Mutant grey squirrels, genetically modified to spread infertility genes, could be released into the wild to tackle the burgeoning population, the University of Edinburgh has said.
North American grey squirrels were imported to Britain in the mid-19th century by landowners, and their population has now grown to more than two million.
Not only do they out-compete the native red squirrel, they also strip trees of their bark, causing a threat to woodlands, as well as preying on eggs and chicks.
The Department of the Environment (Defra) is currently looking at options for controlling grey squirrels with culls and oral contraceptives being considered.
Now the University of Edinburgh has suggested that genetically altering squirrels so they pass on infertility genes could dramatically cut populations.
In a new study, published in the journal Scientific Reports, researchers found that releasing just 100 mutated squirrels into a population of 3,000 greys would wipe out the population within 15 years.
The technique is known as a gene drive, and has already been successfully used to dramatically lower populations of mosquitoes to prevent malaria and Zika.
It works by preventing natural selection from weeding out harmful traits like infertility, essentially “driving” an unhelpful mutation through a population.
Scientists insert the new genetic code using a process called Crispr – essentially molecular scissors which snip away parts of the DNA and replace it with new code.
Writing in the journal, the authors said: “Without intervention, red squirrels could be lost from the UK mainland within the next few decades.
“Current control methods such as shooting, trapping, and poisoning are inhumane, labour-intensive, expensive, and ineffective in dealing with the scope of the problem in most situations.
“Although there are still technical challenges, Crispr-based gene drives may offer a humane, efficient, species-specific and cost-effective method for controlling invasive species, including grey squirrels in the UK.”
In January, Lord Goldsmith, the environment minister, said that the breeding infertility into grey squirrels could provide a “longer term” and “more humane way” of reducing numbers.
The Royal Forestry Society is currently calling for a grey squirrel cull and is also funding research into contraception. But experts said a gene drive could offer a new solution.
Commenting on the new study, Professor Luke Alphey, group leader in Arthropod Genetics at The Pirbright Institute, said: “Invasive species are a major problem for biodiversity and conservation, in many cases there are no adequate methods for control.
“Most work on gene drives has focused on mosquitoes; this study is unusual in focusing on a vertebrate, the grey squirrel, though there has also been interest in targeting invasive populations of mice and rats on islands.
“Regulatory approval and public acceptance would obviously be essential before any actual use of such technology – that is a long way off, but this paper indicates that gene drives could be a valuable tool in the conservation toolbox.”
The authors say the gene drive technique has not yet been tested in live animals, and further research is needed to ensure an abrupt suppression of the grey squirrel population does not have a damaging impact on the ecosystem as a whole.
There are also concerns that a large-scale release of animals in an environment – which already has too many – may lead to starvation or mass migration of the population, spreading the problem even further.
The new technique combines three types of gene drive, including one which limits how long the effect lasts for in case of unexpected impacts.
New mutated animals would need to be added over time to continue the suppressive effect, the researchers said.
Dr Tony Nolan, senior lecturer at the Liverpool School of Tropical Medicine (LSTM), added: “Demonstration of its practical feasibility would be a significant milestone. In the meantime, studies like this are useful for informing conversation about the relative merits of gene drive for controlling grey squirrels, and more broadly as a potential new conservation tool to protect endangered species.”