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

After it nearly went extinct, the complete genome of an endangered Przewalski’s horse was mapped by a team at the University of Minnesota.

A team of researchers reports having mapped the complete genome of the endangered Przewalski’s horse, Equus ferus przewalskii. Once extinct in the wild, there are now approximately 2,000 individuals of this species living today in captive populations and reintroduced herds, thanks to various conservation efforts.

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Przewalski’s horse almost disappeared

The Przewalski’s horse, also known as the Asian wild horse, Mongolian wild horse or Dzungarian wild horse, is an endangered species 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. This is why the Mongols named them “takhi,” meaning “spirit” or “holy.”

These horses became extinct in the wild due to livestock grazing and agricultural competition as well as other human conflicts and brutal winter conditions – and in fact, they were almost entirely wiped out. Between 1899 and 1902, a pet trader and several large landowners captured large numbers of wild foals in order to establish a captive breeding program. Unfortunately, only 53 survived the arduous journey from Mongolia to Europe. After their arrival, the foals were dispersed to several zoos and private parks. All Przewalski horses in captivity today 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 no real official policy governing the exchange of Przewalski horses between zoos and private parks until 1980. This led to high levels of inbreeding, which led to the proliferation of Przewalski’s horses. a variety of genetic diseases in the population. The average lifespan of the takhi was significantly shortened and foal mortality increased. Few purebred Przewalski mares could give birth to live animals.

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In addition to captive breeding programs, multiple conservation efforts have been initiated to preserve the species, including reintroduction and monitoring systems, protection of wild horses’ native lands, and cloning. As a result, takhi were reclassified from Extinct in the Wild to Critically Endangered in 2008 and then Endangered in 2011.

Although some experts consider the takhi a subspecies of the extinct species A wild horse, the wild horse from which domestic horses are likely descended, others believe that takhi are their own species. There is precedent for this position. For example, takhi have 33 pairs of chromosomes, compared to 32 in domestic horses. Additionally, their ancestral lines 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 crossed with domestic horses – a situation that has been used to slightly alleviate their serious inbreeding problems by introducing small numbers of domestic horses into the takhi gene pool.

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

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The Takhi genome was sequenced using cutting-edge technology

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

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

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

Professor Faulk and colleagues used Oxford Nanopore sequencing devices, a small, cutting-edge technology, to reconstruct the complete horse genome. This small device is almost the equivalent of these gigantic machines used for DNA sequencing, with almost the same capacity. The resulting takhi sequence data were then constructed on a domestic horse reference genomic scaffold.

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, in fact) in locations distant.

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Przewalski’s 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: researchers are now using it to make predictions about what various genetic mutations might mean for the health and conservation of these endangered horses.

“Studying genes without a good reference is like doing a 3 billion piece puzzle without the picture on the box,” noted the study’s lead author, veterinary bioinformatics researcher Nicole Flack, who works at the University of Minnesota College of Veterinary Sciences. “Przewalski’s equine researchers studying mutations in an important gene need a good reference image with which to compare their puzzle.”

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Now that the structure of the horse genome is known, future applications could include studying genes that help these animals adapt to environmental changes, identifying mutations associated with specific traits or diseases, and information on future breeding decisions to help maintain the genetic diversity of the population. Given the extreme population bottleneck resulting from the near extinction of these horses, this information is critical to the continued success of conservation breeding efforts.

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

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

Source:

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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 Przewalski horse genome (Equus ferus przewalskii), G3 Genes|Genomes|Genetics, jkae113 | doi:10.1093/g3journal/jkae113

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