There are no such things as "wild" horses anymore. Research published in Science overturns a long-held assumption that Przewalski's horses, native to the Eurasian steppes, are the last wild horse species on Earth. Instead, phylogenetic analysis shows Przewalski's horses are feral, descended from the earliest-known instance of horse domestication by the Botai people of northern Kazakhstan some 5,500 years ago.

Thought to be the world's last-remaining 'wild' horse, Przewalski's horses actually descend from horses domesticated by the Botai people about 5,500 years ago [Credit: Lee Boyd]

Further, the new paper finds that modern domesticated horses didn't descend from the Botai horses, an assumption previously held by many scientists.

"This was a big surprise," said co-author Sandra Olsen, curator-in-charge of the archaeology division of the Biodiversity Institute and Natural History Museum at the University of Kansas, who led archaeological work at known Botai villages. "I was confident soon after we started excavating Botai sites in 1993 that we had found the earliest domesticated horses. We went about trying to prove it, but based on DNA results Botai horses didn't give rise to today's modern domesticated horses -- they gave rise to the Przewalski's horse."

The findings signify there are no longer true "wild" horses left, only feral horses that descend from horses once domesticated by humans, including Przewalski's horses and mustangs that descend from horses brought to North America by the Spanish.

"This means there are no living wild horses on Earth -- that's the sad part," said Olsen. "There are a lot of equine biologists who have been studying Przewalskis, and this will be a big shock to them. They thought they were studying the last wild horses. It's not a real loss of biodiversity -- but in our minds, it is. We thought there was one last wild species, and we're only just now aware that all wild horses went extinct."

Some of the Botai horses were found to carry genetic variants causing white and leopard coat spotting patterns [Credit: Ludovic Orlando, reworked by Sean Goddard and Alan Outram]

Many of the horse bones and teeth Olsen excavated at two Botai sites in Kazakhstan, called Botai and Krasnyi Yar, were used in the phylogenetic analysis. The international team of researchers behind the paper sequenced the genomes of 20 horses from the Botai and 22 horses from across Eurasia that spanned the last 5,500 years. They compared these ancient horse genomes with already published genomes of 18 ancient and 28 modern horses.

"Phylogenetic reconstruction confirmed that domestic horses do not form a single monophyletic group as expected if descending from Botai," the authors wrote. "Earliest herded horses were the ancestors of feral Przewalski's horses but not of modern domesticates."

Olsen said the findings give rise to a new scientific quest: locating the real origins of today's domesticated horses.

"What's interesting is that we have two different domestication events from slightly different species, or separate sub-species," she said. (The Przewalski's horse's taxonomic position is still debated.) "It's thought that modern-day domesticated horses came from Equus ferus, the extinct European wild horse. The problem is they were thought to have existed until the early 1900s. But, the remains of two individuals in St. Petersburg, Russia, are probably feral, too, or at least probably had some domesticated genes."

Olsen led excavation of Botai sites associated with the earliest-known domestication of horses [Credit: Sandra Olsen]

Olsen began excavating Botai village sites in Kazakhstan in 1993 after the fall of the Soviet Union made the region accessible to western scientists. Some of the horse remains collected by Olsen were tested as part of the new study showing their ancestry of modern-day Przewalskis.

The Botai's ancestors were nomadic hunters until they became the first-known culture to domesticate horses around 5,500 years ago, using horses for meat, milk, work and likely transportation.

"Once they domesticated horses they became sedentary, with large villages of up to 150 or more houses," said Olsen, who specializes in zooarchaeology, or the study of animal remains from ancient human occupation sites. "They lived primarily on horse meat, and they had no agriculture. We had several lines of evidence that supported domestication. The fact the Botai were sedentary must have meant they had domesticated animals, or plants, which they didn't have. More than 95 percent of the bones from the Botai sites were from horses -- they were in a sense mono-cropping one species with an incredible focus. If they were hunting horses on foot, they would have quickly depleted bands of horses in the vicinity of the villages and would have had to go farther afield to hunt -- it wouldn't have been feasible or supported that large human population."

The KU researcher also cited bone artifacts from Botai sites used to make rawhide thongs that might have been fashioned into bridles, lassos, whips, riding crops and hobbles, as further evidence of horse domestication. Moreover, the Botai village sites include horse corrals.

The Botai buried horses with their snouts pointing southeast toward the rising sun [Credit: Sandra Olsen]

"We found a corral that contained high levels of nitrogen and sodium from manure and urine," said Olsen. "It was very concentrated within that corral. The final smoking gun was finding residues of mares' milk in the pottery. It's commonplace today in Mongolia and Kazakhstan to milk horses -- when it's fermented it has considerable nutritional value and is very high in vitamins."

Interestingly, Olsen found that after slaughtering horses, the Botai buried some horse skulls and necks in pits with their snouts facing the southeast, toward where the sun rose in the morning in autumn. Mongols and Kazakhs slaughter most of their horses at that time of year because that is when they retain the most amount of nutritious fat in their bodies.

"It's interesting because throughout the Indo-European diaspora there's a strong connection between the sun god and the horse," she said. "It may be that Botai people spoke an early proto-Indo-European language, and they also connected the horse to the sun god. Later in time, and this idea is in the historical record for the Indo-European diaspora, it was believed the sun god was born in the east and rode across the sky in a chariot, pulled by white horses. According to the belief, he would then die in the west and be reborn every day."

The team behind the paper believe Przewalski's horses likely escaped from domestic Botai herds in eastern Kazakhstan or western Mongolia.

Excavation at the Botai site, Northern Kazakhstan, 2017 [Credit: Alan Outram/University of Exeter]

"They started developing a semi-wild lifestyle like our mustangs, but they still have a wild appearance," Olsen said. "This is partly why biologists assumed they were genuinely wild animals. They have an upright mane, something associated with wild equids. They also have a dun coat, like the ones you see in the Ice Age cave paintings in France and Spain made when horses were wild. Their size, however, is very similar to what you see at Botai and other sites."

By 1969, Przewalski's horses were declared extinct in the wild, and all living today originated from just 15 individuals captured around 1900. Today, there are approximately 2,000 Przewalski's horses, all descended from those captured horses, and they have been reintroduced on the Eurasian steppes. In a sense, the horses have fared better than the peoples who once domesticated them.

"The Botai people seem to have vanished from their homeland in northern Kazakhstan," said Olsen. "Perhaps they migrated eastward to Mongolia since the later Bronze Age people there shared the practice of ritually burying the horse's head and neck pointing toward the rising sun in the autumn, the time of year they were slaughtered. That's a very specific shared trait."

Source: University of Kansas [February 22, 2018]

The sudden death of over 200,000 saiga antelopes in Kazakhstan in May 2015, more than 80 percent of the affected population and more than 60 percent of the global population of this species, baffled the world.

Saiga antelope [Credit: Royal Veterinary College]

In just three weeks, entire herds of tens of thousands of healthy animals, died of haemorrhagic septicaemia across a landscape equivalent to the area of the British Isles in the Betpak-Dala region of Kazakhstan. These deaths were caused by Pasteurella multocida bacteria.

But this pathogen most probably was living harmlessly in the saigas' tonsils up to this point, so what caused this sudden dramatic mass mortality event (MME)?

New research by an interdisciplinary, international research team has shown that many separate (and independently harmless) factors contributed to this extraordinary phenomenon. In particular, climatic factors such as increased humidity and raised air temperatures in the days before the deaths apparently triggered opportunistic bacterial invasion of the blood stream, causing septicaemia (blood poisoning).

By studying previous die-offs in saiga antelope populations, the researchers were able to uncover patterns and show that the probability of sudden die-offs increases when the weather is humid and warm, as was the case in 2015.

The research also shows that these very large mass mortalities, which have been observed in saiga antelopes before (including in 2015 and twice during the 1980s), are unprecedented in other large mammal species and tend to occur during calving. This species invests a lot in reproduction, so that it can persist in such an extreme continental environment where temperatures plummet to below -40 celsius in winter or rise to above 40 celsius in summer, with food scarce and wolves prowling. In fact, it bears the largest calves of any ungulate species; this allows the calves to develop quickly and follow their mothers on their migrations, but also means that females are physiologically stressed during calving.

With this strategy, high levels of mortality are to be expected, but the species' recent history suggests that die-offs are occurring more frequently, potentially making the species more vulnerable to extinction. This includes, most recently, losses of 60 percent of the unique, endemic Mongolian saiga sub-species in 2017 from a virus infection spilling over from livestock. High levels of poaching since the 1990s have also been a major factor in depleting the species, while increasing levels of infrastructure development (from railways, roads and fences) threaten to fragment their habitat and interfere with their migrations. With all these threats, it is possible that another mass die-off from disease could reduce numbers to a level where recovery is no longer possible. This needs to be countered by an integrated approach to tackling the threats facing the species, which is ongoing under the Convention on Migratory Species' action plan for the species.

This research was conducted as part of a wide international collaboration, adopting a 'One Health' approach – looking at the wildlife, livestock, environmental and human impacts that have driven disease emergence in saiga populations. Adopting such a holistic approach has enabled the research team to understand the wider significance of die-offs in saiga populations, beyond simply the proximate causes of the 2015 epidemic.

Professor Richard Kock, Professor in Emerging Diseases lead researcher at the Royal Veterinary College, said: "The recent die-offs among saiga populations are unprecedented in large terrestrial mammals. The 2015 Mass Mortality Event provided the first opportunity for in-depth study, and a multidisciplinary approach has enabled great advances to be made. The use of data from vets, biologists, botanists, ecologists and laboratory scientists is helping improve our understanding of the risk factors leading to MMEs – which was beneficial when another MME occurred, this time in Mongolia in 2017. Improved knowledge of disease in saigas, in the context of climate change, livestock interactions and landscape changes, is vital to planning conservation measures for the species' long-term survival"

Professor EJ Milner-Gulland, Tasso Leventis Professor of Biodiversity at Oxford University, said: "This important research was possible due to a strong partnership between European universities, governmental and non-governmental Institutions in Kazakhstan, and international bodies such as the Food and Agriculture Organisation and Convention on Migratory Species, as well as generous funding from the UK government and conservation charities worldwide. During the more recent saiga disease outbreak in Mongolia, this international partnership was useful for supporting in-country colleagues, for example by providing emergency response protocols. It's excellent to see the real-world value of research partnerships of this kind, and the great advances we have made in understanding disease in saigas thanks to such a productive collaboration."

Mr Steffen Zuther, Project manager for Kazakhstan at the Frankfurt Zoological Society/Association for the Conservation of Biodiversity of Kazakhstan, said: "This research is not only the first of its kind through its complexity and interdisciplinary approach, it also helps in capacity building inside Kazakhstan and shaping the public opinion towards a more evidence based thinking. MMEs are a major threat for the saiga antelope and can wipe out many years of conservation work and saiga population growth in just a few days. Therefore, understanding these MMEs, what triggers them and what can be done to combat them is extremely important to develop effective saiga conservation strategies. The triggering of such MMEs in saiga through weather conditions shows that not much can be done to prevent them occurring, and therefore how important it is to maintain saiga populations of sufficient size for the species to survive such catastrophes."

Professor Mukhit Orynbayev, Senior Researcher at the Research Institute for Biological Safety Problems, Kazakhstan, said:"Kazakhstan plays a crucial role for the conservation of saiga, and its government takes this very seriously. This research is an important component of the government's strategy for the conservation of the species, and we as researchers are grateful for the support we have received during our work. Through several years of work on this subject, the team of the RIBPS has gained experience in fieldwork and laboratory tests. This allows us to react quickly to any disease outbreak and get a diagnosis for it."

The research paper was published in Science Advances.

Source: Royal Veterinary College [January 18, 2018]