The genome of the last living wild horse species has now been mapped

After it nearly became extinct, the entire genome of an endangered Przewalski’s horse has been sequenced by a team at the University of Minnesota

A team of researchers reports they have sequenced the entire genome of the endangered Przewalski’s horse. Equus ferus przewalskii. Once extinct in the wild, approximately 2,000 individuals of this species now live in both captive populations and reintroduced herds, thanks to a variety of conservation efforts.

Przewalski’s horse almost became extinct

Przewalski’s horse, also known as the Asiatic wild horse, the Mongolian wild horse or the Dzungarian wild horse, is an endangered species originally native to the high-altitude grassy steppes of Central Eurasia. Historically, these horses were the subject of many Mongolian folk tales and were recognized as the horses ridden by the gods. That’s why the Mongols called them ‘takhi’, which translates to ‘spirit’ or ‘sacred’.

These horses became extinct in the wild due to livestock grazing and agricultural competition, as well as other human conflicts and brutal winter conditions – in fact, they were almost completely wiped out. Between 1899 and 1902, an animal dealer and several landowners captured a large number of wild foals so they could establish a captive breeding program. Unfortunately, only 53 survived the arduous journey from Mongolia to Europe. After they arrived, the foals were distributed to a number of zoos and private parks. All contemporary Przewalski’s horses in captivity are descendants of only 13 of these ancestors who produced offspring.

A formal breeding program was initiated in 1959, but unfortunately even then there was not much official policy for the exchange of Przewalski’s horses between zoos and private parks until 1980. This resulted in a high degree of inbreeding, leading to the proliferation of Przewalski’s horses. a variety of genetic diseases throughout the population. The average lifespan of the takhi was significantly shortened and foal mortality increased. Few purebred Przewalski mares can give birth live.

In addition to captive breeding programs, several conservation efforts have been made to preserve the species, including reintroduction and monitoring systems, protecting the wild horses’ breeding grounds and cloning. As a result, takhi was downlisted from Extinct in the Wild to Critically Endangered in 2008, and then to Endangered in 2011.

Although some experts consider takhi to be a subspecies of the extinct Equus ferus, the wild horse from which domesticated horses are likely descended, others think takhi is their own species. There is precedent for this argument. For example, Takhi has 33 chromosome pairs, compared to 32 in domestic horses. Furthermore, their ancestors split from a common ancestor between 160,000 and 38,000 years ago – long before the horse was domesticated. That said, takhi can produce fertile hybrids when bred with domestic horses – a situation that was used to somewhat alleviate their severe inbreeding problems by introducing a small number of domestic horses into the takhi gene pool.

Currently, the taxonomy of takhi remains controversial, and there is no consensus as to whether it is a complete species, a subspecies of the wild horse (alongside two other subspecies, the domestic horse and the extinct tarpan), or possibly even a subpopulation of the takhi. domestic horse.

The takhi genome was sequenced using an advanced technology

The blood sample used to construct a representative gene map for the species was provided by Varuschka, a 10-year-old captive-bred mare living at the Minnesota Zoo. The zoo has long been active in Przewalski’s horse breeding and management, with more than 50 foals born since the 1970s, and they have also contributed a stallion to the reintroduction efforts in Mongolia’s Hustai National Park, a project that started in 1992. Additional herds have since been reintroduced. in China, Hungary, Kazakhstan and Russia.

What is a genome? What can we learn by studying it?

“The genome is the basic blueprint for an animal and tells us what makes a species unique and also tells us about the health of a population,” said the study’s senior author, molecular biologist Christopher Faulk, associate professor of Food, Agricultural and Natural. Resource Sciences at the University of Minnesota. Professor Faulk is an expert in evolutionary genomics, molecular genetics and bioinformatics.

“My students worked together to produce the highest quality Przewalski horse genome in the world,” added Professor Faulk. The students who contributed to sequencing the takhi genome were enrolled in Professor Faulk’s animal science course.

Professor Faulk and his collaborators used Oxford Nanopore sequencing devices, a small, advanced, pocket-sized technology to reconstruct the horse’s entire genome. This small device is almost the functional equivalent of the gigantic machines used for DNA sequencing, with virtually the same capacity. The resulting takhi sequence data was then reconstructed on a domestic horse reference genome scaffold.

In my opinion, probably the most interesting aspect of nanotechnology is its portability, which allows it to be adapted for further studies of wild Przewalski’s horses (or any other beast) in remote locations.

Przewalski’s horse genome makes a crucial contribution to its conservation

The takhi genome makes a crucial contribution to the conservation and survival of these rare horses: researchers are now using it to make predictions about what different gene mutations could mean for the health and conservation of these endangered horses.

“Studying genes without a good reference is like putting together a 3 billion-piece puzzle without the picture on the box,” said the study’s lead author, veterinary bioinformatics researcher Nicole Flack, of the College for veterinary medicine from the University of Minnesota. “Przewalski’s equine researchers studying mutations in an important gene need a good reference image to compare their puzzle to.”

Now that the horse’s genome structure is known, future applications could include studying genes that help these animals adapt to changes in the environment, identifying mutations associated with specific traits or diseases, and informing future breeding decisions to help maintain the declining genetic diversity of the population. Given the extreme population bottleneck that occurred as a result of the near extinction of these horses, this information is critical to the continued success of conservation breeding efforts.

“We were excited to work with the University of Minnesota to preserve the genetic health of the species as their populations continue to recover, both in zoos and in the wild,” said study co-author Anne Rivas, a doctor of veterinary medicine at the Minnesota Zoo.

“We are pleased to offer our community the opportunity to see the horse as a result of our conservation efforts.”

Source:

Nicole Flack, Lauren Hughes, Jacob Cassens, Maya Enriquez, Samrawit Gebeyehu, Mohammed Alshagawi, Jason Hatfield, Anna Kauffman, Baylor Brown, Caitlin Klaeui, Islam F Mabrouk, Carrie Walls, Taylor Yeater, Anne Rivas and Christopher Faulk (2024). The genome of Przewalski’s horse (Equus ferus przewalskii), G3 genes|genomes|genetics, jkae113 | doi:10.1093/g3journal/jkae113

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