Could Genetic Engineering Save the Galápagos?
Invasive species have been a problem in the Galápagos Islands since mariners first arrived there. Hundreds of introduced species of plants, insects, reptiles, birds and mammals live in the archipelago, displacing and in some cases preying on native species.
Eradicating invasive species can be a brutal job. On the island of Floreana, a plan to eliminate the rodents that raid the nests of native birds and reptiles calls for 400 tons of rat poison, requiring weeks of dislocation for pets, livestock and perhaps children.
Genetic manipulation—for example, tweaking sex inheritance in rodents to produce an all-male, and thus reproductively doomed, population—is being discussed as a safer alternative to poison and bullets. But what are the risks? And would it even work?
On September 25, 1835, during the HMS Beagle’s sojourn to the Galápagos archipelago, Charles Darwin first set foot on what was then known as Charles Island. He found a colony of 200 to 300 inhabitants, nearly all political exiles sent there by Ecuador, aka the “Republic of the Equator,” after a failed coup attempt. The lowlands did not much impress Darwin, with their “leafless thickets,” but after trudging four miles inland and upward to a small, impoverished settlement in the highlands, he found “a green and thriving vegetation,” cultivated with bananas and sweet potatoes, along with a group of islanders who, “although complaining of poverty, obtain, without much trouble, the means of subsistence.” That was mainly because of the tens of thousands of giant tortoises that once prowled these islands. “In the woods,” Darwin noted, almost as an afterthought, “there are many wild pigs and goats.”
On the morning of August 25, 2017, Karl Campbell bounded off a twin-engine motorboat and onto the dock of that same humble island. Now known as Floreana, the island has 144 residents, half as many as in Darwin’s time, and Campbell seemed to know them all. Dressed down in a baseball cap, blue jeans and gray T-shirt that read “Island Conservation,” he ambled up to Claudio Cruz, at the wheel of a local bus (a converted truck with benches in the back), and exchanged some banter. He waved hello to Juanita and Joselito, who manned the Ecuadorian government’s biosecurity checkpoint on the dock. He shouted out another “Hola” to the postmaster, popped his head into the community center to greet Myra and Holger, a farmer, and paused to catch up with Carmen, the woman who monitors the public bathrooms near the landing. His path up Floreana’s one paved road was interrupted by salutations, chitchat, short jokes and the one-cheek kisses that are the custom in Ecuador.
Campbell, a 42-year-old Australian who has lived in the Galápagos Islands for 20 years, is a gregarious and outgoing fellow, with a tendency to begin conversations with “All good, mate?” But the cheery demeanor and bonhomie he displayed that morning is an essential part of a massive scientific undertaking. Campbell has a Ph.D. in vertebrate pest management from the University of Queensland in Australia, and in 2006 he began working as an animal removal specialist for Island Conservation, an organization based in Santa Cruz, Calif., that is devoted to preserving biodiversity and preventing extinctions by removing invasive species from islands throughout the world. Campbell has been working on eradications in the Galápagos since 1997, including a 2006 campaign to remove all the feral goats and donkeys from Floreana. A decade later he’s a project manager with Island Conservation, and the most ambitious project on its agenda is once again on Floreana: to eradicate every single rat and mouse on the island.
There are hundreds of thousands of islands in the world. “You can’t work on all of them,” Campbell says. Conservationists, according to Campbell, “are currently able to do 10 to 20 islands a year to rid them of mice. So which are the ones you should be working on most urgently? We basically draw up a list of places where we should be working to prevent extinctions.” Topping that list, he says, is Floreana.
“Floreana has one of the highest endemicity rates in the Galápagos, the highest rate of extinctions due to the invasive species here and the highest rate—by far—of critically endangered species, which makes it one of the highest-priority targets not just in the Galápagos but in the world,” Campbell says, in a spiel that has the polish and urgency of countless recitations to funders, journalists and probably every one of Floreana’s residents.
Floreana is at the limit of feasible projects using current eradication tools. The island is large (17,253 hectares, or about 46,600 acres), and it is inhabited, which complicates the task enormously. It means having to explain the logistics and consequences of the entire project—not least of which is a plan to dump 400 tons of rodent poison all over the island. That is why, since 2012, Campbell and his colleagues, such as Carolina Torres and Gloria Salvador, have been visiting Floreana almost once a month, enduring the bumpy two-hour boat ride from the main island of Santa Cruz to meet with residents, describe their proposed project, and figure out the massively complicated steps needed to protect adults, children, livestock, water and endangered species from the effects of the poison.
Such eradications require almost military-scale logistics and precision, which is why Campbell has been desperately seeking an alternative to the blunt-force tools of current techniques. One of the most appealing, to his mind, is a controversial new form of genetic manipulation known as gene drive. Compared with the frustrations he endures every day on the Floreana project, he likens the technology to a magic wand out of Harry Potter.
The basic strategy of using gene drive in the conservation setting would be to tinker with the DNA of mice, using either the new gene-editing tool CRISPR or other tools of genetic manipulation, in such a way as to tilt the odds of sex inheritance; one example would be to produce offspring that would be exclusively male, eventually producing a daughterless population of mice. The elimination of females, of course, would create a reproductive dead end for that invasive species. Gene drive is far from a practical technology at this point, but Island Conservation has been working with molecular biologists in the U.S. and Australia to create these genetically modified mice, and Campbell has made no secret of his enthusiasm for the approach at recent scientific meetings.
And that, in turn, may be why the National Academies of Sciences, Engineering, and Medicine, in a 2016 analysis on the potential benefits and risks of gene drive, included the example of daughterless mice among a series of potential scenarios where the technology might be applied. As the report noted, “Perspectives on the place of human beings in eco-systems and their larger relationship to nature—and their impact on and manipulation of ecosystems—have an important role in the emerging debate about gene drives.” That debate, in a sense, has already begun on Floreana, where residents have been weighing the benefits and risks of a massive, albeit nongenetic manipulation of their precious ecosystem for the past five years.
Source : https://www.scientificamerican.com