One might mistake mice for monsters. They've wreaked havoc on delicate native ecosystems—consuming rare and endemic plants, insects, and even unsuspecting seabirds.
But it's not fair to blame the mice—they were just doing what mice do.
Human travelers are the real culprits. As stowaways on ships, mice have inadvertently been transported to islands all over the world where there are no natural predators to control their populations and keep them from booming. Islands are a conservation concern as they are home to 40 percent of all endangered species and 80 percent of all extinctions have occurred on islands.
To combat these invasive hordes, people have tried many methods including traps and poison. However, reducing mouse populations has proved a thorny problem on many islands. With an abundance of food, few or no natural enemies, and an impressive breeding ability, their numbers can increase rapidly.
But now humans may be in a position to solve the problem they created. I am part of an interdisciplinary graduate program at North Carolina State University that is collaborating with the non-profit group Island Conservation. We explore not only the science, but also the moral, ethical, legal, and public perspectives on potentially using a genetically modified mouse to rid an island of invasive house mice for conservation purposes.
Our group is currently investigating new biotechnology that could reduce or even eliminate these invasive mice. The project involves designing a genetically modified mouse that can do two things: spread a gene and only have male offspring.
A monk named Gregor Mendel demonstrated that inheritance of genes tends to follow pretty simple rules. We tend to inherit two copies of each gene, one from mom and one from dad. Now, imagine your dad has straight hair and carries two genes for straight hair. Your mom has curly hair but one of her genes is curly, the other is straight. Because the curly-hair gene is dominant, you had a 50:50 chance of having curly hair yourself: if her curly gene found its way into
into the particular egg that gave rise to you, it would override the straight-hair gene you inevitably got from your father.
But now imagine that the straight hair gene prevented the development of eggs carrying a copy of curly hair. All of her children would inherit straight hair genes only, and have straight hair. This is what biologists term a “selfish gene.”
An advantage to a gene like this, which spreads quickly, is that it may offer a benefit such as disease resistance. Many organisms, including some house mice, have naturally occurring selfish genes, or “gene drives,” but they tend to be species that reproduce quickly.
For house mice with the gene drive, the drive affects the normal wild sperm, allowing only those with the drive to fertilize an egg. Think of it like “sperm wars”; mice that carry the drive spread the gene down to greater than 95 percent of their offspring. Now if this drive can also carry the gene that determines whether an embryo develops testes, this will bias inheritance and the majority of the offspring born should be male.
Gene drive systems have been proposed for eradicating insects, such as mosquitoes and other invertebrates but this is the first attempt in a vertebrate that has its own gene drive. While these models are focused on invertebrates, they are similar in scope and we can use aspects from these models to try and predict if this would be a worthwhile endeavor.
As a radically new idea, the use of genetically modified mice for island pest management is still in very early stages of testing. Many questions must still be answered through diligent research, especially regarding key differences between wild and genetically modified mouse populations. The success of this idea depends heavily on the genetically modified male mice being “studs” with the island lady mice. If given a choice, will these females pick the local guy next door or the stranger with some lab mouse in his background? Will it matter that island mice can typically jump faster and are more aggressive than lab mice? Will she want a hybrid male that is part wild, part lab? After all, releasing more modified mice won’t help if the females don’t want to mate with the newcomers.
There are now several universities and different groups working with Island Conservation to test the potential of eradicating invasive rodents from islands with gene drives. While the technology is only at the beginning stages, it may hold the potential to be mouse-specific, and prevent island wildlife from going extinct.