A sneak peek into my book

Today I want to give you a little sneak peek into my book so that you can see what you can expect from my book "Breeding-back wild beasts: aurochs, wild horse and quagga". Now available on Amazon. 

Life reconstructions, anatomical drawings of all types of aurochs 

 

Lots and lots of photos of "breeding-back" cattle, including brand new previously unreleased photos of the Hortobagyi animals

Previously unpublished reconstructions of wild horses

Reconstructions showing the variation within the quagga

The cover; I'll reveal the bull on the cover in an upcoming post

Why Equus ferus should not be used for the wild horse

The use of the binominal name Equus ferus for the wild horse is extremely common, and I used it myself in the past. However, this binomen is problematic and should not be used except in a list of synonyms of Equus caballus. 

My readers will know that I prefer to use Bos primigenius for the aurochs, thus the later-published binomen that is frequently used for the wildtype, while I treat the species of the horse (including the wild horse and its domesticated derivatives) under the name Equus caballus, which is usually used to refer to the domestic form only. This may seem inconsistent at first, but examining the problem at a deeper taxonomical level shows that it actually is not. 

I prefer Bos primigenius because this binomen has a holotype that is undoubtedly a wild specimen, the Haßleben aurochs skeleton, while Bos taurus lacks a holotype or lectotype. Type specimen are important because they clarify which species is referred to by the name. Which species is Bos primigenius? The species that the Haßleben skeleton belonged to, whatever a species definition you work with, no matter how narrow or wide your species definition is. Thus, the lack of a type specimen is problematic because it makes the situation far more ambiguous. 

As for the horse, neither Equus caballus nor Equus ferus have a type specimen. For Equus caballus, this is less problematic because it referred to domestic horses, while for Equus ferus it is a big problem because of synonymity. If two binominal names are synonymous, i.e. they refer to the same species, the rule of priority of the ICZN dictates that the name that was published first is the one to be used (the senior synonym), while the younger one is the junior synonym (as a side note, synonymity does not make the junior synonym invalid [as long as it is described accordingly to the rules of the ICZN], as it is often believed, it just means that it does not have priority and shall not be used). In the case of domestic animals, where the binomen that was erected for the wildtype exclusively often is the junior synonym, opinion 2027 of the ICZN allowed the use of the names for the wildtypes for the entire species. This includes Bos primigenius, but also Equus ferus. The ICZN explicitly assumed in opinion 2027 that Equus ferus is based on the ancestor of domestic horses, which they call “tarpan” in their document. For Bos primigenius, there is no problem following opinion 2027 because it is based on a specimen that was indeed a member of the wildtype of cattle, for Equus ferus there is indeed a problem. In order to see if Equus ferus is justifiable as the binomen of the wild progenitor of the domestic horse, we have to look at the original description of this name. 

I used Equus ferus in the past because, like everyone else, I did not check the original source and assumed that everything is alright with that name. This is the reason why it is that widely used as the name for the wild horse. For some reason, I assumed Equus ferus was based on fossil or subfossil remains of definite wild horses in Europe. When I checked the original source, I realized that this name should not be used for the wild horse. 

Equus ferus is introduced by Pieter Boddaert in his 1785 work Elenchus animalum. Boddaert gives a short description mentioning long ears, a short curly mane, a blackish grey mouse-coloured body and a short tail, and refers to the written description of alleged wild horses encountered by S. G. Gmelin in Voronezh in 1769. That is the original description of Equus ferus. The big problem is that it is far from clear what those horses spotted by Gmelin were. Whether the horses were wild, feral or hybrids of wild and feral horses. The description fits what other writers reported of free-roaming horses at that time and region. At least one member of the herd was a black domestic mare, as reported by Gmelin himself. It is generally unclear what the horses of that time and region were, and there never was a consensus among authors, be it contemporaneous ones or after the extinction of those populations in the 19^thcentury to this day. And in the lack of a type specimen, be it a holotype or a lectotype, it cannot be ascertained anymore. This case shows why type specimen are important. 

Therefore, there is no certainty that Equus ferus is based on a wild representative of the species that includes the domestic horse. If domestic animals and their wildtypes are regarded as separate species, the name to be used for the species of the wild horse would be Equus przewalskii because this binomen was the first one to be erected based on an undoubtedly wild specimen of the species. It has both a holotype and paratype which were wild Przewalski’s horses. I usually treat wild and domestic animals as members of the same species, and the first name erected for this species is undoubtedly Equus caballus by Linnaeus 1758. Linnaeus also erected a senior synonym for Bos primigenius, namely Bos taurus. However, in this case I prefer to follow opinion 2027 because the junior synonym conserved is based on a type specimen that was undoubtedly wild, while Equus ferus is based on a description which itself is based on a description of an encounter with horses of unknown status. Therefore, following opinion 2027 in the case of Equus ferus is not useful. For the same reason Equus ferus should not be used on subspecies level for the subspecies that was ancestral to the domestic horse. There is not the slightest bit of scientific evidence that the horses encountered by Gmelin in 1769 were members of the form that was domesticated 5000 years ago. For the same reason Equus ferus should not be used for Pleistocene wild horses. It should not be used for wild horses at all. If one wants to use Equus ferus solely to refer to the horses historically called “tarpan”, it is questionable if these populations deserve a subspecies status as it is unclear what those horses were. So neither Equus ferus nor Equus ferus ferus are taxonomically justified. 

This of course leaves the question what the subspecies that was the predecessor of the domestic horse should be called then. For this question to be answered, a rigorous assessment of the Holocene wild horse material that has been found in Eastern Europe would be necessary. It is well possible that someone already erected a taxon based on that material that would have priority. Whether or not a Pleistocene wild horse name (and there are a lot of those) is applicable to this form remains to be seen, this would have to be morphologically and genetically evaluated. When a subspecies is not yet scientifically described, it is referred to as species X ssp., in the case of the wild horse that was ancestral to the domestic horse it would be Equus caballus ssp. – a possible way to “rescue” Equus ferus is to assign undoubted Holocene European wild horse material to Equus ferus as a lectotype. As long as this has not been done formally, Equus ferus should not be used as the binominal name of the wild horse. 

 

Extinct megafauna that could be revived using genome editing

Humans wiped out countless species of animals. Some of those species, particularly those that died out comparably recently, might actually be retrievable. Usually, cloning comes to mind when talking about reviving extinct animals. However, somatic nucleus transfer for reproductive cloning requires an intact cell and not just the DNA of the animal, which is why it is not available for most species wiped out by man. However, there are a few megafaunal species that have been wiped off from which we have at least one and in some cases several complete genomes. If there is a still extant species that is closely related and would make a suitable surrogate, it would be possible to exchange the alleles specific for species A with those for species B and thus creating a viable cell with the genome of the extinct species in question with genome editing. This limits the number of extinct animals that could be revived. For example, I would imagine it to be pretty difficult if not impossible for a species like the thylacine, which has been evolutionary separated for 30 million years from its closest living relatives. In some cases, it could be easy and much less effortful because of the lower number of genes that differ and the suitability of the surrogate because the animal has a very close living relative. In this post, I present a number of megafaunal species from which full genomes either have been acquired or at least could potentially be acquired and which have a more or less closely related relative that can be used for genome editing and as a surrogate. The mitochondrial DNA of the resulting animal would be that of the donor cell, which would be from the related species. However, as mitochondrial genes are highly conserved among mammals this would not have much of an influence. Using closely related species also has the advantage that the behaviour will be rather similar, especially among the large herbivore species that I am going to list. This makes the rearing by a surrogate mother and socialization of the result less problematic or maybe not even an issue at all. 

I see reviving an extinct animal that has been wiped out by man as a contribution to species conservation just as breeding an endangered species or subspecies. One might ask, particularly in the case of wiped-out subspecies, why doing that at all if there are suitable ecological proxies. Occasionally some even question the need to conserve endangered subspecies such as the Northern White rhino because their conspecifics from other subspecies would function ecologically the same or very similar. Personally, I cannot relate to that mindset. Conservation is about preserving biodiversity and the preservation of evolutionary more or less distinct subspecies is a vital part of that. The same goes for reviving extinct species or subspecies – it would greatly increase the biodiversity again, after it has been depleted by man when the species or subspecies was wiped out. 

 

Bubal hartebeest, Alcelaphus buselaphus  

This animal is sometimes also considered a subspecies, but that question is merely taxonomical and not relevant for “de-extincting” the animal. In any case, other members of Alcelaphus could be used for genome editing and as a surrogate. Many individuals must have been preserved as trophies, and it is potentially possible to acquire full nuclear genomes from them. 

 

Bluebuck, Hippotragus leucophaeus  

Other members of Hippotragus could be used as a surrogate and for genome editing. It can be tried to acquire a fully nuclear genome from taxidermies.  

 

European aurochs, Bos primigenius primigenius

One full nuclear genome has been resolved in 2015 from a well-preserved Neolithic bone. Considering the richness of recent aurochs material, it could be possible to obtain quite a few more complete genomes. And there is a very close living relative, modern cattle. The number of genes that would have to be exchanged would probably be lower than in most of the other cases I am listing here, and also the surrogate and the procedure of implanting an embryo would be completely unproblematic. And considering the similarities in behaviour between cattle and aurochs, socialization will not be problematic either. For these reasons, I consider the aurochs one of the most realistic candidates for a revival through genome editing. Even if the resolved genome remains the only one to be fully resolved, one revived aurochs individual still can be outbred using aurochs-like cattle. I wrote a post on that a few years ago. 

 

Several types of wild horses 

There are well-preserved mummies of Siberian wild horses, Equus caballus lenensis, and one of the Yukon wild horse, Equus caballus lambei, so it could be possible to obtain fully resolved nuclear genomes from that. A domestic horse could be used for genome editing and as a surrogate. Even if only one genome can be obtained, the revived horses can be outbred with Przewalski’s horses and/or robust landraces in the same manner as I suggested for revived aurochs. 

 

Kouprey, Bos sauveli  

Numerous kouprey specimen have been preserved as trophies and one skin. It could be possible to obtain full nuclear genomes from that very recent material. The closest living relative is the Cambodian banteng which hybridized with the kouprey in the past. It can be used for genome editing, as a surrogate and even for outbreeding if necessary. 

 

Quagga, Equus quagga quagga  

The quagga is not and cannot be bred-back from extinction with living Plains zebras, which is why it would be desirable to try to acquire full genomes from the numerous preserved skins and the few skeletal material that is preserved of this zebra. The zebras of the Quagga Project can be used for genome editing, as a surrogate and outbreeding if necessary. 

 

Pyrenean ibex, Capra pyrenaica pyrenaica  

This is the only extinct animal that has been cloned so far, unfortunately the clone died shortly after birth. Genome editing with individuals from other subspecies of Capra pyrenaica could be more successful, they can be used as surrogates and for outbreeding. 

 

Steppe bison, Bos (Bison) priscus  

There are plentiful of remains from steppe bison, including soft tissue. Perhaps it would be possible to obtain full nuclear genomes from that. Needless to say, that still existing bison, be it European or American, can be used for genome editing, as a surrogate and outbreeding. 

 

? Woolly mammoth, Mammuthus primigenius  

Currently, there is no de-extinction project in the strict sense focusing on the woolly mammoth. There is the attempt to create a “mammophant” by introducing mammoth alleles for certain traits into the genome of an Asian elephant, what is not what I would consider de-extinction in the strict sense. If doing that is possible, it might also be possible even if more effortful, to exchange all alleles of genes where Asian elephant and woolly mammoth differ. However, since implanting an embryo into an elephant is very complicated, and those who want to create plan to use an artificial womb, a technique which does not exist hitherto, I wonder if it is feasible to recreate the woolly mammoth for practical reasons. 

 

Caucasian Wisent, Bos (Bison) bonasus caucasicus  

Several skins and trophies of this wiped-out subspecies (or species or variety, there is no consensus on its taxonomic status) exist, so it could be possible to obtain full nuclear genomes from it. European bison of the Lowland-Caucasus line, which partly descend from the last Caucasian wisent bull, could be used for genome editing, as a surrogate and for outbreeding. Obtaining genomes from remains of wisent prior to the bottleneck in the 20^th century could also help to greatly increase the very limited genetic diversity of this endangered bovine. 

 

Cave lion, Panthera spelaea  

Several very well-preserved pubs of this feline have been found. It might be possible to acquire full nuclear genomes from that, and the closely related actual lion would be suitable for genome editing and as a surrogate. 

 

Schomburgk’s deer, Rucervus schomburgki  

Some remains of this deer species exist, a sister species from the Rucervus clade could be used for genome editing and as a surrogate. 

 

Japanese sea lion, Zalophus japonicus

There are taxidermied specimens of this sea lion, related species of the Zalophus clade can be used for genome editing, as a surrogate and possibly outbreeding if necessary. 

 

Caribbean monk seal, Neomonachus tropicalis

There should be some remains of this recently extinct species, the related Hawaiian monk seal can be used for genome editing, as a surrogate and possibly outbreeding if necessary. 

 

One common objection against the revival of extinct animals is “one individual is not enough to build a population”. Apart from the fact that even one individual could tell us a lot about the extinct animal species/subspecies, it could be possible to get several genomes of those recently extinct species. Getting the full genome of five or ten individuals from different regions and times would probably enable to get a genetic diversity comparable to that of the modern wisent population, which descends from only twelve founding individuals from the same population. Some wisent individuals show inbreeding-related problems, but not to the extent that it threatens the survival of the species. An even more extreme example would be the Mauritius kestrel. Apart from that, related species/subspecies can always be used for outbreeding to add genetic diversity. Hybridization among related species with neighboring or overlapping distributions is very common in the animal kingdom. 

 

Koniks with a standing mane in Oostvaardersplassen

Some Konik ponies have a standing mane. This is likely the result of Przewalski's horse introgression, as the crossing-in of this wild equine is documented in the Konik pedigree [1]. I have seen such specimen especially often on photos from Polish breeding sites, such as Popielno, which is one of the most important Konik breeding sites in Poland. There are also very Konik-like ponies in Germany that can have an upright mane, but those are likely to be Heck horses (both breeds are used indiscriminately in grazing projects, there is no breeding book so they are virtually indistinguishable in Germany). But the ponies at Oostvaardersplassen are "pure" Koniks in any case, mostly purchased from Popielno. I have not seen any OVP ponies with a standing mane until I found a relatively recent video on youtube, go here. Sometimes a domestic horse can have a standing mane when it is not fully grown yet (all foals have a standing mane), and sometimes it looks as if the horse has a standing mane when viewed from the side when the bulk of the longer hair of the mane falls to the other side and the shorter hair at the edges of the mane are standing, but I think in this case it is rather clear that those are truly fully grown Koniks with a standing mane, see shots like 1:27. It is interesting to see that also in OVP, the largest Konik breeding site in western Europe, there are individuals with a standing mane. Particularly interesting is the question if the frequency of individuals with a standing mane would increase over time if it provides a fitness advantage, as there is no artificial selection on those ponies. 

[1] Jaworski 1997: Genealogical tables of the Polish primitive horse. Polish Academy of Sciences. 

The coat colour variation in the Przewalski's horse #2

In the previous post, I wrote that wild-caught Przewalski’s horses from the 19^th and early 20^th century displayed more colours than the modern population does after the genetic bottleneck in the middle of the 20^th century. These colours included the lack of pangare, lightly coloured legs, possibly non-dun (at least a rather dark colour instead of the light sandy colour that many individuals show), and very lightly coloured individuals. 

In the comments, two photos were linked that, however, undoubtedly show modern Przewalski’s horses lacking pangare. They are from the population at the Hustai National Park in Mongolia and can be seen here (photo #1) and here (photo #2). 

This shows that the non-pangare allele is definitely still present in the population, albeit its frequency seems to be greatly reduced. What is also interesting is how dark the colour of the non-pangare individual on photo #2 is. It is not quite as dark as the stallion Schalun from the early 20^th century which I mentioned in the previous post, but it is certainly darker than a Gotland pony, which has been found to carry both the non-dun1 and the domestic non-dun2 allele, but not the dun allele. I think it is not unlikely that this individual has the non-dun1 allele – when you compare it with the stallion on photo #1, which is definitely bay dun, you can see a clear difference to the individual on photo #2. Looking at the other individuals on photo #2, it seems that they have the same base colour on the neck and face, and the rest is diluted by pangare, which is very prominent on these individuals. So they might have the non-dun1 allele too. If that is really the case, the non-dun1 allele might be present in more modern individuals than only those in this herd, just not as apparent because the colour is diluted by pangare and non-pangare individuals are pretty rare in the modern population. But without a genetic test on the Dun locus in these individuals this is a speculation. 

This sparked my interest in the Hustai herd and I searched for images on google. As it happens, I even found an individual with lightly coloured legs (go here). I also found a rather pale individual from Hustai NP, but it was in its winter coat and the winter coat is always lighter in colour. 

 

This shows two things: some of the colour variants considered extinct by the sources I cited in the previous post are still present in the modern Przewalski’s horse population, and the Hustai herd seems to be rather variable in colour. I am curious on the background of this herd – since the Przewalski’s horse was killed off from the wild in the 20^th century, this herd must descend from individuals in captivity, and I wonder which location(s) the animals are from as they preserve all these colour variants that have become incredibly rare in the modern population. 

The original coat colour variation in the Przewalski's horse

The modern Przewalski’s horse has a comparably uniform coat colour: a bay dun base colour often with a reddish tone, combined with the prominent countershading and white muzzle (pangare). This has become the standard colour scheme for wild horses. There is some variation, some individuals are more reddish than others, some are more lightly beige in colour, but apart from that, current Przewalski’s horses do not vary greatly in colour. 

However, what we see in modern Przewalski’s horses is the result of the genetic bottleneck due to the population crash in the 20^th century. Photos and descriptions of individuals prior to the genetic bottleneck event from the late 19^th century and early 20^th century show that originally there was much more variation in the coat colour of the Przewalski’s horse than what is the case now, also including colour alleles that have disappeared from the modern population. 

There were both very dark and also very lightly coloured individuals in the herds. They were not geographically separated but from the same populations and were often sold together [1]. An example for such a lightly coloured individual was a stallion caught from the wild and brought to the Haustiergarten Halle, Germany, in 1901 [1]. Some modern Przewalski’s can be more lightly coloured than others even today, but the photos show that some individuals prior to the bottleneck were very light in colour. A famous example for a dark individual is the stallion Waska, which was the first Przewalski’s horse brought to Europe and could be ridden [1] (you find a photo of him on Wikipedia). The photos of this and other dark individuals show that the countershading is slightly reduced, and that the colour is way darker and less shaded than in the modern Przewalski’s horses. I think it is well possible that these dark individuals had the non-dun1 phenotype caused by the d1 allele being present homozygotely on the Dun locus. This allele has been found in a 42.000 years old wild horse and a roughly 4.000 years old horse, both from Siberia [2]. The youngest date for the separation of the Przewalski’s horse’s lineage and that of the domestic horse was 38.000 years ago [3], making it possible that the non-dun1 allele was present in the wild populations before the lineages separated. Another stallion from the early 20^th century that was documented in photographs, named Schalun [1], was so dark that I think it is very unlikely that it had the dun dilution. It does not look as if it was the domestic non-dun2 mutation, the colour resembles much that of some Gotland ponies, which were found to have the d1 allele [2]. It is of course possible that Przewalski’s got the d1 allele via introgression from domestic horses but considering that the allele was already present in late Pleistocene wild horses, it is more parsimonious that the dark-coloured Przewalski’s horses were a reflection of the original wildtype diversity in the wild horse, if those individuals indeed had the d1 allele. 

Pangare (light ventral countershading with a white muzzle) is typical for wild equines, and all modern Przewalski’s horses have it. However, it was not uncommon that wild-caught Przewalski’s horses completely lacked pangare, f.e. many of the wild horses brought to Askania Nova in the early 20^th century [1]. These horses lacking pangare must have had the non-pangare allele Pa^np. It is certainly possible that this was the result of domestic horse introgression in the wild that undoubtedly took place, but I think it is also plausible that this allele first appeared in wild populations, as some cave paintings show horses that definitely lack pangare. Cave paintings, however, must be taken with caution. Only a genetic test of predomestic wild horse DNA samples could clarify if non-pangare was a wildtype or a domestic allele. 

There were also individuals with lightly coloured legs. Usually, in wildtype-coloured horses (be it bay, bay dun, black, black dun) the distal half of the legs is coloured dark to very dark, except for a light area at the back of the leg of varying extent. Apparently in some individuals this light area extended across the entire leg, resulting lightly coloured legs. There is at least one photograph of an individual having such legs [1], and descriptions of wild Przewalski’s from the late 19^th century mention lightly coloured legs. 

 

I did an illustration of the original coat colour diversity found in the Przewalski’s horse. It shows, from top to bottom and left to right, the colour type that is now prevailing in the population, the dark variant that is possibly non-dun1, the non-pangare one (I combined it with the dark variant, based on the stallion Schalun, but of course also lighter coloured ones could be non-pangare), the lightly coloured legs, and the very lightly coloured variant. All these illustrations are based on photographs of actual individuals that lived in the early 20^th century and often were caught from the wild. 

 

What happened to the colour variants not present in the modern gene pool anymore? One reason for their disappearance was the population crash in the 20^th century, which caused a reduction in allelic diversity. Another reason is, in fact, selective breeding. It was very likely the case that the lighter-coloured individuals with pangare and visible leg stripes were preferred in breeding because the responsible breeders thought that a wild horse must look that way [1,4]. This idealization of the Przewalski’s horse appearance caused these colour variants to disappear – there are no non-pangare individuals anymore (EDIT: There are in fact some non-pangare individuals surviving in Mongolian herds at least), and also no very dark, possibly non-dun, but also no very lightly coloured ones [1,4]. I do not think these variants were actively selected against, but apparently nobody paid attention on preserving them in the gene pool, resulting in their disappearance. 

 

The current Przewalski’s horse is not completely free of domestic horse introgression. As a consequence, domestic colour variants occur from time to time. Some herds may have individuals with a white stripe on the face [1], others show a chestnut colour [1,4], what means that the e mutation on the Extension locus has been introduced into the Przewalski’s horse gene pool by interbreeding with domestic horses. 

 

Therefore, while some wildtype colour variants have been lost in the last remaining wild horse, domestic ones have been introduced. This is of course not desirable for maintaining the original wildtype diversity. This could, theoretically, be fixed. For example, herds in which chestnut Przewalski’s have appeared could be tested for the eallele, and those selected out, what, on the other hand, bears the danger of selecting out wildtype diversity that is needed in the limited gene pool. The non-pangare allele could be reintroduced either by gene editing (which would be effortful) or crossing in a non-pangare domestic horse (which would be controversial for good reasons). But it is questionable if single colour alleles are really that important. 

EDIT: modern representatives of these colour variants can be seen here. 

 

Literature 

 

[1] Volf, Jiri: Das Urwildpferd. 1996. Neue Brehm-Bücherei. 

[2] Imsland et al.: Regulatory mutations in TBX3disrupt asymmetric hair pigmentation that underlies Dun camouflage colour in horses. 2015.

[3] Orlando et al.: Recalibrating Equus evolution using the genome sequence of an early Middle Pleistocene horse. 2013.

[4] Oelke, Hardy: Wildpferde gestern und heute – Wild horses then and now. 2012. 

Genetic research not done yet that would be helpful

Genetics are vital for understanding the evolution and domestication of horses and cattle. In recent years, genetic studies have helped to clarify where, when and how many times cattle and horses have been domesticated, which genes were involved, in the case of the horse and even resolved aspects of the phenotype of the extinct European wild horses. Genetics are also very important for breeding and thus for “breeding-back”. But a lot more research could be done to properly understand the aurochs, wild horse and their domestication. Often on my blog I am forced to engage in wild speculations because the genetic framework of the topic I am writing about has not been done yet. With this post, I want to give some impulses for genetic research not done yet that would be very useful for the topic of “breeding-back”, the aurochs and European wild horses.

 

- Resolving more coat colour loci and alleles in cattle. Many of the colour alleles in cattle are hypothetical, because the genetics of cattle colours are not as well-resolved as in dogs or horses for example. Thus, a rigorous study resolving many of the common cattle coat colour alleles would be fine, f.e. one that resolves the allele that is responsible for the recessive lack of red pigment in Podolian cattle, Tudanca, Grauvieh and Chianina, or the allele(s) that remove the rest of the pigments in the hair of Chianina. Resolving these recessive alleles and developing tests for those alleles would greatly help to remove them from “breeding-back” populations. 

- after that, testing the colour alleles in aurochs DNA samples. Studies have been done that resolved the colour genotypes of predomestic wild horses, which also revealed some surprises (f.e. that the leopard spotted complex was found in wild horses). It would be awesome if the same would be done with DNA samples from the aurochs. It could reveal surprises too. 

- Researching how many loci were affected in the domestication of the aurochs. That’s surely not an easy task, but it would be very interesting to know on how many loci aurochs and cattle differed, and if there are differences among cattle breeds. Some cattle breeds might differ from the aurochs on fewer loci than others.  

- Finding some key genes that had a role in the domestication of the aurochs and resolving the alleles. This has been done for horses in a recent study, it found two genes that probably had a key role in the domestication of the horse. The same could be done with cattle and aurochs. This would also be helpful for recreating the aurochs or at least creating an aurochs-like animal with the CRISPR-Cas9 method. 

- Studying the genetic background of the sexual dichromatism in Bos primigenius. It would be very interesting to know which loci and which genetic mechanisms are responsible for the sexual dichromatism seen in aurochs and cattle. Identifying individual alleles that are responsible for the well-marked dichromatism seen in the aurochs would also help to select for this trait in “breeding-back” cattle. 

- Resolving some genes involved in horn size and curvature. Currently, only two loci involved in the production of bovine horns are identified, the Polled locus and the Scurred locus. They only determine if the individual is polled or not and if the horns are scurred or not. But the genes involved in horn size and curvature are not studied. Horn size is likely a quantitative trait, but maybe there are one or a couple of loci that have a particularly large impact on horn size. Curvature is probably polygenic as well. If some loci involved in those two traits are resolved, the alleles found in the British aurochs of which the genome has been resolved in 2015 could be checked and traced down in living cattle, what would making selecting for aurochs-like horns much easier than it currently is. 

- Examining the Y chromosome of the Konik pony. So far, only the mitochondrial genome of the Konik pony has been examined. As domestic horses have a very limited Y chromosome diversity, finding unique haplotypes would be a strong hint for recent wild horse introgression, which would be the case if the Konik myth would be true. This, however, is very unlikely and it would be very nice to have it confirmed that also on the Y chromosome the Konik is a usual, robust domestic horse and not a surviving wild horse or a recent wild horse descendant.

- Resolving haplotypes in predomestic European wild horses and trying to trace them down in domestic horses. This would help to clarify how much wild horse introgression into the domestic horse gene pool there was in Europe, and also which breeds might have more influence from native European wild horses than others. 

- Testing European wild horses for the dun allele. So far, the dun locus was tested only for two Siberian wild or ancient horses, which is a way too small sample size to tell us about the frequency of the respective alleles. Also, the locus was not examined in European wild horses, so that we do not know with certainty if they were black or black dun. 

 

 

Which horses should be used for a reintroduction in Europe's nature?

The discussion which horse breed or type is closest to the European wild horse and which horses should be used for a reintroduction of the species into European nature systems is sometimes carried out rather controversially and is sometimes needlessly emotionalized. In recent years, a variety of horse landraces have been used for “rewilding”, including the Konik pony, the Exmoor pony, the Garrano pony, the Hucul, Retuerta, Sorraia and the Bosnian Mountain horse. Some of them have popular background stories that claim they are, respectively, the most recent descendants of the European wild horse – none of these popular background stories are scientifically tenable. That does not make those breeds any more, or any less, suitable for natural grazing projects or even establishing truly feral populations. The Konik pony and the strongly Konik-influenced Heck horse are most frequently used in natural grazing and “rewilding” projects, probably due to their scientifically untenable reputation of being wild horses, recent wild horse descendants or phenotypic copies of the European wild horse. However, the range of pony or horse breeds used in “rewilding” is slowly diversifying. Currently, the only place in Europe where horses live completely free of human influence (except for poaching, unfortunately) is the Chernobyl exclusion zone, where a population of about 100-200 Przewalski’s horses thrives. They also happen to be true wild horses instead of domesticates. But which type of horse should be used for a reintroduction of Equus caballus into European wilderness?

One of the problems we face when trying to resolve that question is, apart from all the confusion that the mythologized breed origin stories of certain landraces have created, that we do not know how the wild horses in Europe exactly looked like. Not a single complete skeleton of a Holocene, predomestic European wild horse has been described so far. It is likely that it had the robust pony morphology with a thick head, as this morphotype is found in the closely related Przewalski’s horse and Pleistocene wild horse skeletons from Europe. But we do not know the morphology for sure. What is much more certain is the colour phenotypes, as the colour loci of ancient DNA samples from European wild horses have been tested for the respective alleles. It turns out that during the early and middle Holocene, both bay dun (the colour of the Przewalski’s horse) and black dun (the colour found in Koniks, Hucule and Sorraias) were found in European wild horses. During the later Holocene, however, black dun became the prevalent phenotype as a//a is the prevalent genotype found in the ancient samples [1]. It is also possible that non-dun wild horses existed in Europe, but the Dun locus has not yet been tested in European wild horse samples. I believe that it is likely that dun was prevalent (go here). A tricky question is the mane of Holocene European wild horses. All wild equines today have a standing mane, while hanging manes are found exclusively in domestic horses and donkeys. Nowadays I think it is much likelier that European wild horses had a standing mane as all other living wild equines do (go here for a post). 

It is also important to note that there was not one European wild horse during the Holocene, but at least two subtypes: Iberian wild horses and wild horses on the rest of Europe. It turns out that, genetically, Iberian wild horses are less closely related to the ancestors of domestic horses than the Przewalski’s horse [2]. Furthermore, it is important to note that the range of wild horses was likely continuous from Europe to Asia and that there was a continuum between European wild horses and the Asiatic Przewalski’s horse, as introgression from the latter subspecies has been found in a European wild horse stallion’s DNA sample [3]. 

 

Combining these facts, there are two concepts for horse reintroduction in Europe that I prefer. I cannot decide which one of the two concepts I favour as both have pretty strong pro-arguments. I see that there are diverse options for “rewilding” horses on this continent and that each project is free to pick those types of horses they prefer, but I think there should be a somewhat consistent baseline for why choosing a particular breed for a true reintroduction into European nature, at least in my opinion. By true reintroduction I mean the establishment of self-sustaining, unregulated horse populations in a nature system or wilderness area. 

 

1. Using pure Przewalski’s horses 

 

There are two very obvious arguments for choosing Przewalski’s horses exclusively for the reintroduction of horses into Europe’s nature. For once, they are the only wild horses left. It is true that the Przewalski’s horse is the Asiatic subspecies, and therefore not the native subspecies, but it has to be considered that it is closer to European wild horse subspecies outside Iberia than the Iberian wild horse was, and that there apparently was a continuum between both subspecies. Furthermore, it is very likely that the Przewalski’s horse would have recolonized the European continent after the man-made extinction of wild horses in Europe if it had not been for human influence. It is true that the habitat of the Przewalski’s horse was restricted to the steppe in historic times, but we do not know the natural plasticity of the ecotype as it might have also inhabited other biomes previously. Przewalski’s horses do very well in grazing projects in Central and Western Europe and also wild in the European wilderness as the Chernobyl population demonstrates. The second argument for using Przewalski’s horses exclusively is that it would be a very valuable contribution to the preservation of this endangered last remaining wild horse subspecies. The Konik population in Oostvaardersplassen numbers around 1000 individuals – image Przewalski’s horses would have been chosen for that initiative. It would have grown to the largest single Przewalski’s horse herd on the continent (or perhaps even the entire world). There are dozens of grazing projects in Germany alone, if all of them chose Przewalski’s horses instead of domestic horses it would not take long until the last wild horse on this world is not endangered anymore. 

The question then is, why are not all “rewilding” and grazing projects using the Przewalski’s horse? This has two very practical reasons. First of all, the Przewalski’s horse is not just another domestic breed, but a genuine wild animal with the behaviour of a wild animal. They can be very aggressive, particularly the stallions, and may attack humans. Przewalski’s horses are very difficult to handle. The other reason is that Przewalski’s horses are not as easily available as domestic breeds are. 

 

2. Using hybrids of Przewalski’s horses and robust landraces 

 

The second concept is using hybrids of Przewalski’s horses and robust landraces that are adapted to the climate and vegetation of the respective region. The reason for that is that European domestic horse breeds are the descendants of the European wild horse, and thus there is a chance that they preserve at least some of the wildtype alleles that were unique for this wild horse type. The Przewalski’s horse should be in the mix because it is a wild horse with a wildtype morphology, genetics and behaviour. This would also create a greater genetic diversity than using Przewalski’s horses only, as they have a limited genetic diversity due to their genetic bottleneck during the 20^thcentury. As a continuous range of free-roaming horses from Iberia to Asia is illusional in modern times, there is no danger of intermixing between pure Przewalski’s horses that have been released back into the wild and the hybrids in isolated European reserves. 

Creating hybrid populations of Przewalski’s horses and robust domestic landraces is also the chance to mimic the phenotype of the European wild horse. As mentioned above, the exterieur of that wild horse type during the later Holocene likely was the pony morphotype coupled with a standing mane and the black dun coat colour. The Przewalski-Konik hybrids living in the Lippeaue (go here or here) bear great potential for achieving that with selective breeding. The recessive standing mane and the recessive black dun coat colour can be fixed rather easily by breeding. I do not necessarily suggest that the combination Przewalski-Konik is the way to go for entire Europe. Many local landraces could be crossbred with Przewalski’s horses for “rewilding”. For example, the already established populations of Garranos, Sorraias, Exmoor ponies, Hucule and Bosnian mountain horses could be supplemented by single Przewalski’s horses, most ideally stallions. Surplus animals from zoos could be used so that the population of Przewalski’s horses that is used to preserve the subspecies is not depleted. And as the Lippeaue horses have shown, the introgression of one single animal can have a great impact on the phenotype of the entire herd without affecting Przewalski’s horses preservation efforts. I would pay attention that the genes for a black dun coat colour are always in the mix, as this was the original colour of the late Holocene European wild horse. In the case of the Sorraia, Hucule and Bosnian mountain pony, these alleles would be in the mix. In the other breeds, it might be best to introduce black dun stallions with a standing mane from another location to produce the desired phenotype. 

 

I think Przewalski’s horses should always be in the mix because they represent the last wild horse and the populations in Chernobyl and grazing projects have shown that they do well in the European biome. Alas, most projects will likely pick domestic horses only, because they are easier to handle, easily available, cheaper and there are no legal restrictions. 

 

Literature

 

[1] Sandoval-Castellanos et al.: Coat colour adaptation of post-glacial horses to increasing forest vegetation. 2017.

[2] Fages et al.: Tracking five millennia of horse managment with extensive ancient genome time series. 2019. 

[3] Wutke et al.: Decline of genetic diversity in ancient domestic stallions in Europe. 2018. 

 

 

My trip to the Lippeaue in 2022 (Taurus cattle)

Last week I visited the Lippeaue reserve again, which is the main Taurus cattle breeding site in Germany. As usual, it was a very enjoyable trip, and it was great to see the animals again and how the herds progressed since 2017. 

It has been five years since my last trip to the reserve in 2017. Some of the older individuals have died or had to be slaughtered in the meantime, including Lerida, Dona-Urraca (the Sayaguesa cow with the great horn curvature), Linnet and the huge Laokoon’s brother. Others, like Lamarck, are still in the herd. The other current breeding bulls are new. I counted 98 individuals in the stock list, including the calves. As long-term readers of my blog will know, the Lippeaue population is divided into five herds: Hellinghauser Mersch, Klostermersch-Nord, Klostermersch-Süd, Disselmersch and Kleiberg. There is one breeding bull per herd, selection takes place by picking a breeding bull with desired traits and selecting out individuals. 

 

Hellinghauser Mersch 

 

The current breeding bull at Hellinghauser Mersch is a nameless bull with the number 47 938, which is the son of Laniel and Larissa. Therefore, both its parents are crossbred themselves – this is good, because it’s where the real selective breeding starts. 47 938, as a result of two crossbred individuals that both are very useful, looks good itself. He has a flawless wildtype colour, horns facing forwards in a 60° angle to the snout, the hump is more or less large, and he has a short dewlap. He is three years old, thus not fully grown. 

 

The cow 42 604 is one of my favourite cows. I saw her as a young cow in 2013, and her horns developed considerably since then. Her colour is a flawless aurochs cow colour, and bears striking resemblance to some of the depictions at the Lascaux cave. She is a daughter of Lamarck (Sayaguesa x (Heck x Chianina)), and Julia, a red Sayaguesa cow, thus she is 75% Sayaguesa. In general, Sayaguesa is by far the dominating breed in the Lippeaue gene pool. This is because Sayaguesa simply is a very useful breed that results in good-looking animals. 

 

Another good cow of the same combination but with a different Sayaguesa mother (named Zamora) is 42 630. Like 42 604, she has a perfect wildtype colour and her horns are good as well. 

 

Apart from the wildtype-coloured individuals, there are some other colours as well. There is the cow 55 443, which is one of those with a pink nose and a light coat colour. I think that it is possible that it is the e mutation on the Extension locus, a colour variant that is found in breeds like Highland and Simmental, but I am not sure. This mutation disables the production of black pigment in the mucosa, horn tips and coat colour and is recessive under the wildtype allele. I wonder which breed contributed the colour variant displayed by 55 443, perhaps Heck cattle (Highland is one of the founding breeds of Heck). Basically, it is tried to avoid this colour variant, but 55 443 has good horns and is comparably large, so she is kept in the herd. She is the daughter of Laokoon’s brother (Sayaguesa x (Heck x Chianina)) and Loren, a daughter of Luca and Lirgit. 

 

Another cow with a deviant colour variant is 47 988. Her nose is pink too, therefore she might have the e mutation too, but she also seems to have dilution alleles contributed by Chianina. She will be selected out. 

 

One of the Lidia-influenced individuals is 79 813. She is the daughter of Lamarck and Lepisma, a half-Lidia cow. She is a little bit more nervous than other cows, which is very likely due to the Lidia influence. Her horns are good, the colour is alright as well, and she is from good parents. 

 

Most of the bulls that are born in the Lippeaue are black with a dorsal stripe. Some, however, have a saddle. And a young bull in the Hellinghauser Mersch this year is kind of cow-coloured. He is a son of Laokoon’s brother. I suspect that this is the case because Laokoon’s brother had a saddle, so that the sexual dichromatism is less pronounced in some of the individuals in this herd. 

 

55 444 is another cow with a flawless aurochs cow colour. 

 

Klostermersch-Nord

 

Lamarck is an old boy now, he is 15 years old. He still looks good, he did not grow a massive body. I think his horns even grew a little bit. I still consider Lamarck the best Taurus bull to date, and therefore the best “breeding-back” bull that was born yet, although he is not as huge as Laokoon’s brother. Due to his age, he has become slow and tired, often he is found outside the herd. It’s probably his last year. 

 

Linea is of the same combination as Larissa, namely Chianina x (Sayaguesa x (Heck x Chianina)). She is the daughter of the Chianina cow Eloisa and Lombritz. As she came rather close, we tried to measure her withers height, and the result was 156 cm. For a cow that’s a very good size, most aurochs cows were not much larger. 

 

01 896 is a daughter of Laokoon’s brother and Dunja, so it is an F2 of the combination Sayaguesa x (Heck x Chianina). I think true F2 are very interesting, as they have a higher chance to be homozygous than usual crossbreeds.  

 

55 441 is the daughter of Lamarck and Nadia, the Heck cow from the Steinberg/Wörth lineage, so she is half Heck half Sayaguesa x (Heck x Chianina). 

 

Nadia herself is old now and doesn’t calf anymore. She bore two bull calves which were slaughtered and 55 441. 

 

Klostermersch-Süd

 

Most of the individuals on this photo have the right colour for their sex, so there is good dichromatism in the herd

The breeding bull at Klostermersch-Nord is Laniel. He is the son of the Sayaguesa cow named Augustina and Laokoon’s brother. The horn curvature is really nice and also the hump is comparably large, what compensates the fact that he has a faint saddle. 

 

01 870 is a daughter of Laokoon and Laniana, therefore she has a little bit Lidia in her blood. The colour is flawlessly aurochs-like, and also the horns are good. 

 

Larissa next to a wildtype coloured cow

Larissa is the largest cow in the Lippeaue and the same breed combination as Linea, with the Chianina mother Laura. 

 

Disselmersch

 

The breeding bull at Disselmersch is Darth Vader III, who became famous as the “jumping bull” on Youtube. He is the son of Londo, who was an F2 Sayaguesa x (Heck x Chianina) and the son of Lamarck, and the cow Laniana. He is 1/32 Lidia. 

 

Guessing by eye, the body size and horn size of the animals at Disselmersch is slightly smaller than in the other herds. 

 

Kleiberg 

 

Linnet was replaced as a breeding bull this year, the new breeding bull is Dominator. He is the son of Laniel and a Sayaguesa cow, therefore mostly Sayaguesa. The horns of this bull are great. The curvature is very aurochs-like, and if they continue growing with this curve they will be perfect. The angle between the horns and snout is rather narrow, but that will be compensated by the horn orientation of other individuals. The horns also have a nice size. He will continue to grow for a couple of years, I am looking forward to see how large he is going to get. 

 

Bionade, the Sayaguesa x Chianina cow, is alive and well. Back in 2017, I measured her at 155 cm at the withers, and she must have grown since then, because she is huge. She came rather close, and I was impressed by how large she is. I am looking forward to the offspring with Dominator, his great horns coupled with her large size surely has a lot of potential. 

 

Another very large cow is Kasmerodia. She has the same deviant colour as 55 443 which might be the recessive e mutation, but her large size and the large horns make her a useful individual. She is the daughter of Loren and Laokoon’s brother, therefore she is more Heck than Sayaguesa yet still she is huge. That shows that genetics work by chance, which is always interesting to see. 

 

Kalandra is a daughter of Linnet and Kalidis, a daughter of Bionade. Her horns are comparably large and the colour is aurochs-like. 

 

The most important question is: did the average quality of the individuals increase over the last few years? I think it did, as cows with inwards-facing horns are now much more common than in 2017, 2015 or 2013. Looking at the horns of most of the individuals, the first impression may be that the tips should face more inwards, but actually the curvature is alright, it is just that they should be oriented a bit more diagonal when viewed in frontal view. To explain what I mean, have a look at the photomanipulation of Lerida. I elevated the horns laterally by a few degrees in the "aurochs picture". Maybe it is best to call this the “lateral horn orientation”, in contrast to the horn orientation relative to the snout. I haven’t realized that this is a factor previously. Once the horns are a bit more laterally elevated, the curvature automatically looks more aurochs-like because the tips face more inwards, although the shape of the horns is actually the same. That way, the horns would resemble those of a lot of aurochs skulls, such as the one from the Gramsberger Museum or that at Asti, Italy. I don’t know how to fix that by breeding in future generations, as many aurochs-like landraces have a horizontal lateral horn orientation. All in all I think the horn curvature of most of the individuals is good and has improved over the last years. 

Regarding the sexual dichromatism, most individuals are coloured correctly. Bulls tend to be black with a dorsal stripe, cows tend to be reddish brown. However, there are also black cows and rarely also cow-coloured bulls, so that the dichromatism is often present but not always. 

Concerning the general colour, most individuals have the right colour phenotype. Half-Chianina individuals have a diluted colour of course, as Chianina has several dilution alleles, some of which are recessive. Selective breeding has to purge these alleles from the population in the long run, but considering that colour is regulated only by a few genes, that’s not all too difficult. 

Regarding the morphology, I think the trunk of the cattle is longer than in the aurochs. This is a general problem for “breeding-back”, no matter which project, as in most taurine cattle the trunk is longer than in the aurochs. Only some zebu landraces have a truly aurochs-like short trunk. This is why I included trunk length in my list of the challenges for “breeding-back”. But in general, Taurus cattle are of course more long-legged than Heck cattle, and also slenderer. 

 

All in all, I think the herds are on a pretty good way. I like all of the current breeding bulls and I am looking forward to see how large they will get and what the horns of Dominator are going to look like when he is fully grown in a few years. I was very impressed by the size of Bionade, Kasmerodia, Linea and Larissa. The horn size of many individuals is within the range of the Holocene European aurochs when skeletons like the Himmelev bull are considered. Of course, hypothetically, crossing-in Watussi for example would increase the horn size but it would also introduce a lot of unwanted traits like a large dewlap, the indicine hump, or a small body size. Backcrossing with Chianina would help to increase the body size, but also increase the frequency of alleles for small horns and colour dilutions – therefore, it is always about finding the right balance and prioritizing certain traits. Otherwise, it would be too easy. 

So far, no individual has been born that comprises all of the desired traits (that goes for all the other “breeding-back” projects as well of course). But I think that basically all of the aurochs traits that are achievable with domestic cattle are present in the gene pool, therefore the first of the milestones for “breeding-back” that I have defined years ago has been accomplished in the Lippeaue.

 

The horses 

 

The Lippeaue reserve is also home to the Konik-Przewalski crosses. These are either bay dun with a standing mane as a Przewalski’s horse, bay dun with a falling mane and rarely also black dun with a standing mane. Most individuals are bay dun in colour because they are most likely heterozygous and the a allele on the Agouti locus (resulting in black dun) is recessive under the A allele (resulting in bay dun), therefore bay dun is the dominant phenotype of most of the crosses. So far, no concrete breeding goal for the phenotype of the crossbreeds has been defined. They are wilder in behaviour than Koniks, which are domestic horses, since Przewalski’s horses, being wild horses, are more difficult to handle than the domesticates. The remaining pure Koniks are sometimes sold as riding horses, which is impossible with the Przewalski’s hybrids because of their wild behaviour. Interestingly, I was told that the legal protection status of the Przewalski’s horse in Germany also goes for the hybrids, what surprised me. Some of the hybrids have already been sold to other grazing projects. This could increase the Przewalski’s influence in the Konik in Germany (the Konik already has introgression from the Przewalski’s horse) in the long run, which I consider a good thing. A haplotype typical for Przewalski’s horses has been found in an ancient DNA sample from a European wild horse stallion, what suggests that the range of the two subspecies was continuous. Therefore, Przewalski’s influence in European landraces is not “unnatural”, and also beneficial because the Przewalski’s horse is a genuine wild horse. In the end, the Przewalski’s horse would likely have recolonized Europe from Asia after the extinction of the European wild horse if it had not been for the anthropogenic obstacles. 

All in all, I think the Taurus cattle in the Lippeaue represent the top-level of current "breeding-back", and also the Przewalski's hybrids are very interesting and have potential. Therefore, it is always great to visit the herds and see the breeding progress.