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March 25 - March 28, 2023
Several years ago, he and some colleagues at AAHL inserted a jellyfish gene into a hen. This gene, similar to the one I was planning to plug into my yeast, encodes a fluorescent protein. A chicken in possession of it will, as a consequence, give off an eerie glow under UV light. Next, Tizard figured out a way to insert the fluorescence gene so that it would be passed down to male offspring only. The result is a hen whose chicks can be sexed while they’re still in their shells.
“What people are not seeing is that this is already a genetically modified environment,” he went on. Invasive species alter the environment by adding entire genomes that don’t belong. Genetic engineers, by contrast, alter just a few bits of DNA here and there.
We are using our understanding of biological processes to see if we can benefit a system that is in trauma.”
The toads will eat almost anything they can fit in their oversized mouths, including mice, dog food, and other cane toads.
Within a year, they’d produced more than 1.5 million eggs. The resulting toadlets were intentionally released into the region’s rivers and ponds. It’s doubtful that the toads ever did the sugar cane much good.
Along the way, something curious happened. In the early phase of the invasion, the toads were advancing at the rate of about six miles a year. A few decades later, they were moving at twelve miles a year. By the time they hit Middle Point, they’d sped up to thirty miles a year. When researchers measured the toads at the invasion front, they found out why. The toads on the front lines had significantly longer legs than the toads back in Queensland. And this trait was heritable.
The trait that makes them truly “hated,” though, is that they’re toxic. When an adult is bitten or feels threatened, it releases a milky goo that swims with heart-stopping compounds. Dogs often suffer cane toad poisoning, the symptoms of which range from frothing at the mouth to cardiac arrest.
Australia has no poisonous toads of its own; indeed, it has no toads at all.
The list of species whose numbers have crashed due to cane toad consumption is long and varied. It includes: freshwater crocodiles, which Australians call “freshies”; yellow-spotted monitor lizards, which can grow up to five feet long; northern blue-tongued lizards, which are actually skinks; water dragons, which look like small dinosaurs; common death adders, which, as the name suggests, are venomous snakes; and king brown snakes, which are also venomous.
The Toadinator is a trap fitted out with a portable speaker that plays the cane toad’s song, which some compare to a dial tone and others to the thrum of a motor. Researchers at the University of Queensland have developed a bait that can be used to lure cane toad tadpoles to their doom. People shoot cane toads with air rifles, whack them with hammers, bash them with golf clubs, purposefully run them over with their cars, stick them in the freezer until they solidify, and spray them with a compound called HopStop, which, buyers are assured, “anesthetizes toads within seconds” and dispatches
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“I thought: Toxins are generated by metabolic pathways,” he went on. “That means enzymes, and enzymes have to have genes to encode them. Well, we have tools that can break genes. Maybe we can break the gene that leads to the toxin.”
Cane toad eggs, she discovered, had to be washed and then pierced just so, with a very fine pipette, and this had to be done quickly, before they had time to start dividing. “Refining the micro-injection technique took quite a while,” she told me.
toads can, when attacked, produce an enzyme—bufotoxin hydrolase—that amplifies the poison’s potency a hundredfold. Using CRISPR, Cooper edited a second batch of embryos to delete a section of the gene that codes for bufotoxin hydrolase.
Research on quolls suggests that the marsupials can be trained to steer clear of cane toads. Feed them toad “sausages” laced with an emetic, and they will associate toads with nausea and learn to avoid them.
Cooper thought it might be possible to fiddle with the genes that produce the gel coat on the toads’ eggs in such a way that the eggs would be impossible to fertilize.
Cooper reached a gloved hand into the tank and pulled out Blondie, whom she’d described to me as “beautiful.” He immediately peed on her.
Outlaw genes fix the game in their favor and do so in a variety of devious ways. Some interfere with the replication of a rival gene; others make extra copies of themselves, to increase their odds of being passed down; and still others manipulate the process of meiosis, by which eggs and sperm are formed.
Such rule-breaking genes are said to “drive.” Even if they confer no fitness advantage—indeed, even if they impose a fitness cost—they’re handed on more than half of the time.
Driving genes have been discovered lurking in a great many creatures, including mosquitoes, flour beetles, and lemmings, and it’s believed they could be found in a great many more, if anyone took the trouble to look for them.
In bacteria, which might be said to hold the original patent on the technology, CRISPR functions as an immune system. Bacteria that possess a “CRISPR locus” can incorporate snippets of DNA from viruses into their own genomes. They use these snippets, like mug shots, to recognize potential assailants. Then they dispatch CRISPR-associated, or Cas, enzymes, which work like tiny knives. The enzymes slice the invaders’ DNA at critical locations, thus disabling them.
Insert the CRISPR-Cas genes into an organism, and the organism can be programmed to perform the task of genetic reprogramming on itself.
If CRISPR confers the power to “rewrite the very molecules of life,” with a synthetic gene drive, that power increases exponentially. Suppose that the researchers in San Diego had released their yellow fruit flies. Assuming those flies had found mates, swarming around some campus dumpster, their offspring, too, would have been yellow. And assuming those offspring survived and also successfully mated, their progeny would, in turn, have been yellow. The trait would have continued to spread, ineluctably, from the redwood forest to the Gulf Stream waters, until yellow ruled.
Just about any gene in any plant or animal can—in principle, at least—be programmed to load the inheritance dice in its favor. This includes genes that have themselves been modified or borrowed from other species. It should be possible, for example, to engineer a drive that would spread a broken-toxin gene among cane toads. It may also be possible one day to create a drive for corals that would push a gene for heat tolerance.
While Thomas was still, in his words, “just dabbling,” he was contacted by a group that calls itself GBIRd. The acronym (pronounced “gee-bird”) stands for Genetic Biocontrol of Invasive Rodents, and the group’s ethos might be described as Dr. Moreau joins Friends of the Earth.
A suppression drive is designed to defeat natural selection entirely. Its purpose is to spread a trait so deleterious that it can wipe out a population. Researchers in Britain have already engineered a suppression drive for Anopheles gambiae mosquitoes, which carry malaria. Their goal is eventually to release such mosquitoes in Africa.
An X-shredder mouse is a mouse who’s been gene edited so that all of his X-bearing sperm are defective.
If the Anthropocene’s clearest geological marker is a spike in radioactive particles, its clearest biological marker may be a spike in rodents. Everywhere humans have settled on the planet—and even some places they’ve only visited—mice and rats have tagged along, often with ugly consequences.
In the case of New Zealand’s Big South Cape Island, ship rats didn’t arrive until the 1960s, by which point naturalists were on hand to document the results. Despite intensive efforts to save them, three species endemic to the island—one bat and two birds—disappeared.
Under the right circumstances, mice can be just as fierce as rats, and every bit as deadly. Gough Island, which lies more or less midway between Africa and South America, is home to the world’s last two thousand pairs of Tristan albatrosses. Video cameras installed on the island have recorded gangs of Mus musculus attacking albatross chicks and eating them alive.
Hundreds of uninhabited islands have been de-moused and de-ratted in this way, and such campaigns have helped bring scores of species back from the edge, including New Zealand’s Campbell Island teal, a small, flightless duck, and the Antiguan racer, a grayish lizard-eating snake.
The downside of Brodifacoum, from a rodent’s perspective, is pretty obvious: internal bleeding is a slow and painful way to go.
Gene-drive technology has been compared to Kurt Vonnegut’s ice-nine, a single shard of which is enough to freeze all the water in the world. A single X-shredder mouse on the loose could, it’s feared, have a similarly chilling effect—a sort of mice-nine.
when I asked around, I learned that quoll-spotting required a lot more expertise and time than I had. It would be much easier to find some of the amphibians that were killing them. So one evening I set out with a biologist named Lin Schwarzkopf to go toad hunting.
“Male toads are attracted to anything that sounds even remotely like a cane toad,” she told me. “If they hear a generator, they’ll go to it.”
“That’s why you shouldn’t hit them with a golf club. Because if you hit the glands, the poison can spray out. And if it gets in your eyes, it will blind you for a few days.”
The strongest argument for gene editing cane toads, house mice, and ship rats is also the simplest: what’s the alternative? Rejecting such technologies as unnatural isn’t going to bring nature back.
This is the situation of the Devils Hole pupfish, the Shoshone pupfish, and the Pahrump poolfish, of the northern quoll, the Campbell Island teal, and the Tristan albatross. Stick to a strict interpretation of the natural and these—along with thousands of other species—are goners.
Much closer to realization is an effort to bring back the American chestnut tree. The tree, once common in the eastern United States, was all but wiped out by chestnut blight.
(The blight, a fungal pathogen introduced in the early twentieth century, killed off nearly every chestnut in North America—an estimated four billion trees.)
Owing to this single borrowed gene, the tree is considered transgenic and subject to federal permitting. As a consequence, the blight-resistant saplings are, for now, confined to greenhouses and fenced-in plots.
The reasoning behind “genetic rescue” is the sort responsible for many a world-altering screwup. (See, for example, Asian carp and cane toads.) The history of biological interventions designed to correct for previous biological interventions reads like Dr. Seuss’s The Cat in the Hat Comes Back,
In the 1950s, Hawaii’s Department of Agriculture decided to control giant African snails, which had been introduced two decades earlier as garden ornaments, by importing rosy wolfsnails, which are also known as cannibal snails. The cannibal snails mostly left the giant snails alone. Instead, they ate their way through dozens of species of Hawaii’s small endemic land snails, producing what E. O. Wilson has called “an extinction avalanche.”
As power stations go, geothermal plants are “clean.” Instead of burning fossil fuels, they rely on steam or superheated water pumped from underground, which is why they tend to be sited in volcanically active areas.
With the superheated water inevitably come unwanted gases, like hydrogen sulfide (responsible for the stink) and carbon dioxide. Indeed, pre-Anthropocene, volcanoes were the atmosphere’s chief source of CO2.
Instead of allowing the carbon dioxide to escape into the air, the Hellisheiði plant would capture the gas and dissolve it in water. Then the mixture—basically, high-pressure club soda—would be injected back underground.
“At the beginning of the cycle, the equipment sucks in air,” she went on. “The CO2 sticks to specific chemicals inside the capture unit. We heat up the chemicals and that releases the CO2.” This CO2—the Climeworks CO2—is then added to the club-soda mixture from the power plant as it makes its way to the injection site.
Even without any help, most of the carbon dioxide humans have emitted would eventually turn to stone, via a natural process known as chemical weathering.
Aradóttir had brought along a rock core to show me the end result. The core, which was roughly two feet long and a couple of inches in diameter, was the dark color of the lava fields. But the black rock—basalt—was pocked with little holes, and these holes were filled with a chalky white compound—calcium carbonate. The white deposits represented, if not my own emissions, then at least somebody’s.
According to one theory, the process got under way eight or nine thousand years ago, before the dawn of recorded history, when wheat was domesticated in the Middle East and rice in Asia. Early farmers set to clearing land for agriculture, and as they chopped and burned their way through the forests, carbon dioxide was released. The quantities involved were comparatively small, but, according to advocates of this theory, known as the “early Anthropocene hypothesis,” the effect was fortuitous. Owing to natural cycles, CO2 levels should have been falling during this period. Human intervention
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As water power gave way to steam power, CO2 emissions began to rise, at first slowly, then vertiginously. In 1776, the first year Watt marketed his invention, humans emitted some fifteen million tons of CO2. By 1800, that figure had risen to thirty million tons. By 1850 it had increased to two hundred million tons a year and by 1900 to almost two billion.
