Cloning has only one hope of saving a lost breed of horses
This article is taken from Hakai Magazine, an online publication on science and society in coastal ecosystems. Read more stories like this on hakaimagazine.com.
Woman hopes technology can resuscitate Abaco Island’s now extinct horse breed, writes Stacey McKenna.
A horse named Nunki died in a forest in the Bahamas in July 2015, marking the end of the Abaco Island horse. But thanks to 21st century technology, extinction can be temporary. Two years later, Milanne Rehor, head of the Wild Horses of Abaco Preservation Society, received Bahamian government approval for an ambitious plan: use Nunki’s DNA and selective breeding to re-clone the breed.
How the horses got to the Abacos, an archipelago in the Bahamas, remains a mystery, but the herd’s roots can be traced back to the horses brought by Spanish explorers to the Americas 500 years ago.
In the 1960s, the population was around 200 until a child died trying to get on one of the horses. Residents responded by killing all but three. When Rehor arrived in 1992 – drawn to the islands by a love for the sea and a fascination with equines – the population had rebounded to 30 unstable individuals during evolution. Although numbers increased, genetic diversity had collapsed, leaving them vulnerable.
In 1999, Hurricane Floyd drove the pine horses to a citrus farm, where a diet loaded with pesticides caused toxins to build up in their bodies. No Abaco Island horse was born after 1999. Upon Nunki’s death, the breed was extinct. She had fallen ill after being treated with antibiotics for a cut.
“When you get to the point where there are no more living individuals of a species, cloning is your only chance,” says Katrin Hinrichs, veterinary physiologist and pharmacologist at Texas A&M University.
Cloning of extinct animals may work, even if this has its limits. Revive entire species like the woolly mammoth is still far away, and the only successfully resuscitated animal – a subspecies of ibex – died within minutes.
But Rehor and the Abaco Island Horse have a chance to change that. Equine cloning has high profile precedents, such as replication Twist Gem, a gelding and one of the greatest show jumping athletes. His clones – Gemini and Murka’s Gem – are now passing on his champion genetics to new generations.
Additionally, upon Nunki’s death in 2015, Rehor had the foresight to have a vet take tissue and send the sample to a Texas cloning lab, ViaGen. The technicians cultured the cells and then stored them cryogenically.
Almost every cell in a living animal contains a complete set of chromosomes from that animal – all the information needed to recreate the animal in its entirety. During normal fertilization, the oocyte halves its own chromosomes and the sperm provides the second half. When the sperm delivers its share, it triggers the egg to begin the process of becoming an embryo.
In cloning, you start with a mature, healthy egg from a donor mare. But instead of fertilizing that egg, you remove all of its chromosomes and replace them with the nucleus of the cell of the animal to be cloned – in this case, Nunki.
“Now you have an egg with two sets of chromosomes, as if it had been fertilized. You tell it it’s been fertilized and then it develops into an embryo, ”Hinrichs explains.
The embryo is cultured for about seven days until it can be considered viable, and then is transferred to a recipient mare. On average, only about 10 percent of cloned embryos develop normally. For every three people successfully transferred, two will give birth to a gestation and one to a live foal. The procedure is expensive, but ViaGen offered Rehor $ 2 million in pro bono work. Cloning is hardly guaranteed, but it is possible.
Hinrichs warns, however, that cloning won’t save the horse from Abaco Island in the long run. Perhaps this will bring Nunki back, but in order to revive the breed, cloned mares must breed.
“So that’s the puzzle. If you have to keep breeding with non-Abaco horses, eventually you’ll end up with a non-Abaco horse, ”she says.
Even if it is too late to revive a herd of pure horses from Abaco Island, it still helps to preserve Nunki’s genes.
Because clones keep genes alive and cloned horses can be introduced into herds to reproduce naturally, “cloning offers an incredible opportunity to improve the gene pool of species with limited genes,” Hinrichs explains. Saving Nunki’s genes could one day add outside genetics to a herd facing a bottleneck.
The precise benefits that the Abaco genes might confer are not known, says Gus Cothran, a veterinarian at Texas A&M University. However, when Cothran compared the DNA of the Abaco Island horse to a database of horse breeds, he found them historically significant and genetically unusual. Living on an island, the herd had preserved and amplified their Old World genes in a way few wild races have.
So, says Cothran, saving the genes is worth it. “It’s an insurance policy. You’re trying to keep something that you might need in the future, but you don’t know you need it yet.
Abaco Preservation Society Wild Horses