Earth's biodiversity is in crisis. An imminent "sixth mass extinction" threatens beloved and important wildlife. It also threatens to reduce the amount of genetic diversity - or variation - within species.
Author
- Cock Van Oosterhout
Professor of Evolutionary Genetics, University of East Anglia
This variation in genes within a species is crucial for their ability to adapt to changes in the environment or resist diseases. Genetic variation is therefore crucial for species' long term survival.
Traditional conservation efforts - such as protected areas, measures to prevent poaching, and captive breeding - remain essential to prevent extinction. But even when these measures succeed in boosting population numbers, they cannot recover genetic diversity that has already been lost. The loss of a unique gene variant can take thousands of years of evolution before it is recovered by a lucky mutation.
In a new paper in Nature Reviews Biodiversity, an international team of geneticists and wildlife biologists argues that the survival of some species will depend on gene editing, along with more traditional conservation actions. Using these advanced genetic tools, like those already revolutionising agriculture and medicine, can give endangered species a boost by adding genetic diversity that isn't there.
Genetic engineering is not new. Plant breeders have used it for decades to develop crops with traits to boost disease resistance and drought tolerance. Around 13.5% of the world's arable land grows genetically modified crops . Gene-editing tools such as Crispr are also being used in "de-extinction" projects that aim to recreate extinct animals.
The Dallas-based company Colossal Laboratory & Biosciences has attracted headlines for its efforts to bring back the woolly mammoth, dodo and dire wolf. In de-extinction, the DNA of a living relative species is edited (changed) to approximate the extinct species' most charismatic traits.
For example, to "resurrect" a woolly mammoth , Colossal's researchers plan to splice mammoth genes (recovered from ancient remains) into the genome of the Asian elephant to produce a cold-hardy, hairy elephant-mammoth hybrid. Colossal recently engineered grey wolf pups with 20 gene edits from the extinct dire wolf's DNA.
The "Jurassic Park"-style revival of long-gone creatures has attracted considerable attention and funding, which has accelerated the development of genome engineering techniques. These same genome editing tools can be used for conservation of existing and endangered species. If we can edit a mouse to have mammoth hair, or edit a wolf to resemble a dire wolf, why not edit an endangered bird's genome to make it more resilient to disease and climate change?
Museum specimens
Using DNA from historical specimens, scientists can identify important genetic variants that a species has lost. Many museums hold century-old skins, bones, or seeds - a genomic time capsule of past diversity. With genome editing, it is possible to reintroduce these lost variants into the wild gene pool.
By restoring genetic variation, species can be fortified against emerging diseases and environmental change. A sharp decline in population numbers is called a "bottleneck" . During a bottleneck, inbreeding and genetic drift lead to the random loss of genetic diversity. Harmful mutations can also increase in frequency. Such "genomic erosion" compromises the health of individuals and can make populations more prone to extinction.
If we can pinpoint a particularly damaging mutation that has become widespread in the population or a variant that has been lost, we could replace it in a few individuals using gene editing. Aided by natural selection, the healthy variant would gradually spread in the population.
If a threatened species lacks genes that it desperately needs to survive new conditions, why not borrow them from a close relative that already has those traits? Known as facilitated adaptation , this could help wildlife cope with threats such as climate change.
In agriculture, such cross-species gene transfers are routine. Tomatoes have been engineered with a mustard plant gene to tolerate cold, and chestnut trees got a wheat gene for disease resistance. There is no reason why such techniques cannot be expanded to animals.
These genetic interventions can complement, but never replace traditional conservation measures. Habitat protection, control of invasive predators, captive breeding programmes, and other on-the-ground action remain absolutely necessary. Importantly, gene editing only makes sense if the target population has recovered in numbers enough (often through conservation), to allow natural selection to do its job.
Measuring the risk of extinction
Gene-edited animals or plants wouldn't have a chance if released into a barren habitat or a poaching hotspot. Genomic tools can give an extra edge to species that are already being saved from immediate threats, equipping them for adaptive evolution in the future.
Climate zones are shifting, new diseases are spreading, and once-isolated populations are cut off in small fragments of habitat. Without intervention, even intensive habitat management might not prevent a wave of extinctions.
However, a strategy of gene editing also comes with significant risks and unknowns. One technical concern is off-target effects - Crispr and other gene-editing techniques might make unintended DNA changes in addition to the intended edit. In other words, you attempt to insert a disease-resistance gene, but accidentally disrupt another gene in the process. Similarly, a gene may have more than one function, which is known as pleiotropy.
Especially in less-well studied species, we may not be aware of all those functions or pleiotropic effects. Regulatory inertia and public scepticism may also present big obstacles - these issues have historically limited the rollout of genetically modified (GM) organisms, particularly in agriculture.
There are also evolutionary and ecological uncertainties. A deliberate gene edit might have knock-on effects on how the species evolves over time. For instance, if one individual is given a highly beneficial gene that spreads rapidly, it could replace all the other gene variants at that location in the genome (the full complement of DNA in the organism's cell). This is known as a "selective sweep", and it inadvertently reduces the genetic diversity in that region of the genome.
Some critics argue that the narrative of a genetic quick fix could distract from the root causes of biodiversity loss. If people believe we can simply "edit" a species to save it, will that undermine the urgency to protect habitats or cut carbon emissions? Portraying extinction as reversible might seed false hope and reduce the motivation for tough environmental action.
Conservation efforts, strong environmental policies and legal protections remain indispensable. So do habitat restoration, climate action and reducing the impact made on the environment by humans.
Nevertheless, genome engineering is a new tool in the conservation toolbox. It's one that -given the right assistance and environmental encouragement - can help save species from extinction.
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Cock Van Oosterhout receives funding from the Royal Society for conservation genomics work on threatened bird species in Mauritius, and a donation by the Colossal Foundation for conservation genomic research on the pink pigeon. He is member of the Conservation Genetics Specialist Group of the IUCN (International Union for Conservation of Nature).
