Gene drives as a mechanism for eradicating invasive species

“Genetic engineering”. The very mention of it is enough to provoke a furious waving of hands followed by a litany of rhetoric that wouldn’t be out of place in the Old Testament.

biblical plagues

My name is David Iorns and I’m a geek. Most of the time a computer geek but increasingly a science geek as well. I’m currently sequencing the genomes of known living kakapo and one day I would like to revive the moa (or at least a chimera that’s extremely “moa-esque”). I also have the unenviable task of promoting genetic engineering in a country where popular opinion is more or less universally opposed to the idea.

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With introductions out of the way let’s start the conversation. First of all let’s talk about genetic engineering. What exactly is it? The Cambridge Dictionary defines genetic engineering as (the science of) changing the structure of the genes of a living thing in order to make it healthier, stronger, or more useful to humans.

‘Changing the structure of the genes of a living thing in order to make it… more useful to humans’. That sounds strangely familiar.

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You guessed it. New Zealand has been genetically engineering organisms for years. It turns out we’re really very good at it. Agriculture accounts for about two thirds of New Zealand’s exports and many of those exports are animal breeds we’ve engineered. The Corriedale, the New Zealand Romney, the Drysdale, the Perendale… I could go on. There’s a long and comprehensive list of animals engineered by kiwis in New Zealand to be more useful. It’s important to understand that humans have been changing the genes of organisms to fulfill their requirements for millennia and not everyone who participates in genetic engineering is wearing a lab coat.

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There is wisdom in being cautious about the application of all new technologies. I will discuss that point further below but for now if I only succeed in convincing you the reader of one thing I hope it’s that genetic engineering is a very broad label. Let’s try to break down the negative stigma surrounding that term. Genetic engineering shouldn’t conjure images of evil scientists manufacturing the end of the world. It should conjure images of evil pugs manufacturing an apocalypse of cuteness! Or perhaps just images of pugs, French Bulldogs and Siamese cats (to name just a few of our most beloved creations).

The State of New Zealand

Let’s talk about the current state of New Zealand. Isn’t it clean and green? Isn’t it pristine and untouched? Unfortunately the answer is not as much as many may think. Permit me to summarize as briefly as possible the last 1000 or so years of New Zealand’s ecological history.

Our Flora

Prior to Māori arrival, New Zealand was almost entirely forested, besides high alpine regions and those areas affected by volcanic activity. Māori began settling the country about 1000 years ago and reduced the amount of forest cover with the use of fire. By 1840, when Europeans were a small part of the total population, the forest cover had been reduced from 85% down to 56%.

When the first Europeans arrived, in 1772, there was still thick, dense forest cover. The slash and burn technique was used often for land set aside for farming... This led to thousands of acres accidentally burned and destroyed. After the Treaty of Waitangi was signed in 1840, settlers begin a rapid expansion. Deforestation continued for many uses... An estimated 50,000 acres (200 km2) land was also lost due to human caused forest fires within only a few days. In 2010 31.40% of New Zealand was covered by forest.

So to cut a long story short in less than a thousand years we’ve destroyed 70% of our forests.

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Our Fauna

Our fauna hasn’t fared much better than our flora. Let’s examine this incomplete and somewhat depressing list of species that went extinct after (and often as a direct result of) human colonisation.

extinctions 1extinctions 2

Invasive Species

Finally there’s the invasive species. In addition to destroying much of our native flora and fauna we’ve also managed to introduce a number of species that harm our native populations. This harm continues to this day even after we’ve realised the error of our ways and are attempting to rectify our mistakes.

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Rectifying our Mistakes/Future Direction

Hindsight is 20/20 and we cannot dwell on the mistakes of the past. Attitudes around the value of our biodiversity have shifted and most of us agree that we must protect our environment for the benefit of all New Zealanders.

Some decisions are relatively straightforward. There are few who oppose the creation of protected national parks. These areas of natural beauty and ecological importance are set aside for the enjoyment of all New Zealanders and for the preservation of many of our remaining native species.

parks

Other decisions are less straightforward. One of those less straightforward decisions is what to do about invasive species in New Zealand.

When it comes to invasive species there are basically two schools of thought. There are those who believe that invasive species are just a part of evolution, i.e. survival of the most adaptable. Species have been introduced to new environments since life existed on earth and what is happening in New Zealand is just another chapter in that story. Therefore it’s futile to resist and we should simply let nature take it’s course. Then there are those who believe in taking action to reverse the decline of our native species. Those who see biodiversity in New Zealand that has taken 80 million years to evolve being destroyed in just a few hundred and want to prevent that from happening further.

red or blue

An important thing to note is that no decision is a decision in itself. Many of our native species are unable to cohabitate with introduced species. If we don’t take take more drastic action now these species will go extinct.

The New Zealand Government has declared the objective of eradicating invasive predators from mainland New Zealand by 2050. By doing this they have positioned themselves firmly in the fight back camp. There are many who are cynical about the feasibility of this objective but there are others - myself included - who are galvanized by the ambition of this goal. If we are indeed going to fight back and if we are to succeed then we must objectively explore all of the possible tools we can use to achieve a pest free New Zealand.

Gene Drives

So via a rather long introduction we arrive at the main topic of this blog post, gene drives. When it comes to eradicating invasive species we currently have two main weapons. Trapping and poison. Via these tools we have achieved strong results. We’ve cleared many of our smaller islands of invasive predators and brought critically endangered species back from the brink of extinction thanks to these island sanctuaries. Trapping and poison will remain key components in our efforts to eliminate invasive species particularly when projects like Cacophony are making order of magnitude improvements to the effectiveness of traps. However we’re unlikely to be able to achieve complete invasive species eradication using trapping and poison alone. Thankfully gene drives offer a third option that is potentially both more effective and more humane.

Gene drive is the practice of “stimulating biased inheritance of particular genes to alter entire populations”. Possible alterations include adding, disrupting, or modifying genes, including some that reduce reproductive capacity and may cause a population crash.

Basically what this means is that thanks to massive advancements in gene editing technology achieved only in the last 5 years it’s now possible to make a precise gene edit and have that edit propagate throughout an entire species.

gene drive

A Hypothetical New Zealand Use Case

To better explain the ramifications of this technology let’s talk about a hypothetical New Zealand use case. The possum is an invasive species that we’re looking to eradicate. Let’s say that thanks to gene drives it’s possible to knock down the female-specific transcript of the doublesex gene (dsx) in possums. Dsx is the bottom most gene of the sex-determination cascade. By modifying this gene expression it’s possible to ensure predominantly male progeny. This means we could genetically modify a possum that gave birth to overwhelmingly or even exclusively male offspring.

So the possum gives birth to only males, so what? Because gene drives enable the genetic change to propagate in a dominant fashion (in an optimal scenario it’s passed on to all offspring) then all future offspring will express this modification and therefore all future matings will produce all male offspring. Obviously males can’t give birth so assuming you can spread the change throughout the population you can eventually eradicate the population as eventually no females will exist to reproduce with.

If this sounds like science fiction it isn’t. This use case has already been demonstrated to work in mosquitos. There’s still a lot of research to complete in order to apply these techniques to our own target species but the underlying science is robust.

A Bottle and a Genie

Hopefully you now have an understanding of the power of gene drives. So let’s modify some possums, release them and see what happens right? No. This is absolutely not the approach I am advocating. I am advocating for highly controlled investigatory research into this technique for invasive species eradication. The famous Harvard Geneticist George Church has this to say about the powerful new genetic technology we have available:

I worry about a lot of things. I encourage people to worry about a lot of things, but worry in the sense of taking action, doing something about it and being cautious as you do something about it—doing safety engineering. Every field of engineering has a safety component, eventually. You have civil engineering, aerospace, and so forth; huge amounts of their budgets go to safety components, and biology is no exception.

In other words proceed with great caution but proceed. This is an opportunity for New Zealand to lead the world in the development of these new tools for conservation. If we choose to maintain the ultra conservative path that we’ve followed to date with regards to genetic engineering we will lose the opportunity to lead the world in a technology of great global importance and we may also lose the battle to save our most precious of native species. If we’re truly to embrace the vision of a New Zealand free of invasive predators we must explore all options to achieve this objective including gene drives.

David Iorns

David Iorns

Tech entrepreneur at Science Exchange
Founder of Genetic Rescue