Australia’s feral cat  problem could be fixed with powerful new gene editing tools

A few years ago, as dusk descended in Victoria’s Great Otway National Park, I left my campsite, torch at the ready.

I was on the lookout for little marsupials emerging to start their night-time foraging.

Instead, I was confronted with the glowing eyes of a feral cat among the ferns. 

We were probably out looking for the same thing.

The impact of feral cats and other invasive species is felt across Australia. Not only do they threaten native species, but they can also spread diseases to humans and livestock.

Invasive species are estimated to cost Australia an eye-watering $25 billion dollars annually, while the global cost is a staggering $423 billion.

One species consistently tops the list as “Australia’s worst”: feral cats.

Feral cats are everywhere — the nation is home to up to 6.3 million of them, and they are responsible for killing millions of native mammals, reptiles, and birds each day. 

Minister for the Environment and Water Tanya Plibersek recently declared “war on feral cats”, announcing plans involving cat curfews, desexing regulations, and caps on cat numbers in homes.

But what can we do about the millions of feral cats already wreaking havoc across Australia? And what about other pests such as foxes, rabbits, cane toads, carp, pigs, deer, or goats?

One technique with the potential to help fight not just cats but all invasive species is called a “gene drive”.

What is a gene drive?

All living organisms store genetic information in their cells as long strands of DNA. Sections of these strands are called genes, which give rise to different traits, such as eye colour.

Like most animals, cats have two copies of each gene: one inherited from each parent. This means that normally, a cat will pass one gene copy onto half of their kitten offspring.

But a gene drive does not follow usual inheritance rules.

A gene drive is a gene or collection of genes that rapidly spread from one generation to another.

Even if only one parent has a gene drive, they can pass it on to more than half of their offspring, and in some cases, to all of them.

It’s why gene drives are sometimes called “selfish”.

Gene drives are found in nature — researchers at the University of Adelaide are investigating a naturally occurring mouse gene drive to spread infertility to female mice.

But they can also be created in the lab using CRISPR gene-editing technology

Lab-developed gene drives can be designed to do different things.

A gene drive to reduce the number of mosquitoes that transmit malaria has been developed, and in 2019, mice became the first mammal to be engineered to contain a gene drive in their DNA.

Since then, no other gene-drive mammals, including cats, have been produced.

But if a gene drive for feral cats was developed, it could involve spreading a gene through the population that renders females infertile, or tailored so only male offspring are born.

Over time, the feral cat population would drop, then crash.

What’s the risk to native wildlife?

Gene drives can be restricted to a target species, such as cats, without the chance of spreading to Australian wildlife.

That’s because gene drives are passed down from parent to offspring.

Most of Australia’s invasive species cannot interbreed or produce offspring with native wildlife, which means almost all invasive species in Australia could be controlled using gene drives.

The exception is wild dogs, which can breed with dingoes.

It is also important to consider that an animal that may be a pest in Australia, such as the cane toad, may not be a pest in their native range.

While cane toads have been linked to the extinction of several species in the Northern Territory and Queensland, they play an essential ecological role in their native range in Central and South America.

So how would we stop a gene-drive cane toad from leaving Australia and harming its native populations?

First, Australia’s border security would need to pay as much attention to what departs Australia as what enters, ensuring potential gene-drive animals don’t leave.

Second, animals resistant to gene drive technology could also be provided to regions where a target species is native.

So, if a gene drive cane toad ever made it out of Australia and back to its native range, a population of gene-drive-resistant toads could be waiting to stop the gene drive from spreading.

How long before we see results?

Unfortunately, current estimates for a gene drive to make a noticeable impact on invasive species are in the order of decades, even in species that produce multiple litters a year.

A rabbit gene drive would take approximately 17 years to halve the Australian rabbit population.

This time frame could be shortened by, for instance, increasing the number of gene-drive animals bred in captivity then introducing them into the target population.

While the current time estimates for gene drives are long, there are no stand-out alternative strategies that could reduce invasive species anywhere near as effectively in the long term.

It is still early days for gene drives. Developing the technology will take many years.

It will — and should — also be the subject of intense scientific scrutiny and careful analysis.

In a country as vast and complex as Australia, eradicating invasive species on a large scale is currently impossible.

Gene drives may finally offer some hope for the billions of native animals lost every year and the significant losses experienced by farmers and landowners because of invasive species.

And if a gene drive for cats was developed, I would undoubtedly have more success spotting small marsupials on my camping trips.

Ellen Cottingham is a postdoctoral research fellow at the University of Melbourne. She is also one of ABC RN’s Top 5 scientists for 2023.