How to Exterminate the Invaders: Playing Dangerously with the Pandora’s Box of Genetic Engineering

How to Exterminate the Invaders: Playing Dangerously with the Pandora’s Box of Genetic Engineering
How to Exterminate the Invaders: Playing Dangerously with the Pandora’s Box of Genetic Engineering

Man has dragged alien species to new continents, sometimes inadvertently and often intentionally. That’s how she got from America to Europe Musk Muskrat (Ondatra zibethicus) whose nutria (Myocastor coypus). He traveled in the opposite direction across the Atlantic, for example common starling (Sturnus vulgaris) or field lark (Alauda arvensis). Sometimes the transoceanic import passed without consequences, other times it started a natural disaster. Undoubtedly, the most famous destructive invasion was caused by the deliberate importation of the wild rabbit (Oryctolagus cuniculus) to Australia.

Australia overrun with rabbits

The rabbits reached Australia in the hold of eleven ships that set sail from the English port of Portsmouth on May 13, 1787, to establish a penal colony on the smallest continent. At first it seemed like a good idea, as the colonists had a plentiful source of tasty meat in rabbits. But 40 years later, it was clear that rabbits should never have set foot on Australian soil. In Tasmania, they flooded the countryside by the thousands. On the Australian mainland, they were still more or less under control because people kept them in high stone enclosures from which the animals could not escape.

A major turning point came in 1858, when a breeder released rabbits in order to shoot them. A year later, another Australian hunting enthusiast had two dozen wild rabbits imported from England and also released them into the wild on his property. In 1866, Australia already faced the first rabbit plague, but attempts to extinguish the “rabbit fire” failed miserably. In 1907, Australians built 3,256 kilometers of fences in the path of a rabbit invasion. The longest crossed the western part of the continent from north to south with a length of 1,833 km. That didn’t stop the rabbits either.

Deployment of bacteria and viruses

Using the example of Australian rabbits, one can vividly document the difficulties that stand in people’s way when they try to correct the consequences of an earlier ill-advised introduction of an animal into a new environment.

Attempts to eradicate the hopping invader date back to the end of the 19th century, when the New South Wales government offered a £25,000 reward for an effective recipe to eradicate the rabbit population. The impressive reward also attracted the famous French biologist Louis Pasteur. He suggested infecting rabbits with a bacteria he had discovered himself. A microbe later named in honor of its discoverer Pasteurella multocida although it infected the rabbits, it was not enough to exterminate them.

In 1950, the myxomatosis virus was purposefully spread among Australian rabbits. Animals were dying by the thousands and their health conditions had dropped to a sixth. Out of six hundred million, “only” 100 million survived. However, these rabbits developed a resistance to the deadly disease and myxomatosis was thus eliminated in their further struggle to rid Australia of rabbits.

Rabbits resist traps

By the early 1990s, the Australian rabbit population had reached 300 million again, so the Australians decided to test another virus. This time the choice fell on calicivirus causing a fatal disease. Preliminary tests began in 1991 on Wardang Island, with the understanding that the contagion must not spread to the mainland under any circumstances. The possible deployment of the virus on the Australian continent was to be decided only on the basis of the test results from Wardang. However, as early as 1995, the disease was killing rabbits on the mainland. Was it an accident or sabotage? We will probably never be definitively clear.

In 2017, an even more effective type was released into the wild rabbit population calicivirus in the hope that the pest, which threatens 150 species of native Australian fauna and causes $200 million in damage to farmers every year, will disappear for good. However, it is quite likely that the rabbit will survive even this battle in the war for its extermination. That’s why the Australians are thinking about deploying a genetic weapon known among experts as a “gene drive” against rabbits.

A non-negotiable hereditary predisposition

Behind the scientific term “gene drive” hides an artificially prepared hereditary predisposition, which spreads through the population like wildfire through an arid savannah. With its help, the entire population is “rewritten” within a few generations, and all its members become carriers of a new trait.

Traditional genes are inherited by the offspring from one copy from each parent, while the father and mother can each pass on a different variant of the gene. In the case of a trait that acts as a gene drive, however, it doesn’t matter at all what trait the offspring “paired” with it received from the other parent. The gene drive rewrites itself into the second trait coming from the other parent.

The result of this gene drive action looks as if one parent passed on a pair of gene drives to the offspring and the transmission of the gene from the other was completely blocked. Therefore, Mendel’s laws do not apply to gene drive, which states that the gene of one parent is inherited by half of the sons and daughters, a quarter of the grandsons and granddaughters, and an eighth of the great-grandchildren. The gene drive is built to be inherited by all sons and daughters, all grandchildren and all great-grandchildren. It will completely dominate the population and will never disappear again.

Flies under strict supervision

Geneticists invented the gene drive a long time ago, but the implementation of their idea was delayed. That changed fundamentally nine years ago with the discovery of a genetic engineering technique known as CRISPR-Cas9. This allowed an unprecedented precision of intervention in hereditary information. Until then, genetic engineers were “shooting blind” because they had no control over where they would alter the hereditary information. The CRISPR-Cas9 technique has replaced “shooting in the dark” with “sharpshooting” that even William Tell would not be ashamed of. At that moment, the possibility opened up to create a functioning gene drive, i.e. a gene that spreads through the population by a chain reaction and whose representation can only increase.

American scientists were the first to create a perfectly functioning gene drive Ethan Bier and Valentino Gantz in 2015. They inserted it into the fruit fly’s genetic information and thereby ensured the flies’ body color change. In a perfectly secured laboratory, they released a few individuals that had been recolored using a gene drive into a flock of wild flies. After ten generations, there were only recolored flies in the flock, and the insects with the original coloring disappeared.

From the conditions under which this experiment took place, it is clear that maximum caution is required when working with the gene drive. If Bier and Gantz escaped from the laboratory with a single fly with hereditary information enriched with a gene drive, it could “recolor” the entire wild population of fruit flies. It’s hard to say what the consequences would be. We can assume that differently colored flies would be more conspicuous to their natural enemies. Their resistance to cold or high temperatures could also change, because a differently colored body would heat up differently in the sun. We don’t know what would actually happen, because no one dares to release fruit flies with a gene drive into the wild.

Consequences as a big unknown

There are many practical uses for the gene drive. In this way, scientists have already created mosquitoes that are resistant to the causative agent of malaria. If they were released in countries where malaria still threatens the health and lives of millions of people, the gene drive would “overwrite” the genetic information of wild mosquitoes and they would lose the ability to transmit the disease to humans. Similarly, a gene drive can be spread among mosquitoes that would prevent them from spreading the Zika virus and the causative agents of many other diseases. But no one is planning anything like that, because mosquitoes occupy an important place in nature and we don’t know what we would unleash by changing their genetic information.

In nature, we could set off a domino effect in which the fragile structure of the ecosystem would collapse like a house of cards. To suppress malaria or dengue fever, we would pay with a large-scale natural disaster, and there is no recipe for eliminating such a calamity.

Single-sex population option

Invasive species of plants and animals are among those whose presence represents a major problem for nature. Their disappearance should not cause damage. On the contrary, disturbed ecosystems would get a chance to recover from the invasion of invaders and return to their original state. There are several strategies to eliminate invasive species. One of them, for example, assumes that the gene drive would spread through the population traits that ensure the development of the male sex.

Under normal circumstances, daughters and sons are born to Australian wild rabbits in a ratio of 1:1. If the father carried the aptitude for the development of the male sex in the form of a gene drive, only sons would be born to females. Clearly, a population with such a skewed sex ratio would quickly collapse.

Imported pests of New Zealand

New Zealanders are very seriously considering deploying a gene drive against animal invaders. A number of animals from Europe, Asia and Australia were introduced to the New Zealand islands. Big problems are caused here, for example, by imported from Europe ermine weasel (Mustela erminea) or a marsupial deliberately imported from Australia a piece of fox (Trichosurus vulpecula).

The hemlock destroys a number of native New Zealand fauna, but even more damage is done by the omnivorous red fox. It chooses bird nests and eats both eggs and young. However, it does not despise plant food either and devastates the original flora. For example, the tree is threatened by a species of ferrets Metrosideros robusta. Kusu eats its leaves, young twigs, buds, flowers and seeds. At the same time, the marsupial invader from Australia is a dangerous competitor for native New Zealand herbivores, who lose to it in the fight for plant food.

Like an arrow and a word

New Zealanders are considering introducing genes into the hereditary information of an ermine or a piece of fox in the form of a gene drive in laboratories. Carriers of these genes would be released into the wild, and the disease would then spread through the populations of the animal invaders until they collapsed.

So far, everything is in the stage of theoretical planning. Obviously, the slightest mistake can have unfathomable consequences, and the road to hell is often paved with the best of intentions. If, for example, a piece of fox with a dangerous gene drive were to get from New Zealand to its Australian homeland, it would threaten the original population of this marsupial throughout the continent.

Still, New Zealanders are not alone in their plans to deploy gene drives against invasive species. There is talk of plans to use this weapon for disposal rats (Rattus norvegicus) in the Galapagos or rabbits in Australia. However, there are great and justified concerns about the ill-advised deployment of gen drive everywhere. The Kalahari San say: “No one can take back an arrow shot and a word spoken!” The same applies to gene drive organisms released into the wild.

Twisted triangles

When a person introduces a new species somewhere and it becomes a disaster for its homeland, exterminating the invader may not bring the desired result. On the contrary, it can make the situation even worse. An example is introduction pigs (Sus scrofa) to the Channel Islands off the coast of California. The pigs went wild and multiplied. It devastated the local nature, rich in unique species of fauna and flora. That’s why conservationists have declared war on pigs. But with the decrease in the number of wild pigs, even the rare ones began to disappear from the island island fox (Urocyon littoralis). “What’s happening?” natural scientists did not understand.

The mystery quickly became clear. From the mainland, golden eagles learned to fly to the Channel Islands to hunt wild pigs (Aquila chrysaetos). But when the pigs decreased significantly, they began to hunt other island animals. And they liked the island fox.

TIP: Endangered marsupials serve as live poisoned baits against killer cats

Conservationists on islands in the southern seas near Antarctica are dealing with another complicated complication. Whaling ship crews dragged rats and cats here. Both animal invaders are decimating the nesting grounds of local seabirds. They destroy their eggs, kill and eat their young. Attempts to exterminate the cats have only worsened the already serious situation, as cats also hunt rats and there has been a sharp increase in the number of them on the islands without cats. Targeted action against rats meant a decrease in food for cats, and they began to attack the birds with greater vigor. The only chance for success lies in the current vigorous and rapid extermination of both cats and rats.

The article is in Czech

Tags: Exterminate Invaders Playing Dangerously Pandoras Box Genetic Engineering

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