Photo by Chantal Steyn of Gough Island albatross on Flickr

Invasive Mice and Engineered Genes

W.M. Adams and K.H. Redford

On Gough Island, a steep speck of land deep in the South Atlantic, giant mice eat albatross chicks as they sit on their nests. They are house mice, accidental arrivals on the ships of long-dead sealers. But they have lost their secretive, timid, mousy ways. Over numerous generations, on an island without predators, they have become predators themselves. They have grown bigger, and fierce. The internet offers gruesome videos of Tristan albatross chicks being eaten alive in the night.

The house mice of Gough Island are examples of one of the most serious and intractable drivers of biodiversity decline, invasive species. Not all species introduced by people outside their normal range become invasive, but invasive species are the most common threat to amphibians, reptiles, and mammals on the IUCN Red List, and have been a contributing cause in a quarter of plant extinctions and a third of animal extinctions in recent centuries.

Traditional tools for addressing invasive species include traps, guns, fences, and particularly poisons. Though often effective, these often have undesired, and sometimes unexpected, knock-on effects on native species. Synthetic biology, the application of new genetic tools like CRISPR, is being explored as a source of new approaches to control with fewer side effects. The use of such methods in conservation blurs the distinction between what is natural and what is human-made.

The threat of introduced rodents to seabirds on oceanic islands is well known, and there have been many projects across the world to eradicate them. Although there is a growing industry designing and selling ingenious invasive-species specific traps, the dominant way of eradicating invasive rodents and other predators is to use poison. On Gough Island, the UK conservation organization the Royal Society for the Protection of Birds has a project to eradicate the mice, using helicopters to spread cereal bait pellets containing rodenticide. This is both time-consuming and expensive. On the large South Atlantic Island of South Georgia, eradication of rats cost $11m, a total of $104 per hectare treated. And there can be collateral damage. On Gough Island, the endemic Gough moorhen population had to be captured and kept in captivity in case of accidental mortality.

What if there were another way of controlling invasive species? What if the threat could be eradicated without bloodshed, without poison, without helicopters? Conservation scientists have identified such a technique, attacking invasive species at the genetic level using synthetic biology. They believe they could literally breed the invasive species out of existence by creating a genetic device called an engineered gene drive.

A gene drive is one or more genetic elements that can cause biased inheritance in its favor. In other words, it is a sequence of DNA that increases the likelihood that a genetic characteristic will be passed from one generation to the next through sexual reproduction at greater than the normal 50% chance of inheritance. When scientists engineer a gene drive, they can “harness” to it a genetic sequence designed to affect the entire population that will be “driven” into the genomes of all individuals in the population.

Though gene drives occur naturally, they are increasingly being created by genetic engineering, using the techniques of gene editing (often described as analogous to editing a sentence with a word processor to delete words or correct spelling mistakes). Gene editing using genetic devices such as CRISPR to cut genes and insert new genetic sequences or delete old ones. It is for this discovery that Jennifer Doudna and Emmanuelle Charpentier received the Nobel prize in Chemistry in 2020.

An international partnership called GBIRd (“Genetic Biocontrol of Invasive Rodents”) is investigating the potential use of an engineered gene drive to modify mouse genomes so that all offspring are of a single sex. If mice carrying such a gene drive were released into the wild on an island, the target genes controlling the sex of offspring would spread throughout the population. Within a few generations all mice on the island would be the same sex, and the population would die out, because there could be no further breeding.

This may sound like science fiction, but it is not. Scientists know how to create the drives, and know enough about the mouse genomes to see genes to target. This is workable, everyday science. However, it is not yet accepted by either governments or the public.

The engineering of the genomes of wild species raises all kinds of questions for conservationists, and the communities on whose behalf they seek to save nature. Questions range from the practical to the ethical, from broad questions about the wisdom or acceptability of changing the genomes of wild living animals and plants to the risks of releasing something like a gene drive, or an organism genetically engineered in some other way, into the wild.

Debate about gene editing in wild species has barely begun. But the number and diversity of ideas for conservation applications mean that it is both important and urgent. A critical factor will be what the public thinks of the idea of conservationists (whose entire raison d’etre is to protect nature) starting to re-engineer it at the genetic scale. The precedent of the bitter debate about genetically modified crops emphasizes the risks of scientists, business, and government regulators embarking on something that has not been accepted by the public.

Recently, Australia’s National Science Agency (CSIRO) decided to ask what the Australian public thought of the application of synthetic biology in wildlife conservation. Responses on the use of synthetic biology to manage invasive pest species was interesting. Almost everyone polled (94%) was aware that invasive pest species were a big problem in Australia. On the use of synthetic biology to control them, 59% supported such applications, 29% were neutral, and 12% were opposed. When asked about the use of this technology in their local area, 53% indicated that they would not be bothered, while 47% indicated that they would be moderately or seriously bothered.

Polls like this are valuable, although too few and far between to provide much guidance to government regulators, or to conservationists eager to deploy new genetic tools in their fight to protect biodiversity. Public thinking about science and scientists, about novel technologies and about nature and naturalness, is subtle and complex. But one thing this Australian poll does show is the importance of debate about the application of synthetic biology in conservation.

Kent H. Redford is Principal at Archipelago Consulting and has worked for The Nature Conservancy and the Wildlife Conservation Society. William M. Adams is Emeritus Moran Chair of Conservation and Development at the University of Cambridge.

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