How Genetic Rescue Works

continuum of wildlife facing genetic predicaments is represented in this diagram – matched with a continuum of genetic rescue techniques being developed and applied by Revive & Restore.  The species shown from left to right are in increasing danger of extinction (red arrows).  Genetic rescue can head them back to the left, away from extinction (green arrows).  For details on each species, roll over the plus signs.

Genetic Rescue Continuum Revive & Restore
Northern White Rhinoceros: Only 3 individuals of this species survive, all too old to breed. San Diego Zoo Global is leading the effort to use stem cell embryogenesis to give birth to a new generation of Northern White Rhinoceros, using a dozen frozen cell lines as the source for a new founding population.
Passenger Pigeon: The passenger pigeon served as an ecosystem engineer creating forest regeneration cycles in eastern North America for tens of thousands of years. Today many species are in decline without regenerating habitat types. The return of this species’ ecological function will not only save species, but improve the bioproductivity of forests for humans as well.
Genetic analysis revealed that the 9 subspecies (distinguished by unique color patterns) are in fact 4 distinct species, several of which exist in the wild in very low numbers. The four distinct subspecies of the Northern Giraffe number less than 5,000 altogether, ~5% of all Giraffe species combined. Biobanking cell lines can preserve the genetic diversity that remains in case of further losses.
Woolly Mammoth: The Woolly Mammoth’s grassland ecosystem was a major contributor to climate stability over the past 130,000 years until human activities altered the landscape. Bringing back this ecosystem, by restoring grazing megafauna including the mammoth, may provide similar long-term stability to rapid human-driven climate change. Genome editing elephant cells to be more mammoth-like is already underway.
Przewalski’s Horse: The last wild horse species in the world was saved by a captive breeding program that increased the population from just 14 individuals to 1,800 over a period of 30 years. Cloning from historic cell lines could infuse lost genetic diversity into the population, improving long-term viability of its recovery in the wild.
Black-Footed Ferret: Once thought to be extinct, a remnant population of Black-footed Ferrets was discovered in 1981. Captive breeding has reared >9,000 ferrets from just 7 founders over 35 years to save the species, but disease threatens its long-term recovery. Genetic rescue can help.
Hawaiian Honeycreeper: Nearly half of Hawaii’s unique honeycreeper species died out due to human activities. Avian malaria spread by invasive mosquitoes threatens the remaining species with extinction. Genomic technologies have the potential to eradicate mosquitoes safely and eliminate the disease.
Arabian Oryx: This species of antelope became extinct in the wild in 1972. Since then, captive breeding efforts have successfully reintroduced herds to five countries so far, with more reintroductions planned. Wild populations of the Arabian Oryx are stable, and captive populations ensure the survival of the species, thus demonstrating the high value of intervening with a species in trouble.
Peregrine Falcon: Pesticides and habitat problems caused the Peregrine Falcon to disappear from eastern North America. A hybrid of Peregrine Falcon subspecies was introduced, and today falcons thrive in urban settings. Genetic insight and the de-extinction of the Passenger Pigeon may help Peregrines recover in wilderness habitats.
Giant Tortoises: Tortoises are important ecosystem engineers, and have been the face of many successful island conservation innovations on the Galapagos, Mauritius and Hawaii.
California Condor: This is the premiere example of a conservation program that successfully applied genetic insight to population management and recovery. By the late 1980s, a declining population had left the California Condor with only 27 individuals and an extreme genetic bottleneck from which the bird is still slowly recovering. Whole genome sequences are guiding captive breeding to preserve diversity and prevent the spread of a lethal genetic disorder. The success of captive breeding has led to the conservation of nearly one million acres of Condor habitats as well.
American Chestnut Tree: Once the dominant tree of eastern U.S. forests, this tree was nearly wiped out by introduced Asian fungal blight, which prevents trees from recolonizing >95% of their range. Scientists have engineered complete immunity to Asian blight into the tree’s genome using a single gene from wheat. With regulatory approval, American chestnut is poised to make a big comeback, and it could be the first example of genetic engineering’s ability to save a species.
Bats: The fungal disease White-Nose Syndrome has spread from just one cave to 33 states and 3 provinces in the U.S. and Canada in just 11 years, killing as many as 90 to 100% of hibernating bat colonies in some states. Genetic intervention focused on either the fungus or the bats may provide solutions to this disease.
Frogs: Over the past 30 years, chytrid fungus has caused population decline and the extinction of almost 200 species of frogs. Some types of bacteria provide anti-fungal protection and some species appear to be resistant to the disease. Genetic rescue efforts could use these discoveries to save vulnerable species.
Micronesian Kingfisher: This bird has lived in captivity in zoos for over 30 years, unable to return to its native habitat on Guam because of invasive Brown Tree Snakes. The recovery of this species depends upon the development of genomic management, like the California Condor program, as well as genetic solutions to eradicate snakes from Guam
Alagoas Curassow: A relative of turkeys and chickens, this species’ captive population of 130 birds could be greatly expanded with reproductive technologies, using primordial germ cell culturing and interspecies germ-line transmission. With greater numbers, the species could be restored to the wild. Germ-cell cultures would also ensure the preservation of the species’ genetic diversity.
Heath Hen: Revive & Restore’s genetic analysis shows the Heath Hen, a type of Prairie chicken, was a unique species. The revival of its unique genetic traits will not only allow the restoration of booming birds to New England, but also offer ways of conserving Prairie Chicken populations throughout the midwest. Thriving Prairie Chickens indicate a healthy landscape for many more species.
Great Auk: The Great Auk is a good candidate for de-extinction. Its genome has been sequenced; it has a close living relative; and, its habitat is intact. The return of this iconic “penguin of the north” could compel sustainable fishing activities and enrich the ecological dynamics of Atlantic seabirds.
Aurochs: The Aurochs was once widespread throughout Eurasia, keeping meadow habitats open by browsing on tree saplings. Rewilding efforts in Europe are currently working to back-breed living cattle varieties, all descended from extinct Aurochs, in order to generate a breed of cattle capable of resuming the wild habitat role of the extinct species.
Asian Elephant – In recent decades, a lethal strain of herpes has been killing young Asian elephants both in the wild and in captivity, threatening the existence of an already vulnerable species. The Church Lab at Harvard Medical School is using synthetic biology to reconstruct a lab-grown form of the virus in order to develop a treatment and possibly a genetic rescue solution.

Genomics and emerging biotechnologies are reshaping the field of genetic rescue. Historically, genetic rescue relied on introducing new individuals from distant ranges to save an isolated population suffering from inbreeding depression, a consequence of low genetic diversity resulting from a population bottleneck. A famous example is the case of the Florida Panther. By 1995 there were fewer than thirty panthers, resulting from a severe bottleneck of only six founding individuals. Odd physical traits began to appear and fertility and reproduction declined. To save the population, eight female Texas Cougars were introduced to Florida to hybridize, creating new genetic diversity. The population immediately grew, and today numbers more than 100 panthers, the carrying capacity for their habitat range. Increasing genetic diversity saved the Florida Panther’s resilience and adaptability. Resilience through genetics is the core theme at the heart of the modern reformation of genetic rescue approaches.

Today’s genomic technologies offer a broader suite of methods to increase genetic diversity rather than relying solely on physically translocating animals. In fact, the most advanced technologies will help to address very significant but specific concerns.

How Genetic Rescue Works

Rapid advances in genomics are expanding how genetic insight can inform the conservation of isolated populations to entire ecosystems. These new technologies are providing powerful new tools to advance conservation — from new genomic-based insights to more advanced interventions that address vexing conservation problems.

For instance, advanced reproductive technologies and genome editing are now making it possible to use genetic insight to address threats and save species in ways never before possible. Longer term, there is even an opportunity to restore the ecological function of extinct species with living adapted proxies, a process known as de-extinction. While biotechnology are enables new tools for genetic rescue, the practices and strategies are rooted in proven innovative conservation efforts: translocation, captive breeding, assisted reproduction (such as artificial insemination), adaptive conditioning, reintroduction, and ecological replacement.

The diagram above displays a range of threatened and endangered wildlife facing different challenges on the continuum towards extinction (red arrows) and the genetic rescue techniques that can aid recovery (green arrows). The wildlife depicted all present specific examples that either outline the genetic rescue tools that can be applied to save threatened wildlife and/or innovations already yielding recovery. The goal of all genetic rescue projects is to move species from the right of the continuum to the far left.  Genetic rescue should complement traditional and important forms of conservation like the protection of habitat and the control of invasive species.