Przewalski's horse
Przewalski's horse, also called the takhi, Mongolian wild horse or Dzungarian horse, is a rare and endangered wild horse originally native to the steppes of Central Asia. It is named after the Russian geographer and explorer Nikolay Przhevalsky. Once extinct in the wild, since the 1990s it has been reintroduced to its native habitat in Mongolia in the Hustai National Park, Takhin Tal Nature Reserve, Khomiin Tal, and several other locales in Central Asia and Eastern Europe.
Several genetic characteristics of Przewalski's horse differ from those seen in modern domestic horses, indicating neither is an ancestor of the other. For example Przewalski's horse has 33 chromosome pairs compared with 32 for the domestic horse. Their ancestral lineages split from a common ancestor between 160,000 and 38,000 years ago, long before the domestication of the horse. Przewalski's horse was long considered the only remaining truly wild horse, in contrast with the American mustang and the Australian brumby, which are feral horses descended from domesticated animals. That status was called into question when domestic horses of the 5,000-year-old Botai culture of Central Asia were found to be more closely related to Przewalski's horses than to E. f. caballus. The study raised the possibility that modern Przewalski's horses could be the feral descendants of the domestic Botai horses. However, it remains possible that both the Botai horses and the modern Przewalski's horses descend separately from the same ancient wild Przewalski's horse population. Its taxonomic position is still debated, with some taxonomists treating Przewalski's horse as a species, E. przewalskii, others as a subspecies of wild horse or a variety of the domesticated horse.
Przewalski's horse is stockily built, smaller, and shorter than its domesticated relatives. Typical height is about, and the average weight is around. They have a dun coat with pangaré features and often have dark primitive markings.
Taxonomy
Przewalski's horse was formally described as a novel species in 1881 by Ivan Semyonovich Polyakov. The taxonomic position of Przewalski's horse remains controversial, and no consensus exists about whether it is a full species ; a subspecies of Equus ferus, the wild horse, ; or even a subpopulation of the domesticated horse. The American Society of Mammalogists considers both Przewalski's horse and the tarpan to be subspecies of Equus ferus and classifies the domesticated horse as a separate species, Equus caballus.Lineage
Genetic analysis shows that the takhi and the domesticated horse differ significantly, with neither ancestral to the other. The evolutionary divergence of the two populations was estimated to have occurred about 72,000–38,000 years ago, well before domestication, most likely due to climate, topography, or other environmental changes.According to a 2009 study, the earliest known domesticated horses were found at settlements of the Botai culture, from about 5500 years ago. These horses were raised for meat and milk. In 2018 a new study indicated ancient horses of the Botai culture are related to takhis, not to domesticated horses as was previously thought. Specifically, the Botai horses appeared to be ancestral to the modern takhi, because all seven takhis nested within the phylogenetic tree of the 20 Botai horses. No comparison was made to definitively wild early takhis. The authors posit that modern Przewalski's horses are feral descendants of the ancient Botai domesticated animals rather than representing a surviving population of never-domesticated horses. Another geneticist pointed out that Przewalski's horses may have simply descended from the same wild population that the Botai horses came from, which would still be compatible with the findings of the study.
In 2021, William Taylor and Christina Barron-Ortiz disputed the evidence for domestication of Przewalski's horse. Their case was rejected by Alan Outram and colleagues in a paper which was not dated or peer-reviewed. Taylor reiterated his arguments that Przewalski's horse had never been domesticated in an article in Scientific American in 2024.
In any case, the Botai horses were found to have negligible genetic contribution to any of the ancient or modern domestic horses studied, indicating that the domestication of the latter was independent, involving a different wild population, from any possible domestication of Przewalski's horse by the Botai culture.
Characteristics
Przewalski's horse is stockily built in comparison to domesticated horses, with shorter legs, and is much smaller and shorter than its domesticated relatives. Typical height is about, and length is about. It weighs around. The coat is generally dun in color with pangaré features, varying from dark brown around the mane, to pale brown on the flanks, and yellowish-white on the belly, as well as around the muzzle. The legs of Przewalski's horse are often faintly striped, also typical of primitive markings. The mane stands erect and does not extend as far forward, whilst the tail is about long, with a longer dock and shorter hair than seen in domesticated horses. The hooves of Przewalski's horse are longer in the front and have significantly thicker sole horns than feral horses, an adaptation that improves hoof performance on terrain.Genomics
The karyotype of Przewalski's horse differs from that of the domestic horse, having 33 chromosome pairs versus 32, apparently due to a fission of a large chromosome ancestral to domestic horse chromosome 5 to produce Przewalski's horse chromosomes 23 and 24, though conversely, a Robertsonian translocation that fused two chromosomes ancestral to those seen in Przewalski's horse to produce the single large domestic horse chromosome has also been proposed.Many smaller inversions, insertions and other rearrangements were observed between the chromosomes of domestic and Przewalski's horses, while there was much lower heterozygosity in Przewalski's horses, with extensive segments devoid of genetic diversity, a consequence of the recent severe bottleneck of the captive Przewalski's horse population. In comparison, the chromosomal differences between domestic horses and zebras include numerous large-scale translocations, fusions, inversions, and centromere repositioning. Przewalski's horse has the highest diploid chromosome number among all equine species. They can interbreed with the domesticated horse and produce fertile offspring with 65 chromosomes.
The mitochondrial genome has 37 genes, which are 99.63% identical to those of the domestic horse.
Ecology and behavior
Przewalski reported the horses forming troops of between five and fifteen members, consisting of a mature stallion, his mares and foals. Modern reintroduced populations similarly form family groups of one adult stallion, one to three mares, and their common offspring that stay in the family group until they are no longer dependent, usually at two or three years old. Young females join other harems, while bachelor stallions as well as old stallions who have lost their harems join bachelor groups. Family groups can join to form a herd that moves together.The patterns of their daily lives exhibit horse behavior similar to that of feral horse herds. Stallions herd, drive, and defend all members of their family, while the mares often display leadership in the family. Stallions and mares stay with their preferred partners for years. While behavioral synchronization is high among mares, stallions other than the main harem stallion are generally less stable in this respect.
Home range in the wild is little studied, but estimated as in the Hustai National Park and in the Great Gobi B Strictly Protected Area. The ranges of harems are separated, but slightly overlapping. They have few modern predators, but one of the few is the Himalayan wolf.
Horses maintain visual contact with their family and herd at all times, and have a host of ways to communicate with one another, including vocalizations, scent marking, and a wide range of visual and tactile signals. Each kick, groom, tilt of the ear, or other contact with another horse is a means of communicating. This constant communication leads to complex social behaviors among Przewalski's horses.
The historical population was said to have lived in the "wildest parts of the desert" with a preference for "especially saline districts". They were observed mostly during spring and summer at natural wells, migrating to them by crossing valleys rather than by way of higher mountains.
Diet
Przewalski horse's diet consists of vegetation. In the Chernobyl exclusion zone, Przewalski's horses consume primarily grasses and forbs, including Elymus repens, Carex spp., Fabaceae, and Asteraceae.Looking at the species' diet overall, Przewalski's horses most often eat E. repens, Trifolium pratense, Vicia cracca, Poa trivialis, Dactylis glomerata, and Bromus inermis. While the horses eat a variety of different plant species, they tend to favor different species at different times of year. In the springtime, they favor Elymus repens, Corynephorus canescens, Festuca valesiaca, and Chenopodium album. In early summer, they favor Dactylis glomerata and Trifolium, and in late summer, they gravitate towards E. repens and Vicia cracca.
In winter the horses eat Salix spp., Pyrus communis, Malus sylvatica, Pinus sylvestris, Rosa spp., and Alnus spp. Additionally, Przewalski's horses may dig for Festuca spp., Bromus inermis, and E. repens that grow beneath the ice and snow. Their winter diet is very similar to the winter diet of domestic horses, but differs from that revealed by isotope analysis of the historical population, which switched in winter to browsing shrubs, though the difference may be due to the extreme habitat pressure the historical population was under. In the wintertime, they eat their food more slowly than they do during other times of the year. Przewalski's horses seasonally display a set of changes collectively characteristic of physiologic adaptation to starvation, with their basal metabolic rate in winter being half what it is during springtime. This is not a direct consequence of decreased nutrient intake, but rather a programmed response to predictable seasonal dietary fluctuation.