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

After it was nearly extinct, the entire genome of the endangered Převalsky’s horse was mapped by a team from the University of Minnesota.

A team of researchers reports that they have mapped the complete genome of the endangered Převalský horse, Equus ferus przewalskii. Once extinct in the wild, today, thanks to various conservation efforts, approximately 2,000 individuals of this species live in both captive populations and reintroduced herds.

Převalský’s horse was almost exterminated

The Przewalski’s horse, also known as the Asian wild horse, Mongolian wild horse, or Dzungar wild horse, is an endangered species originally native to the high-altitude grass steppes of central Eurasia. Historically, these horses were the subject of many Mongolian folk tales and were recognized as steeds ridden by the gods, so the Mongols named them “takhi”, which translates to “spirit” or “holy”.

These horses were decimated in the wild by livestock grazing and agricultural competition, as well as other human conflicts and harsh winter conditions—and in fact, they were almost completely exterminated. Between 1899 and 1902, an animal dealer and several large landowners captured a large number of wild foals to establish a captive breeding program. Sadly, only 53 survived the rough journey from Mongolia to Europe. After they arrived, the foals were dispersed to a number of zoos and private parks. All of today’s Převalský horses in captivity are descendants of only 13 of these ancestors who produced offspring.

A formal breeding program was started in 1959, but unfortunately even then there was not much official policy governing the exchange of Przewalski horses between zoos and private parks until 1980. This led to a high level of inbreeding, which led to the spread of various genetic diseases throughout the population. The average life span of the takhi has been greatly reduced and foal mortality has increased. Few of Převalský’s purebred mares could give birth alive.

In addition to captive breeding programs, numerous conservation efforts have been initiated for the species, including reintroduction and monitoring systems, protection of native wild horse territories, and cloning. As a result, takhi were listed as Extinct in the Wild to Critically Endangered in 2008 and then to Endangered in 2011.

Although some experts consider the takhi to be a subspecies of an extinct species Equus ferus, a wild horse from which domestic horses are probably descended, others think the takhi are their own species. There is some precedent for this position. For example, the takhi has 33 pairs of chromosomes, compared to the 32 found in domestic horses. Moreover, their lineages diverged from a common ancestor between 160,000 and 38,000 years ago—long before the horse was domesticated. This means that takhi can produce fertile hybrids when bred with domestic horses – a situation that has been used to slightly alleviate their severe inbreeding problems by introducing a small number of domestic horses into the takhi gene pool.

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

The takhi genome has been sequenced using state-of-the-art technology

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

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

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

Professor Faulk and his collaborators used the Oxford Nanopore sequencing device, a small, pocket-sized cutting-edge technology to reconstruct the complete horse genome. This small device is almost the equivalent of those gigantic machines used for DNA sequencing, with almost the same capacity. The resulting takhi sequence data was then built onto the scaffold of the domestic horse reference genome.

In my opinion, probably the most interesting aspect of this particular technology is its portability, which could allow it to be adapted for further study of wild Przewalski’s horses (or any other creature, really) in remote locations.

The Převalské horse genome is a critically important contribution to their conservation

The takhi genome is a critically important contribution to the conservation and continued survival of these rare horses: scientists are now using it to make predictions about what different gene mutations might 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 a picture on the box,” noted the study’s lead author, veterinary bioinformatics researcher Nicole Flack, who is in the University of Minnesota’s College of Veterinary Sciences. “Przewalski’s horse researchers studying mutations in an important gene need a good reference image to compare their puzzle to.”

Now that the structure of the horse’s genome is known, future applications may include studying the genes that help these animals adapt to environmental changes, identifying mutations associated with specific traits or diseases, and informing future breeding decisions to help preserve the genetic diversity of the population. Given the extreme population decline that has occurred as a result of the near extinction of these horses, this information is critical to the continued success of conservation 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 Zoo Minnesota.

“We are excited to offer our community the opportunity to see horses as the results 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 the Przewalski horse (Equus ferus przewalskii), G3 genes|genomes|genetics, jkae113 | doi:10.1093/g3journal/jkae113

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