What a Cloned Ferret Means for Species Conservation
The preservation of endangered species is an uphill battle against the seemingly insurmountable effects of climate change and careless human intervention. According to WWF’s 2020 Living Planet Report, the population sizes of mammals, fish, birds, amphibians, and reptiles have declined on average by 68% since 1970. Listed culprits include overexploitation, pollution, climate change, and the inadvertent introduction of invasive species and diseases. Without extensive efforts to oppose habitat loss and deterioration, the downward trend will continue unmitigated. The current pandemic has muddled both short and long-term goals in the field, as wildlife protection operations have suffered dramatic budgetary losses in the absence of tourism and with the redirection of donors and state funding.
But looking through the fog of grim news, one might catch a glimpse of optimism. On December 10th, the currently endangered black-footed ferret species welcomed a novel addition: a clone kit named Elizabeth Ann. The small ferret shares its DNA with a long-deceased wild one, Willa, whose genetic makeup has been preserved as skin cells in San Diego’s Frozen Zoo since the mid-1980s. The feat is not a first for the team behind it, a collaboration between Revive & Restore, the U.S. Fish and Wildlife Service, ViaGen Pets & Equine, the San Diego Zoo Global, and the Association of Zoos and Aquariums. In August 2020, they successfully cloned a Przewalski horse named Kurt.
How cloning works
Cloning occurs in nature when living organisms create a genetically identical offspring to themselves through asexual reproduction, and is wide spread amongst many types of bacteria and plants, such as blueberries. Whether polyembryony, when multiple embryos develop from the same fertilized egg, is considered cloning is still debated in the scientific community. The offspring are nearly genetically indistinguishable from one another , but not from their parents. Identical twins occur fairly rarely in humans, whereas other vertebrates rely on it constantly: the nine-banded armadillo, for example, always gives birth to identical quadruplets.
Although splitting embryos in the lab has been routinely achieved, artificial cloning of the kind performed to produce Elizabeth Ann is more complicated. It involves transferring DNA from somatic cells (meaning non-reproductive cells) to viable unfertilized eggs, a scientific process first performed in 1924 by Nobel laureate Hans Spemann and embryologist Hilde Mangolde. Scientists extracted Willa’s DNA from the skin cells cryopreserved at the Frozen Zoo, removed an egg from a live female ferret donor, and replaced the genetic material found in the egg with Willa’s. The process is called somatic cell nuclear transfer and was first successfully used in reproductive cloning in 1996, with the famed birth of Dolly the sheep.
The newly-modified egg developed into an early-stage embryo inside a test tube before being implanted into the womb of a surrogate mother. For the procedure to succeed, both the egg donor and the surrogate need to be of the same or of a close species to the intended clone, even if the resulting animal will only count the original stem cell donor as a parent. In Dolly’s case, all animals were of the exact same species. Both ferrets involved in Elizabeth Ann’s conception are domesticated ferrets, while the kit is fully a black-footed ferret, a first for cross-species reproductive cloning.
So are Willa and Elizabeth Ann the same ferret? Definitely not. Reproducing the genetic material does not equate with creating an exact copy. The way genes manifest is largely dependent on the environment, and that applies to the early stages of development as well. A clone grows in a different uterus and in different circumstances than its parent animal, so Elizabeth Ann would have not been identical to Willa even at birth.
Risks of cloning
Elizabeth Ann was born over two months ago at the Fish and Wildlife Conservation Center in Colorado, yet the press announcement was made on February 18th, as scientists often want to ensure the clone is healthy and adapting well before tooting any horns.
Cloning has proven to be a historically inefficient process with plenty of risks and failures. Dolly was the singular live lamb out of a total of 277 cloned embryos, while twin monkeys cloned in 2017 were the only successful attempts out of 21. The efficiency rate has significantly increased, but problems remain even after the first months of the cloned offspring’s life. Most reproductive cloning experiments conducted so far with mammals have resulted in health issues ranging from weakened immune systems to birth defects in vital organs such as the liver, heart, and brain. In 2003, a program attempted reviving an endangered species through 30 banteng clone pregnancies, out of which only half were successfully implanted and one alone made it to term. It resulted in twin calves, and while one was deemed healthy and raised in captivity, the other was euthanized days after birth due to its abnormal size.
Another problem worth discussing is the relative age of the chromosomes resulting from the initial somatic cells. The chromosomes’ endings, named telomeres, get shorter as the chromosomes divide over time, eventually preventing further division and triggering the death of the cell. While this is a natural occurrence in cell aging, taking an adult cell for the creation of an embryo might cut short the newly born animal’s life. Dolly was cloned using cells from a 6-year-old sheep and later died at six herself - the average sheep lifespan being twelve.
Elizabeth Ann’s tests show her in perfect health and she will continue to be monitored for most of her life. Although she will not be reintroduced into the wild, her offspring’s offspring should be eventually cleared for reintegration in three to four years, according to scientists at Revive & Restore.
Cloning for conservation
The success story brings much hope for the black-footed ferret, who faces the continued threat of the often-deadly sylvatic plague. All living ferrets of its kind are descendants of seven wild individuals, and are therefore closely related. As genetic diversity is strongly connected to pathogen resistance, such clones can help the species survive. Revive & Restore’s co-founder Ryan Phelan reports that Elizabeth Ann’s genetic information is three times more genetically diverse. “Reaching back into the past for the needed genetic diversity,” as she describes it, is a feasible alternative to genetic modification.
But it also invigorates the conversation around cloning as a means to aid dying species. The term used is “de-extinction,” and it describes the efforts to generate an organism belonging to a species declared extinct. While Jurassic Park-type projects are widely unattainable and undesirable, the more achievable feat of boosting the numbers of endangered species is palatable to the scientific community, as well as to the general public. San Diego Zoo Global’s Frozen Zoo has cryopreserved samples from approximately 1,100 rare and endangered species worldwide, opening an ample range of possible future projects.
Currently targeting coral reef for stem cell cloning and heath hen for reproductive cloning, Revive & Restore and their collaborators have also set their eyes on flagship species, such as the passenger pigeon and the woolly mammoth. They hope that the newly created ferret clone is proof of the initiative’s viability.
All things considered, efforts for de-extinction have only been made on a small scale and should not be confused for an alternative to established conservation efforts. Elizabeth Ann represents an astonishing triumph in preserving its kind, but cloning is not a realistic option for mass repopulation or for increasing biodiversity on a large scale. Conservationists have argued that the revival of dwindling species should not come at the cost of further endangering current ones. The question of which species would bring the most benefits to each ecosystem, and therefore be worth preserving or cloning, remains a difficult one to answer. But there is consensus on one point: before enthusiastically jumping at the prospect of positive human intervention, forceful and sustained efforts should be made towards lessening the damage we currently inflict.
