Rodents on Islands
Island ecosystems are uniquely vulnerable and ill-suited for testing experimental gene drive technologies which can have unpredictable, irreversible impacts. In biodiversity hotspots, conservation efforts should prioritise approaches supported by strong evidence of effectiveness. Relying on gene drives instead of proven methods risks wasting valuable time while endangered species continue to decline.
Islands: Biodiversity hotspots at risk
Although islands make up just 5.3% of Earth’s land area, they are home to about 17% of the world’s bird and plant species1 – and account for around 75% of known extinctions.2
Invasive species are the main driver of these losses. Birds, particularly ground- or burrow-nesting species, are highly vulnerable to invasive rodents.
The most effective defence is strict biosecurity. Where invasives are already established, eradication programmes have often reversed the damage – though not always on the first attempt.
Can genetic engineering help eradicate invasive species?
Some molecular biologists and conservationists believe that genetic engineering could strengthen current and future eradication efforts.3 They are exploring gene drives – a controversial technology that biases inheritance so engineered traits are passed on to 90–99% of offspring, rather than the usual 50%, allowing them to spread quickly through populations.
Experiments so far focus largely on house mice (Mus musculus), though there is also emerging work in rats. Proposed traits, such as female infertility and biased sex ratio, aim to hamper reproduction.
However, once released, gene drives are difficult to control or reverse. What counts as ‘safe’ or ‘appropriate’ use remains unresolved,4 and ecological, cultural, and ethical concerns persist.5
Gene drive technology faces major technical hurdles
Formed in 2016, the Genetic Biocontrol of Invasive Rodents (GBIRd) partnership leads efforts to use gene drives to eradicate invasive rodents.
Results are far from guaranteed:
- Still in early stages: After nearly a decade and millions in grants, gene drive technology remains in early lab phases, mainly focused on mosquitoes.6 No empirical evidence exists of a gene drive functioning in a vertebrate under field conditions.
- Limited effectiveness in rodents: Gene drives are less effective in rodents due to DNA repair mechanisms that block intended edits and polyandry (females mating with multiple males).7
- Slow population impact: Models suggest a population of 200,000 mice could be eliminated in less than 10 years, assuming six breeding cycles per year.8 However, researchers with direct knowledge of mice biology estimate only 0.5–2 cycles per year, fewer in colder climates,9 meaning eradication could take much longer.
- High and uncertain costs: No credible real-world costings exist. In 2019, GBIRd estimated US$16–22 million for confined trials over 4–5 years.10
Ecological risks: What could go wrong with gene drives?
While islands may seem isolated, they are ecologically connected via ocean currents, seabird movements, and human transport, offering potential pathways for unintended spread.11 Rodents, invasive in some regions, are native in others. If gene drive-modified rodents reach those regions, they could pose an existential threat to native species and food webs12 and disrupt entire ecosystems.
Biosafety frameworks fall short for gene drives
Current biosafety rules were established for earlier technologies and are ill-suited to manage the additional and unique risks of gene drives.5 They were never designed for self-propagating organisms that spread through ecosystems.
Effective oversight of gene drives would require unprecedented international cooperation – yet no mechanisms exist for long-term monitoring or cross-border accountability.
Proven methods deliver faster, more reliable results
Rodents have been eradicated from more than 700 islands worldwide.13 Even in remote sub-Antarctic islands, the success rate is good. Australia’s Macquarie Island is now free of cats, rabbits, rats, and mice, and New Zealand’s Campbell Island of sheep, cats, and rats. Not all efforts succeed – mice persist on France’s St Paul Island (though rats were eliminated), and they survived the UK’s 2021 eradication attempt on Gough Island.14
A 2022 review of 1,550 eradications on nearly 1,000 islands since 1872 found an 88% success rate using hunting, trapping, and targeted poisoning methods. While the number of projects is declining, the total area treated continues to expand. Larger, inhabited islands increase complexity, cost, and risks of failure or unintended impacts.15
Effective oversight of gene drives would require unprecedented international cooperation
Developed and used for more than 40 years,13 conventional methods can achieve complete eradication in just 2-4 years. By contrast, experimental gene drives are unlikely to deliver similar results in less than 25 years – and even longer in sub-Antarctic regions where rodents reproduce more slowly. Relying on gene drives instead of proven methods could waste critical time for declining bird populations.
Sources
- Tershy BR et al (2015). The Importance of Islands for the Protection of Biological and Linguistic Diversity. BioScience https://academic.oup.com/bioscience/article-abstract/65/6/592/301848?redirectedFrom=fulltext [↩]
- Fernández-Palacios JM et al (2021). Scientists’ warning – The outstanding biodiversity of islands is in peril. Global Ecology and Conservation. https://www.sciencedirect.com/science/article/pii/S2351989421003978?via%3Dihub [↩]
- Island Conservation press release (2022). https://www.islandconservation.org/island-communities-threatened-by-invasive-rodents-have-potential-new-tool-to-consider-for-conservation-toolbox [↩]
- Hartley S et al (2022). The principles driving gene drives for conservation. Environmental Science and Policy. https://www.sciencedirect.com/science/article/pii/S1462901122001514 [↩]
- Critical Scientists Switzerland (2019). Gene drives: A report on their science, applications, social aspects, ethics and regulations. https://genedrives.ch/report [↩] [↩]
- Gene Drive Monitor Website. https://genedrivemonitor.org [↩]
- Manser A et al (2019). Controlling invasive rodents via synthetic gene drive and the role of polyandry. Proceedings of the Royal Society B. https://pmc.ncbi.nlm.nih.gov/articles/PMC6732378 [↩]
- Birand A et al (2022). Gene drives for vertebrate pest control: Realistic spatial modelling of eradication probabilities and times for island mouse population. Molecular Ecology. https://onlinelibrary.wiley.com/doi/10.1111/mec.16361 [↩]
- Bronson FH (1979). The Reproductive Ecology of the House Mouse. Quarterly Review of Biology. https://www.journals.uchicago.edu/doi/10.1086/411295 [↩]
- USDA Wildlife Services – Staff Publications 2235 (2019). https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=3234&context=icwdm_usdanwrc [↩]
- Greenbaum G et al (2021). Designing gene drives to limit spillover to non-target populations. PLOS Genetics. https://pmc.ncbi.nlm.nih.gov/articles/PMC7943199 [↩]
- Yoshida K et al (2019). Ecosystem changes following the eradication of invasive species: Evaluation of various eradication scenarios by computer simulation. Ecological Modelling. https://www.sciencedirect.com/science/article/abs/pii/S0304380019303394 [↩]
- Mouse Free Marion Project website. https://mousefreemarion.org/faq [↩] [↩]
- Agreement on the Conservation of Albatrosses and Petrels website (2024). What is the “state of play” with planned predator eradications on two sub-Antarctic islands? https://acap.aq/latest-news/the-acap-monthly-missive-what-is-the-state-of-play-with-planned-predator-eradications-on-two-sub-antarctic-islands [↩]
- Spatz DR et al (2022). The global contribution of invasive vertebrate eradication as a key island restoration tool. Scientific Reports. https://www.nature.com/articles/s41598-022-14982-5 [↩]