Breeding out the feral cat problem
While feral cats have only existed in Australia for the last 200 or so years, they’ve left a destructive mark on our landscape, contributing to a growing list of Australian native animals that have become threatened or extinct in that time.
Today, feral cats (Felis catus) are rampant in all parts of Australia, covering 99% of Australia’s total land area. That includes ecosystems from deserts to forests and grasslands, and even many of our offshore islands.
Though they might share their species name and genome with their domestic counterparts, that’s where their similarity ends, explains Biosecurity Research Director at CSIRO, Dr Raghu Sathyamurthy.
“Feral cats are opportunistic predators. They’re one of the most significant threats to our native species including small mammals, birds and reptiles,” says Dr Sathyamurthy.
He adds, “We can be fairly certain that they’ve contributed to the extinction of at least 20 Australian mammal species since colonisation.”
Take the Desert bandicoot (Perameles eremiana). Once abundant in the arid country of central Australia, now considered extinct. Or the Mountain pygmy possum (Burramys parvus), currently listed as critically endangered, with fewer than 2,000 of their kind left in the wild.
1.8 billion animals a year
Current estimates are that feral cats kill an average 1.8 billion Australian animals (reptiles, frogs, birds and mammals) every year, or two thousand native animals every minute.
A new type of genetic technology using CRISPR–Cas9, called ‘gene drive’, offers some hope.
It could theoretically be used to suppress populations of invasive pests in parts of Australia. However its potential use in vertebrates, like feral cats, is some way off in most cases (at least ten years).
Gene drive is one of several potential applications of synthetic biology, an area of research that CSIRO has invested in, to build greater scientific capability within Australia over the past five years. Dr Aditi Mankad, Senior Research Scientist at CSIRO, leads a team of social and behavioural scientists exploring the social and economic research aspects of this program.
How gene drive works to control invasive species
Gene drive works by influencing the likelihood of offspring to inherit a certain genetic trait. An enzyme called Cas9, which can cut DNA, could, for example, deliver instructions to shed the X chromosome. This would virtually guarantee the cat’s offspring would be only male. With each generation, the sex imbalance would tip in favour of males, with fewer females left to reproduce. A common misconception is that gene drive might affect other species upon release, which scientists can conclusively rule out.
A single gene drive released into the environment could provide some reprieve for our native birds, reptiles and mammals, sustaining a population decline for at least a couple of decades.
The benefits are significant, and Australia is playing a leading role in the development of vertebrate genetic technologies, according to Dr Owain Edwards, a colleague of Dr Mankad, who leads the Environment and Biocontrol Domain of CSIRO’s Synthetic Biology Future Science Platform investigating the technology. But as with any new area of technology, it’s fair to say that the public would feel cautious about its deployment.
Social acceptability as key
Dr Edwards has worked in the gene technology space for over two decades.
“It’s not like these kinds of technologies can be released overnight,” he says. “Over the last several decades, scientists have recognised that understanding how the public might feel about a certain technology – and gaining ‘social licence’, is a critical factor to successful deployment.”
“All of this research needs to take place before a trialled release, and way before genetic technologies could feasibly be integrated with current pest management practices,” says Dr Edwards.
Dr Mankad explains that in some cases, early social research can help inform technology development, via building a shared understanding of societal expectations for technology development, risk perceptions and the public’s view of the importance of this work.
That’s why her team set out to uncover the psychological and contextual factors that might influence public attitudes and concerns toward gene drive.
“We knew from previous research that there was lower overall public support for gene drive technology to solve environmental problems when compared to other synthetic biology applications. For example, genetically engineered heat-resistant coral for the Great Barrier Reef or genetically engineered fibres for industry,” says Dr Mankad.
“This study was all about taking a deeper dive into what might influence support and people’s perceptions of risk and value. We hypothesised that community or place-based factors might influence public acceptance for this technology, so we looked to explore those.”
Majority of Australians willing to support gene drive
The Report, Public perspectives towards using gene drive for invasive species management in Australia polled a total of 3,823 Australians as a representative sample of the Australian public.
The researchers produced a simple animation that was provided to survey participants, describing the feral cat problem, gene drive technology and its intended outcomes. A further “local feral cat scenario” was embedded later in the survey, prompting participants to imagine a scenario where feral cats were a problem in their local area and respond to survey questions with that in mind.
As the survey progressed, the researchers posed various questions to understand what made gene drive technology more or less favourable. This allowed them to test several hypotheses, including that cat owners may be more concerned about the consequences of gene drive, or that people who had a feral cat problem in their local area may be more supportive of feral cat management, either using gene drive technology or traditional methods of pest control.
Overall, Dr Mankad’s team found the majority of participants were in favour of gene drive technology.
Almost 68% of respondents were supportive or strongly supportive of the development of gene drive technology for pest control in Australia. A smaller fraction of participants (10%) indicated little or no support for its development.
Participants were more likely to throw support behind the future-oriented technology if they personally felt that feral cats were a problem in their local area.
When it came to when and where to implement the technology, 64% of respondents were comfortable living within 5km of the gene drive release, and another 13% within a broad 20km range. A far narrower margin of participants felt comfortable living upwards of 100km of release (8%).
What do cat lovers think?
Domestic cats (as opposed to feral cats) are often on the receiving end of criticism for the damage cats wreak on the environment. But the survey found that most cat owners would support the technology, although researchers noted that these participants indicated slightly less support than people who did not own or care for a cat.
“We also found that 82% of cat owners would desex any cats they own to prevent cross-breeding with the gene drive cats, which suggests people would be willing to engage in responsible pet ownership practices to facilitate the implementation of this type of technology”.
Was it a case of cognitive dissonance? Pet owners may witness the impact of domestic cats roaming first-hand, and Dr Mankad noted that these results may reflect increased efforts at a local level to educate cat owners on the importance of keeping pets contained.
Social science to inform synthetic biology
From here, the survey results will be used to inform scientists, policy makers, and the wider community about public views on the development and application of possible new biotechnologies in Australia.
“This research has opened an important dialogue for understanding public opinions around invasive species management, and other synthetic biology applications more generally,” says Dr Edwards.
“Gene drive technology is an example synthetic biology application that affects society more broadly, even if it was to be released in a specific geographic area.”
One of the obvious benefits of gene drive is that it offers a more humane approach to invasive species management.
Current strategies available for feral cat management vary across different states and territories including fencing, trapping, baiting and in some cases, shooting.
Generally, experts agree that none of these methods, even when combined, are keeping pace with the catastrophic impact that feral cats wreak on native wildlife.
More information on gene drive for invasive species management
Read the report on the CSIRO website.