology is complicated, and nobody has put a gene out in the wild before.
Island Conservation’s scientists were investigating gene drives as a possible “game-changing” eradication technology even before Crispr became hot. Their research partners at Texas A&M University and North Carolina State University are studying a naturally-occurring gene drive in mice that doesn’t even require Crispr technology. Island Conservation has also partnered with the US Department of Agriculture and Australia’s national Commonwealth Scientific and Industrial Research Organisation so when the time comes, it gets regulatory approval for field tests in the future. That’s all years away, says Packard, though the group is now planning to fundraise for the gene drive research.
The National Academy report considers other conservation scenarios for gene drives: killing off mosquitoes that spread avian malaria in Hawaii and controlling invasive knapweeds in US forests. But reading the report, you get a sense that the scientists realize they are out of their depth. “Questions about how to define ‘nature’ and how to understand the value attached to nature raise a number of difficult philosophical and social problems,” says the report. “They are left here as open questions, and are part of a growing and heated debate among environmentalists about the values that underpin environmentalism.” Consider this: Gene drives may be “unnatural,” but how natural is dropping tons of rat poison out of the sky?
In any case, if scientists can construct such a gene drive, if conservationists can get permission to release mice carrying them, and if everything goes as planned, then islands like the Galapagos stand to benefit. A huge rat poisoning campaign from 2007 to 2014 rid the Galapagos of most of its pests, but with so much boat traffic there, rodents could make their way to the islands again. Where Darwin first made the observations that led him to understand the laws of evolution, scientists could use the technology that will try to cheat the game.