Scientists are lab-testing a death fish that will wipe out its own species. Pests across the planet beware.
The dirt road that snakes up into the Tasmanian highlands is rutted from generations of Australian anglers who trekked to the shores of what was once a vast crystalline lake. But today, there's not a soul in sight. I park my rented Hyundai and go walkabout. The only sound is the wind through the lake's desiccated marshes, wetlands that used to echo with the splash of platypus and the chatter of native birds and frogs. The silence is broken by a pickup truck rattling down the road toward me. "You all right, mate?" asks the driver, surprised to see anyone at Lake Crescent. I nod. I haven't come to fish but to witness the ecological devastation wrought by an alien invasion.
The aliens in question: European carp. Wildlife officials discovered them swimming among the lake's rare native fish seven years ago and wasted no time taking drastic action by quarantining the area. Opportunistic and adaptable, Cyrprinus carpio uproots aquatic vegetation and turns clear-running water into a muddy morass, depriving native fish of food, light, and oxygen. To save Lake Crescent, government authorities had to partially destroy it by lowering water levels, denying the carp space to spawn. The invader — likely the descendant of juveniles used as fishing bait — has been held in check but are not yet eradicated.
The planet's most farmed fish and a staple of Asian diets, carp are the Borg of the fish world, infiltrating lakes and rivers from China to California. In Australia, they are reviled for the environmental destruction caused by their prolific breeding. The so-called river rabbits have come to dominate the country's waterways since they were released into the wild a century ago.
Now, for the first time anywhere, Australian scientists have a plan to genetically engineer carp out of existence. Injected with "daughterless" genes, the fish will produce only male offspring and thus spawn the seeds of their own destruction. As these doomsday carp mate with their wild cousins, the population of each targeted river or lake will eventually drive itself to extinction.
First, though, there are smaller fish to fry. Two hours south of Lake Crescent is the government's marine research center in Hobart, the capital of the island state of Tasmania. Biologist Ron Thresher ushers me into a nondescript laboratory. When he raps the lab's thick, tinted windows, there's a distinctive thud. "Bulletproof," he says. The floors, I notice, slope downward. "Every drop of water that comes out of here gets sterilized." These safeguards keep outsiders from absconding with genetically engineered fish and prevent tainted water from escaping the lab.
The subject of all this security is darting about a tank lining one wall of an inner chamber: the 2-inch-long zebra fish, an unexceptional aquarium dweller procured from a local pet store — except that some of these translucent striped fish carry prototypes of the daughterless gene in their gonads. If all goes well, construction of the daughterless carp will begin within two years.
INVASIVE SPECIES COST BILLIONS IN THE US ALONE. THE CURE: "DAUGHTERLESS" GENES.
Genetic engineering offers a solution to the feral peril that has plagued the region since Captain Cook released a pair of pigs in Tasmania in 1777. As Thresher tinkers with fish genes, researchers on the mainland are studying ways to sterilize foxes and other foreign mammals. With dozens of indigenous animals teetering on the brink of oblivion, scientists are racing the clock for a tech fix to the problem of invasive species, which threatens biodiversity worldwide and costs the US alone more than $138 billion a year. But will the cure be worse than the disease?
When the British First Fleet sailed into Sydney Cove on January 26, 1788, its cargo of convicts encountered a fantastical landscape. Oddly angled trees shed not their leaves but their bark, while furred animals of strange proportions hopped, burrowed, and laid eggs. The colonists set out to remake the Australian bush into a facsimile of the English countryside, populating the land with rabbits, goats, and other familiar creatures they'd brought from home. To complete the pastoral tableau, the local gentry imported the red fox so that the antipodean woodlands would echo with the braying of hounds on the hunt.
The result was a marsupial massacre. With few competitors, the fox and feral cat ate their way across the continent, finding the pouched natives to be easy prey. Goats and rabbits, meanwhile, denuded the terrain of food and shelter. The invasion has contributed to Australia's appalling extinction rate — at least 18 native mammal species have been lost since European settlement, more than in any other country.
The reach of the fox and its fellow transplants is stunning. I've spotted foxes on remote west coast beaches waiting for green sea turtles to come ashore. Wild camels have towered over my Toyota in the central desert, and I've stumbled across the muddy wallows of feral pigs in primeval rain forests of the tropical north.
Australians have been battling nonnative pests with mixed success since colonial days. Just 30 years after unleashing the fox, the government put a bounty on its head. In the 20th century, government scientists bombarded foxes with poisoned kangaroo meat and released a virus deadly to Aussie rabbits.
Fixing one feral problem often triggers another. When foxes were eradicated from a west coast peninsula two years ago, the cat population soared. Some of Australia's most intractable nonnative species are those deliberately let loose to control another pest. In 1935, the government imported cane toads, thinking the amphibian would eat a beetle that was blighting the sugar cane crop. The cane toad ate everything but. Spreading through Australia like a biblical plague, the toad, which secretes a deadly poison, devastated native wildlife.
The diminutive Central American mosquito fish — introduced to control winged bloodsuckers — has become the cane toad of the waterways, eating the eggs of Australia's fish but showing scant interest in mosquito larvae. After the zebra fish, the mosquito fish is next up for the daughterless treatment. And then there are the carp, which have decimated habitats and dominated native fish in the race for food. In the country's largest river system, the Murray-Darling Basin in southeast Australia, carp now constitute 90 percent of the fish biomass. "There are between 30 and 40 native species in the river. About half of them are at lower levels with some threat of extinction," says Kevin Goss, an executive with the Murray-Darling Basin Commission.
If anything, aquatic invaders have proven even more difficult to eradicate than foxes. You can't poison carp without putting native fish at risk. The answer: Program the carp to self-destruct.
Separated from mainland Australia by 150 miles of ocean that rose after the last Ice Age, the Ohio-sized island of Tasmania was once the end of the world. It was home to Australia's most feared penal colony, whose overlords were obsessed with keeping the British Empire's worst convicts from escaping. Today, preserving Tasmania's abundant biodiversity means holding the outside world at bay. Luck and distance kept Tasmania largely free of destructive species in the 19th century. Today, ecological disaster is just a ferry ride away.
As I drive down a deserted highway, logging trucks rumble by, and the Twin Peaks soundtrack plays in my head. The thickly forested landscape conjures up images from Richard Flanagan's Gould's Book of Fish, a phantasmagoric account of a barbarous 19th-century Tasmanian penal settlement on "an island in the middle of a wilderness far off the coast of a nowhere land so blighted it existed only as a gaol." I find myself imagining mad scientists reanimating mutant fish on the expanses of Tasmania's still-unexplored wild lands.
It's a bit of a letdown, then, to meet Ron Thresher, a laid-back 53-year-old American immigrant. Dressed in jeans, sweater, and boots, the lanky fish biologist looks as if he would be just as at home in Boulder or Santa Cruz as at the marine lab on the Hobart waterfront, operated by the government's Commonwealth Scientific & Industrial Research Organization. The New York native came to Australia in 1979 on a postdoc. About eight years ago, Thresher joined a CSIRO division established to control marine pests. As global trade intensified in the 1990s, so did the number of unwanted overseas visitors hitching rides to Australia in ballast water. But by then the idea of introducing a supposedly benign foreign species to control a destructive one had become anathema. Rapid advances in genetics pointed to a new approach. Thresher's team spent several years modeling different population-busting scenarios before they had their eureka moment. Biologists have long known that female fish develop when an enzyme called aromatase transforms androgen into estrogen. It's been possible to chemically block aromatase to produce only males. "Where we were clever is that we figured out a way to make it an inheritable characteristic," Thresher says.
To prove the concept, the scientists concocted a daughterless gene for the zebra fish, a cousin of the carp. First they located the gene that produces aromatase. Then they sequenced that gene in reverse — creating a blocker that binds to and neutralizes the aromatase gene. Thresher tested the new gene by injecting it into zebra fish eggs. The result: Eighty percent of the brood was born male — a striking success given that some of the daughterless genes are inevitably destroyed during the injection process. The Murray-Darling Basin Commission subsequently enlisted Thresher to develop a daughterless carp.
Phase two, now under way, is the creation of a daughterless mosquito fish. A handful of the 1½-inch-long drab but destructive species are swimming around a small tank in Thresher's lab. The fast-breeding fish — they become sexually mature at two weeks — will allow Thresher's team to evaluate how (and if) the daughterless gene spreads through the population generation after generation. That'll give Thresher the chance to work out any kinks before constructing a daughterless gene for the carp, which takes two years to reach reproductive age. Three years of mosquito fish lab trials will be followed by field tests in high-security ponds on the mainland. If all goes well, genetically modified mosquito fish will be released to eradicate a targeted fish population.
NIGHTMARE SCENARIO: THE CARP ESCAPE AND CROSSBREED — OR EVOLVE INTO SUPERPESTS.
The mosquito fish trials will help resolve the many unknowns about releasing these terminator animals into nature. How many daughterless genes should the carp carry? Just how many doomsday carp — and how long — will it take to eliminate a wild population? Will the daughterless genes "jump" to other species?
The answers will be supplied in part by a computer model — called Carpmod — that will simulate the Murray-Darling Basin. "You have an underlying series of equations that represent how fish move from one area to another," explains CSIRO ecosystem modeler Nic Bax. "Given that, you can release the daughterless carp, see how they're going to breed with fish that are there, and observe in the model how they spread." The model will first look at daughterless mosquito fish. As the fish move from lab to pond to lake, the program will be continually refined as its predictions are tested in the field.
Aussie environmentalists are skeptical that a computer can replicate wild Australia. "We're all too aware that things don't always end up operating in nature the way they do in a laboratory experiment," cautions Bob Phelps, director of the Australian Gene Ethics Network. "To talk about the release of millions of genetically engineered fish into complex ecological systems and know what the upshot will be is impossible." The nightmare scenario: Daughterless carp somehow escape to other parts of the world and breed with dozens of closely related species. Or they evolve in unforeseen ways into superpests.
For the moment, the carp project is attracting little attention from Australian enviros. Expect a bigger fight from American greens if the technology is exported across the Pacific. "Sierra Club has called for a moratorium on all releases of genetically engineered organisms," says Sierra Club activist Laurel Hopwood, who is fighting to keep genetically altered salmon off American dinner plates.
Thresher insists the daughterless carp will not be a frankenfish. "When we build this for carp, it will be from 100 percent carp genes. We'll just be rearranging them to achieve what we want." He anticipates the next question. "'Omigod, what if someone sneaks one of these carp to Europe? Are you going to endanger the species globally?' The short answer is no. If someone snuck a thousand of these things to Europe and released them into the Danube, it really wouldn't make a significant impact," he says.
He figures the math will work this way: To eliminate carp from a river, you need to introduce daughterless carp at a rate equal to between 0.5 percent and 1 percent of the total population each year for 20 years. So a lake with 100,000 wild carp would need to be stocked with 500 to 1,000 daughterless carp annually. Presumably, you could speed up the process by introducing additional modified carp. "If three years into the exercise we suddenly find the thing has jumped to Australian bass, we can stop stocking it. And the gene will eventually be overwhelmed by the wild type," he says. "There is plenty of time to launch a counter-gene." It would take two decades to wipe out the carp. Or maybe longer. Anne Kapuscinski, a University of Minnesota geneticist and a leading expert on transgenic fish, suspects the complex dynamics of fish populations and genetics may resist a daughterless assault. Nature could conspire to give the carp a higher survival rate or simply turn off the daughterless gene.
Globalization means no island is an island anymore. As Thresher and I talk carp, foxes — smuggled in from the mainland — are roaming the Tasmanian bush and may be establishing a beachhead. "If foxes aren't eradicated soon, we'll have a drumroll of extinctions," warns wildlife officer Nick Mooney. Australian government scientists are working on a noncontagious virus that will carry a DNA sequence designed to sterilize foxes. A similar but contagious immunocontraceptive technique is being tested on Aussie rabbits.
With destructive alien species expanding worldwide, such genetic technology is likely to spread like, well, carp. The insatiable northern snakehead fish — a native of China that can breathe air and walk on land — has been multiplying in a Maryland pond. The Great Lakes have been invaded by more aliens than those in a Star Wars bar scene. If zebra mussels and round gobies weren't wreaking havoc enough, Charles Krueger, science director of the Great Lakes Fishery Commission, now has to contend with the big head carp, a 50-pound monster from China. "We are certainly interested in daughterless gene technology," says Krueger. "Our primary concern is if somehow that technology got back to the species' native distribution."
It will probably be seven more years before the doomsday carp is ready to swim wild. But ask Ron Thresher about the future of the daughterless gene, and he rattles off a list of possible candidates: snails, cane toads, birds maybe. And foxes? "In theory, it could work on mammals, although you would have to use different genes. Sexual development in mammals is much, much, much more complicated than in fish." He pauses. "It may well work on something like cats and foxes. I'd be quite keen to pursue that." With the tools of genetic manipulation in his grasp, it's only a matter of carpe diem.
