Past, present and future of an endangered species: the Przewalski’s horse.

          Przewalski’s horses, Equus ferus przewalskii, are the only true wild horses currently remaining on Earth. In contrast to feral horses, which actually represent the descent of domesticated animals that returned to the wild, the Przewalski’s horse has never been domesticated because of its temper. This iconic horse is endangered, but survives thanks to massive conservation efforts. Ensuring its future survival is essential as it represents not only a unique biodiversity resource but also a great opportunity for scientific research.

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A Przewalski’s horse in Mongolia. Credit: National Geographic

A bit of history

Native of Mongolia, The Przewalski’s horse has been discovered in the late 1870s in Central Asia, during an expedition led by Colonel NikolaiPrzewalski1. He was then the first to describe this extraordinary horse in 1881. Massive and robust, with short dark legs, a pale coat and an erected mane, the Przewalski’s horse attracted Western Europe2. As such, many individuals were captured in the early 1900s and brought to zoos in Europe. But, as capturing adults was difficult because they were fast and very aggressive, only foals were brought to European zoos. The four expeditions led in the early 1900s managed to bring to Europe only 53 foals and implied massive killings of adults in herds. At the same time, the success of domestic livestock in the Asian steppes, combined with over-hunting and the succession of several harsh winters, created huge pressures on the wild horses. These factors led to a dramatic decline of the population in only a few decades. The last wild individual was captured alive in 1947 and the population became eventually extinct in the wild–the last specimen having been seen in the wild in 1969.

A Przewalski’s foal captured and brought to the Munich Zoo. Credit: Neumeister

As the horse population was declining in the wild, a captive stock was growing in western zoos. Of the 53 captured, only twelve foals reproduced resulting in a rapid decline in the population held in captivity as they were down to 31 individuals at the end of World War II.However, thanks to important conservation efforts, including the First International Symposium on the Preservation of the Przewalski’s Horse in 1959, the captive population eventually increased. By 1979, 385 individuals were bred in captivity. In 1985, reintroduction projects started throughout Europe and inside their historic range, in Mongolia and China3.

Reintroductions into the wild

When reintroductions began, the whole population of Przewalski’s horses represented the descent of a limited founding population of 13 individuals. This pool includes 12 founders brought from Central Asia – one being a hybrid born to a captured stallion and a domestic Mongolian mare – and the last individual caught later, in 1947. Such a drastic demographic bottleneck implied high levels of related inbreeding, associated with shorter lifespan and increased juvenile mortality. Therefore, only a careful management of horses could allow the survival of the population in the wild. Since the first reintroduction action, all horses were given identification numbers written on ear labels associated to a World Studbook of Przewalski’s horses that contains for each individual the identity of the parents and the date and place of birth. This allowed conservationists to know the identity of each horse and has been determinant in deciding where and with whom each individual should be reintroduced in order to keep the inbreeding levels as low as possible: the less related horses are, the better it is. Identifying each individual has also led to an increased understanding of the demographic characteristics of each population, including reproductive and fertility rates. This has been particularly important in ensuring good health of foals at the beginning, when reintroduced populations were very small and hence extremely fragile.

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The six main reintroduction sites of the Przewalski’s horse in Central Asia. Credit: yalakom.org

 

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A Przewalski’s horse during the winter, in Western Mongolia. Credit: Claudia Feh

Tracking the movement of each reintroduced group has also been decisive in the reintroduction actions. For instance, knowing precisely where the horses were going led to actions to prevent horses living in the Kalamaii nature reserve (China) from going too far North during each winter4. Harsh climatic conditions combined with competition with other species could have been fatal to the Przewalski’s population. Besides, correlations between location of reintroductions and their success revealed which projects were the most successful and thus what were the most favourable conditions for reintroductions. In the end, most reintroduction projects were successful, and today, the global population of Przewalski’shorses counts approximately 1,900 individuals in zoos and reintroduction reserves.

 

Why are Przewalski’s horses so important?

Since the extinction of the Przewalski’s population in the wild many decades ago, little is known about the social structure of them. Recent research showed that all females live in harems where one dominating stallion mates with all mares of the group, while most males gather in bachelor groups. Future investigations on the structure and behaviour will undoubtedly provide relevant insights about how horses could have behaved in the early stages of horse domestication. Comparing wild animals to the diversity of domestic breeds known offers an unprecedented opportunity to dissect the domestication, a process that has been of major importance in human history for agriculture, warfare and for the expansion of nomad empires, such as Huns and Mongols.

Furthermore, recent genetic research based on the sequencing of the first complete genome of a Przewalski’s horse have revealed comparable levels of genetic diversity in Przewalski’s horses and domestic breeds. This result is very encouraging as it shows that despite its impressive related inbreeding, the population is likely genetically sustainable and might actually not be doomed in the long term by its consanguinity.

In any case, all scientific results plead for the uniqueness and preservation of Przewalski’s horse and invites for a larger characterization of the genetic pool of this animal, which is plentiful of variants that do not exist in the domestic livestock5. Even though genetic studies are encouraging as regards its future survival, it is essential to pursue the conservation efforts with a very careful management to keep inbreeding under control. After all, the population represents our unique chance to understand the process of domestication and hence our own history!

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A herd of Przewalski’s horses in the Gobi Desert. Credit: horsejournals.com

 

References

  1. Boyd L. & Houpt K. 1994. Przewalski’s Horse : The History and Biology of an Endangered Species, Suny Series
  2. Zimmermann, W. 2005. Przewalski’s horses on the track to reintroduction – various projects compared. Zeitschrift des Kolner Zoo 48 (4), pp.183-209.
  3. Moehlman, P.D., 2002. Equids: Zebras, Asses and Horses. Status Survey and Conservation Action Plan, 82-90
  4. Xia, C. et al., 2014. Reintroduction of Przewalski’s horse (Equus ferus przewalskii) in Xinjiang, China: The status and experience. Biological Conservation, 177, pp.142–147.
  5. Bowling, A.T. et al., 2003. Genetic variation in Przewalski’s horses, with special focus on the last wild caught mare, 231 Orlitza III. Cytogenetic and Genome Research, 102, pp.226–234.
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