Taxon Surrogate Profiles Europe # 2: Equus

            In my last article, I discussed the implications for rewilding the Asiatic wild ass (Asinus hemionus) in parts of Europe as an ecological surrogate for the extinct European subspecies which had previously occupied the continent. In this article I will be discussing the potential for rewilding with the other native European equid, the horse (Equus caballus). Wild horses went extinct in Europe much later than the wild ass did, but the process of their extinction was much more complicated. Unlike the Eurasian wild ass (a separate species from the African wild ass or domestic donkey, Asinus asinus ssp.), the horse had both wild and domestic varieties in Europe. The true European wild horse, Equus caballus ferus, was the subspecies adapted to temperate climates that recolonized the continent from the Mediterranean and the Middle-East after the last glacial, when the steppe-adapted subspecies retreated eastwards. The steppe type still exists in the form of the Asiatic wild horse, Equus caballus przewalski, which is the last remaining wild horse subspecies today. The exact date of extinction for the European wild horse is difficult to determine because it is unclear which historical records refer to truly wild horses, which to feral horses (released domestics), and which to hybrids. The phenotypic differences between wild and domestic horses would be far less obvious than between, for example, wild and domestic cattle (Bos taurus ssp.), likely because horses were bred more as riding/working animals than as meat/dairy animals. Because of this optical similarity, it is unknown whether the last reported wild horse, which was held captive until its death in 1909, was the genuine article, a hybrid, or just a regular domestic horse.

            What we do know about the true European wild horses of the early-mid Holocene is limited. We know that they were widespread over the continent, inhabiting most habitat types available, and probably represented multiple ecotypes. We also know from genetic studies that they had an unusually high variation in colouration, with four or five colour phenotypes being expressed. These include the bay, bay-dun, black, and black-dun coat colours seen in modern horses. The genetic studies also revealed the presence of the leopard-spotting or Appaloosa gene in some individuals. Different colours may have been advantageous in different habitats. Otherwise wild horses would have resembled primitive and wild horses that exist today. They would have stood about twelve-fourteen hands tall and been about the size of a working pony. They would have had primitive markings on their legs, back, and muzzles which would have been more obvious in some coat colours than others. Whether they had a standing or falling mane is subject to debate. It was originally thought that the falling mane seen in domestic horses was something that had arisen through their selective breeding process, but this was called into question when a carcass of the Beringian wild horse, Equus caballus lambei/lenensis, was unearthed from frozen soil in the Siberian tundra. This was a wild horse, appearing much like a small member of the Asiatic variety, with a dun coat and primitive markings, but it had a falling mane. It has since been speculated that this might be a trait that is useful in wetter environments, where a longer mane might better redirect water from the animal’s body. Consequently it is now thought that wild horses from these wetter environments would have had short but falling manes. All of these traits are still found in modern horses, leading to the next point of how to go about replicating the role of the European wild horse in modern European ecosystems.

            While there is only one living truly wild horse, the Asiatic subspecies, and some would prefer that it be used in its pure form as a substitute for the European subspecies in the entirety of its former range, it is worth noting that, as its descendant, the domestic horse is more closely related to the European wild horse. Domestic horse populations also have a much greater diversity of ecotypes, are much easier to obtain, and they show, albeit inconsistently, all of the colour phenotypes known to have existed in their parent species. There are of course disadvantages as well, since they are domestic animals and may show various detrimental behavioural and aesthetic traits that reflect this. Their status as domestic animals also means that there are laws dictating that they be treated like livestock, even when living in semi-feral conditions, so that they are required to have regular veterinary checks or be given supplementary feeding, which isn’t what is desired when trying to form a truly wild population. Of course this is more a limitation of policy than of the taxon. Personally I think the best thing to do is to use primitive domestic landraces from Europe as the basis for new wild herds. By mixing breeds from similar regions/habitats, we can create new, robust varieties suitable for forming wild populations.

            There would remain the issue of at least partial domesticity however. Certain traits will need to be considered when selecting breeding stock for these new herds. White markings are a trait associated with the domestication process, and should be avoided, as will colours that are not considered to be wild-type, such as chestnut, sorrel, grey, or anything else that is not bay, bay-dun, black, black-dun, or a leopard-spotted variant of one of those colours. The acceptable colour phenotypes would be as follows:

-       EE for the extension phenotype, i.e bay basecoat and not chestnut. Chestnut, e, is recessive so it may be difficult to avoid introducing into the population without proper precautions.

-       AA, Aa, or aa for the agouti modifier, A is dominant for unmodified bay, a is recessive for black. Avoid introduction of the A² allele which shows intermediate dominance for seal brown 

-       DD, Dd, or dd for the dun modifier, D is dominant for dun, d is recessive e for non-dun

-       LL, Ll, or ll for the leopard-spotting modifier, Lis dominant for leopard-spotting, l is recessive for non-spotting. Heterozygous horses may show less spotting than homozygous ones, which may be all white with spots. There are pattern modifiers but these are poorly understood.

If I understand the genetics correctly, combinations of these four loci should produce the following twenty-seven possible genotypes, and a  corresponding twelve possible phenotypes (bolded). It is worth noting that these genotypes will not be equally represented, with the leopard-spotting types being much rarer.

1.  EEAADDLL- Heavily-spotted Bay-dun

2.  EEAADDLl-  Lightly-Spotted Bay-dun

3.  EEAADDll- Non-Spotted Bay-dun

4.    EEAADdLL- Heavily-spotted Bay-dun

5.    EEAADdLl-  Lightly-Spotted Bay-dun

6.    EEAADdll- Non-Spotted Bay-dun

7.  EEAAddLL- Heavily-spotted Bay

8.  EEAAddLl-  Lightly-Spotted Bay

9.  EEAAddll- Non-Spotted Bay

10.  EEAaDDLL- Heavily-spotted Bay-dun

11.  EEAaDDLl-  Lightly-Spotted Bay-dun

12.  EEAaDDll- Non-Spotted Bay-dun

13.  EEAaDdLL- Heavily-spotted Bay-dun

14.  EEAaDdLl-  Lightly-Spotted Bay-dun

15.  EEAaDdll- Non-Spotted Bay-dun

16.  EEAaddLL- Heavily-spotted Bay

17.  EEAaddLl-  Lightly-Spotted Bay

18.  EEAaddll- Non-Spotted Bay

19.EEaaDDLL- Heavily-spotted Black-dun

20.EEaaDDLl-  Lightly-Spotted Black-dun

21.EEaaDDll- Non-Spotted Black-dun

22.  EEaaDdLL- Heavily-spotted Black-dun

23.  EEaaDdLl-  Lightly-Spotted Black-dun

24.  EEaaDdll- Non-Spotted Black-dun

25.EEaaddLL- Heavily-spotted Black

26.EEaaddLl-  Lightly-Spotted Black

27.EEaaddll- Non-Spotted Black

There are other coat colours modifiers that have arisen though the process of domestication, which should not be present in the new populations. The wildtype is recessive for all of these, making it easy to select for, except one, the cream dilution. Efforts should consequently be made to avoid using individuals which may carry the recessive form of this gene.

Domestic behaviour may also be a problem. Natural conditions may eventually breed these out, but even horses that have been feral for centuries retain the ability to be tamed, which is much more difficult for truly wild equids. These neotenous behaviours may also be detrimental towards forming proper group dynamics and avoiding predators. Potentially the easiest way to reintroduce wildtype behavioural genes to these horses is actually through limited introgression from the Asiatic subspecies. Despite having a slightly different chromosomal number, the two varieties are completely interfertile, and several hybrids already exist in Europe. The second generation hybrids will have thecaballus-type chromosomal count, and as long as only males are used to introduce new genetic material, and care is taken to avoid integration of the Asiatic X/Y-chromosome or mitochondrial DNA, it could be a positive strategy for improving the “wildness” of the new populations. The only undesirable trait they would bring in is the standing mane, which can be bred out either artificially or, if truly disadvantageous, through natural selection. The breeding process might look something like this:

Male przewalski x Female caballus

- F1 hybrid male, 1/2 przewalski, 1/2 caballus

- 65 chromosomes, przewalski Y-Chromosome, caballus X-Chromosome and mDNA

Male F1 x Female caballus

-  F2 hybrid female, 1/4 przewalski, 3/4 caballus

- 64 chromosomes, caballus X-Chromosomes and mDNA

Male caballusx Female F2

- F3 hybrid males and females, 1/8 przewalski, 7/8 caballus

- 64 chromosomes, caballus Y/X-chromosomes and mDNA

Intermingle these animals with feral herds to introduce new genetic material

As I mentioned earlier, certain native European landraces will be useful in different places, usually in the areas where they are native. I have devised a rudimentary layout of how nine different landraces might be formed for different European ecoregions. Each would theoretically be formed from four gene pools. The first gene pool for each would contribute the greatest amount of genetic material to the final type, and will be sourced from the local breed that is thought to be closest to the desired result. The second and third pools will each be formed from two additional breeds that also have desirable traits, and which will contribute genetic diversity. The fourth gene pool for all new types will be the Asiatic subspecies, which will contribute further diversity as well as wildtype behavioural and morphological traits. Each proposed type has been given a taxonomic name, with each being classified as a variety of the hypothetical hybrid subspecies Equus caballus licens, with the tentative subspecies name meaning “free”. I have also constructed a map illustrating where each of these types would theoretically be found. Keep in mind that my knowledge on these breeds is limited, and some may be more or less appropriate than the limited available information online would lead me to believe. It is also worth noting that there will be hybridization between varieties in the areas where there ranges meet, and this is to be encouraged. Purposeful translocations between areas may also be encouraged, especially where habitat connectivity is limited. The Asiatic subspecies may actually be more appropriately used in its pure form in the eastern steppic regions, but I created a hypothetical ecotype for that region as well, just so that all things would be equally considered.

The hypothetical ecotypes are as follows:

Turko-Caucasian Horse, Equus caballus licens var. caucasicus  (Yellow)

- Megrel + Kabarda/Anadolu + Karabakh/Karachay + Takhi

- Anatolian and Caucasian regions, i.e. Armenia, Azerbaijan, Georgia, most of Turkey, and the Russian Caucasus

Atlanto-Britannian Horse, Equus caballus licens var. brittanicus (Light Blue)

- Exmoor + Dartmoor/Welsh + Kerry/New Forest + Takhi

- Atlantic regions of northwestern Europe, i.e. Belgium, southern England, central/northern France, western Germany, southern Ireland, Luxembourg, western Netherlands, and Wales

Hispano-Mediterranean Horse, Equus caballus licens var. mediterranicus (Orange)

- Retuerta + Esperia/Pentro + Myzegea/Pindos + Takhi

- Mediterranean regions of southern Europe, i.e Albania, western Croatia, Greece, Herzegovina, central/southern Italy, Montenegro, southern Portugal, central/southern Spain, and western/southwestern Turkey.

Balto-Germanian Horse, Equus caballus licens var. germanicus (Light Green)

- Konik + Estonian/Lithuanian + Gotland/Vyatka + Takhi

- Continental/nemoral area of central and eastern Europe, i.e Belarus, Czechia, southern Estonia, central/eastern Germany, Latvia, Lithuania, Poland, Slovakia, southern Sweden, northern/western Ukraine, and central European Russia

Finno-Russian Horse, Equus caballus licens var. russicus  (Dark Green)

- Yakut + Altai/Priob + Icelandic/Faeroe + Takhi

- Boreal and arctic regions of the Scandinavian peninsula and northwestern Russia, i.e. northern Estonia, Finland, central/northern Sweden, and northwestern Russia

Nordo-Caledonian Horse, Equus caballus licens var. caledonicus (Dark Blue)

- Fjord + Eriskay/Nordland + Highland/Shetland + Takhi

- Northern Atlantic regions, i,e. Denmark, northern England, northern Germany, northern Ireland, eastern Netherlands, Norway, and Scotland

Austro-Carpathian Horse, Equus caballus licens var. carpathicus  (Pink)

- Hucul + Serbian/Bosnian + Karachan/Danube + Takhi

- Mountainous regions of south-central Europe, and the regions surrounding the Pannonian basin, i.e. Austria, Bosnia, Bulgaria,  eastern Croatia, southeastern France, Hungary, northern Italy, Kosovo, Macedonia, central/western Romania, Serbia, Slovenia, and Switzerland

Ponto-Caspian Horse, Equus caballus licens var. caspicus (Red)

- Bashkir + Kalmyk/Kyrgyz + Mongolian/Kazakh + Takhi

- Steppic region of eastern Europe, i.e. Moldova, eastern Romania, southern/eastern Ukraine, and southwestern Russia

Pyreno-Lusitanian Horse, Equus caballus licens var. lusitanicus (Purple)

- Pottoka + Garrano/Asturcon + Monichino/Losino + Takhi

- Coastal and mountainous regions of southwestern Europe i.e. southwestern France, central/northern Portugal, and northern Spain 

            As with the Asiatic wild ass, wild populations of horse in Europe could potentially have many ecological and cultural benefits. Ecotourism and sustainable hunting industries can be formed around these new herds, creating income from areas that have become impractical for farming practices. Their unique grazing habits and method of digestion help to create more varied vegetation patterns, allowing for greater biodiversity in smaller areas, and to open up habitat for more selective herbivores. Horses will contribute to nutrient cycling and seed dispersal more effectively than ruminant herbivores, because more plant matter survives their digestive system. They will also act as an additional prey item for returning and growing populations of wolves and bears. It is worth noting that much like the wild ass, the major predators of wild horses were not wolves, but humans, and before that large cats and hyenas, which represent more difficult reintroductions. Consequently wolves may not be sufficient for controlling these new populations. At first population management can be performed through translocation, but after that other methods will have to be explored. Hunting is one possible avenue which could potentially produce revenue, along with meat and leather. Overall the reintroduction of wild horses to Europe could be a very positive move, but there are numerous ways that it could be done, with many clashes of opinion that will need to be resolved

Taxon Surrogate Profiles Europe # 1: Asinus

            From the middle Pleistocene to the early Holocene, there were two species of the Equid family present on the European continent. These were the European wild horse (Equus caballus ferus) and the European wild ass (Asinus hemionus hydruntinus). The former of these was of the same species as the living domestic horse (Equus caballus caballus) and the Asiatic wild horse (Equus caballus przewalski), while the latter was of the same species as the living Asiatic wild ass (Asinushemionus hemionus, hemippus†, khur, kiang, kulan, and onager). Both species would have been found over large portions of the continent, maintaining their separate niches through slight but significant differences in diet and habitat preference, much as living horses and asses do today in those few areas where they remain. In this first article, the European wild ass will be discussed.

            The European ass, rather unfortunately, did not make it past the Iron Ages, after holding on to small refugia in areas of southern and eastern Europe, and in Asia Minor. Their persistence into this time is known from the subfossil record, but their relationship with humans is not well understood. It is likely that humans were responsible for their eventual extinction through a combination of hunting and habitat usage. For a time, the mysterious creature known as the “zebro” or “cebro” in Iberian legend was thought perhaps to have referred to a late-surviving population of the European ass, but the only reported skeleton turned out to be a donkey (Asinus asinus asinus), and other versions of the story claim it was actually a population of feral horses, commonly associated with the Sorraia breed.

For the past century or so, paleontologists have been undecided as to what sort of equid “Equus hydruntinus” was. Varying opinions placed it as a horse, an ass, a zebra, or even as a member of a completely distinct equid lineage only distantly related to the living varieties. Such conclusions are often unavoidable when dealing with the high scarcity and variability of bones, and the equally lofty egos of taxonomists. Genetic evidence has since placed the European wild ass quite neatly within the living hemione group, meaning that it is now most accurately described as a subspecies of the Asian wild ass, which might now more appropriately be called the Eurasian wild ass.

With its identity now firmly deduced, the question arises of how it can be replaced. The fact that, on a species level, it is not actually extinct, makes the answer to said question slightly easier. It is certainly not a new concept in ecological restoration that living subspecies can be used to fill the niche once occupied by their extinct conspecifics. If the habitat exists within Europe to support a population of Asinus hemionus, and if it is decided that this would be a positive move for much-needed biodiversity improvement, then it becomes a matter simply of importing individuals of an appropriate subspecies for a planned release.

What is the appropriate subspecies then? It just so happens that there are five to choose from. Among these is the Mongolian dzigettai (A. h. hemionus), the Indian khur (A. h. khur), the Turkmenian kulan (A. h. kulan), and the Persian onager (A. h. onager). Also included is the Tibetan kiang (A. h. kiang), which is considered by some to be a species in its own right, though this is not supported by genetic evidence. Not included of course is the European hydruntine (A. h. hydruntinus), nor the Syrian hemippe (A. h. hemippus), which went extinct in the nineteen-twenties.

The most appropriate subspecies would be one that was not necessarily the closest genetically to the European wild ass, but the one that resembled it most in habitat preference. While most would associate wild asses with deserts, scrublands, and steppes, these do not represent the whole spectrum of their original distribution. These more open and less human-friendly ecosystems were simply where the species remained after it had been driven from the wetter and more diverse areas of its range, which previously included forest-steppes, deltas, and coastal dunes. Such was also the case for the hydruntine which, during the Pleistocene, ranged over much of the European continent during both glacial and interglacial periods, but which by the early Holocene was confined to the Mediterranean shrublands of southern Iberia and Italy as well as the Anatolian and Pannonian steppes. 

            It is important to understand that subspecific designations are not always indicative of biological distinction. In some cases, such as that of the Eurasian wild ass, they are more accurately thought of as convenient names for geographically isolated populations. These populations were not nearly so closed off in prehistory, and there would have been frequent hybridization in the areas of overlap. Even today all of the hemione subspecies are completely cross-fertile. At least one hybrid population exists in the Negev desert of Israel, formed from a mixed founding herd consisting of five kulans and six onagers. This population serves as an ecological proxy for the hemippe, which would have occupied the area before its eventual extinction. The population has been successful, now numbering several hundred individuals, and has even started to expand its range north to the Negev highlands. Despite descending from such a low number of individuals, genetic diversity is maintained through social structure and from the broad genetic base inherited from their conspecific forebears. Such a strategy would possibly be advantageous for establishing new European populations as well.

            It is also worth noting that different subspecies might be better suited to different potential release sites. After all, the hydruntine showed a high degree of morphological variation across the European continent, and were it alive today it might also be classified into separate taxonomic units, as has been done in for living hemiones. I would propose, for example, that the kulan, already beginning its re-establishment on the Ukrainian steppe, might be the ideal candidate for introduction to the steppic regions of Romania, Hungary, and adjacent regions. For the steppe and brush regions of Turkey and the Mediterranean however, the onager might be better suited, due to its smaller size and familiarity with warmer climates. These same traits were found in the hemippe, and it would be that subspecies that I would be recommending were it still with us. I would also use onagers for the coastal dune habitats of the western coast, though those would likely not be amongst the initial release sites. As with the Negev population, hybridization would be an option, if genetic diversity and/or adaptability was found to be an issue. If this were the case I would recommend introgression from the khur for the onager group, and from the dzigettai for the kulan group. Seeing as kulans and onagers are the only hemiones currently found in European zoos and these are likely the populations that new wild herds would be established from, it would first be advisable to import additional kulans and onagers to increase diversity before considering hybridization.

            So ideally, we would be introducing two starting populations, from which we would later source new herds. One would be somewhere on the Pannonian steppe, while the other would be somewhere in the Mediterranean, perhaps one of the less populous areas of the Iberian peninsula. A third population could potentially be formed in Turkey, but perhaps it should wait until their political and environmental status improves. These populations would be allowed to breed until reaching the capacity of their prospective reserves, at which point they would then be used to start new populations, or to expand into new habitats on their own power. Population control would mostly be done through translocation at first, but once all available sites are at capacity, other options would have to be explored. Predation is one avenue worth considering, though predator diversity densities have significantly decreased since the onager was last present on the continent. Wolves would likely prey on European asses, as they do elsewhere, but due to the size of the animal and their various anti-predator behaviours, the number of individuals taken may not be comparable to the number of animals born. In the past, the predominant predators of wild asses were large cats, including leopards, cheetahs, tigers, and especially lions. The presence of lions (Panthera leo leo) in southern and eastern Europe is well supported for the early-mid Holocene, but their reintroduction to these areas, alongside leopards (Panthera pardus) would likely be far more controversial unfortunately. Dholes (Cuon alpinus) and hyenas (Crocuta and Hyaena) would also have been predators of the ass, but they are also now absent from these regions. Bears (Ursus arctos) and jackals (Canis aureus) might occasionally hunt foals or infirm adults, but this would be very occasional and would likely not affect the overall population. If wolf predation is inadequate, then culling for meat/leather or for sport might eventually be necessary.

            That being said, a wild ass introduction could have many potential benefits for European rewilding areas. As a poorly-known and charismatic large mammal, it has the potential to support tourism and sustainable hunting industries. It will also be quite a useful species for reinvigorating arid and semi-arid environments in Europe, especially regions where, for whatever reason, horses cannot be used. Hemiones tend also to incorporate more browse in their diets than horses, meaning they will likely affect local biodiversity in a different way. Alongside other large mammals, such as bison and red deer, they will create sand-baths and wallows, creating microenvironments for reptiles and invertebrates. Their grazing will help prevent succession and promote more varied and diverse ecosystems. Their ability to eat poor-quality forage and clip down larger swards of grass allows them to create more usable habitat for other herbivores. Overall, I think there is a lot of potential for the introduction of Asinus hemionus to Europe. Already one of the most widely distributed herbivores in the world, though certainly not the least threatened, the Eurasian wild ass could eventually be found across the holarctic, from Spain to Siberia.