Wednesday, 23 November 2022

Horn size #1: aurochs with massive horns

All in all, the aurochs was a large-horned bovine. The horns were variable in size, also depending on if anthropogenic influence was present or not (I explain that in that post). With this and the upcoming post, I want to cover that variability. This post is going to cover some of the aurochs remains with the largest horns, to show the upper size limit, the upcoming post is going to show the lower size limit. 

 

-) Various B. p. namadicus skulls 

The Indian aurochs was smaller in overall body size than the European subspecies (in the lack of a complete skeleton no withers height data can be given), but had proportionally larger horns. Only a few crania have been published, and I have seen photos of only three with horns. One of them is at the Geological Survey of India, from the Narmada Valley: 

 


The horn cores are rather wide-ranging and proportionally very large, although there are no size data given for namadicus horn cores that I know of. But I have seen a photo of that skull in frontal view, and assuming that the distance between the horns is 20 cm (which is typical for not so large European aurochs bull skulls), the horn span would have been 133 cm. Since I don’t have data for the length of the cores, I don’t know how long they are. But considering that there is no general rule for how much centimetres the horn sheath adds to the length in a bovine, the length of the horns in life can only be guessed anyway. I assume they easily surpassed one metre. 

Another namadicus cranium shows fragmentary horn cores: 

 


As you see, the part of the left horn core that is preserved is roughly the craniocaudal length of the skull, and it is nowhere near starting to curve inwards, meaning that quite a large part of the horn core is missing. This suggests that this specimen had even larger, very large, horns in life. 

 

-) One suxianensis skull fragment 

The skull fragment I am talking about was published in a Chinese paper (Xie Wanming: A skull of Bos primigenius suxianensis from Anhui. 1988). It is shown from several views: 

 


What becomes apparent is that those horns are ridiculously long. I know no measurements for this skull fragment, so I can only estimate. If the distance between the horns was 20 cm (suxianensis was comparable in size to primigenius), the horn span would have been 137 cm. And this is only a conservative estimate as a 20 cm distance between the horns is actually from the smaller end of the size spectrum of aurochs skulls. Other Bos primigenius suxianensisspecimen show comparably large horns too, but this skull fragment stands out. It also deviates from the other suxianensis specimens in having a rather narrow angle between snout and horns, more comparable to the North African aurochs, while the other specimens had a larger angle between horns and snout. 

An important question is how much the keratinous sheath would add to the length of the horns in life. The aurochs horn sheaths recovered vary greatly in the length they add to the bony core, from 5 cm to 33 cm. In any case, the horns of this East-Asian aurochs were very long. 

 

-) The Wadi-Sarrat cranium 

I have only seen two skulls of North African aurochs so far. One has very large horn cores and is the oldest aurochs skull found outside Asia so far, the Wadi-Sarrat cranium. Photos and measurements of this skull can be found in this paper. The left horn core has a length of 112 cm. With that length, the horn cores are actually longer than those of B. buiaensis, which has very wide-ranging horns and thus appears particularly long-horned. And this is only the bony core, with the sheath the horn would be larger in life. Calculating using the photo and the scale bar, the horn span must be 140 cm. 

 

-) The Sassenberg bull 

I used the Sassenberg bull for many full body reconstructions of the aurochs in the past, which I do not do anymore because I was told it is partly a composite specimen (life reconstructions based on this skeleton always looked a bit weird, now I know why). But the skull is authentic in any case, and it has rather large horns. 

 


-) Skulls found near Rom 

Frisch 2010 describes skulls found near Rome, which are notable because of their particularly large horns. One of them has horn cores of a length of 120 cm, which is the largest horn core length I found in the literature so far. Considering that the keratinous sheath can add up to 40% length to the core, it is easily possible that large-horned aurochs had horns of a length of 1,5 m. But without having the sheath we cannot be sure, it is also possible that it added only a few cm. 

 

-) Two skulls found at Stonehenge 

Stonehenge is not only notable for its stone monument, but also because it is an ancient hunting site where about 50 aurochs have been found. I have seen three well-preserved crania from that location, two of which have massive horns. Go here and here. It’s incredible how thick the horn cores of the first skull are, imagining the horn sheath they must have been very impressive in life. 

 

-) The Viterbo skull 

The skeleton displayed at Viterbo, Italy, is a postcranial skeleton with the skull from another specimen because the original skull was deformed during fossilization. The mounted skull of the Viterbo specimen has very thick and large horn cores. 

 

-) The skull fragment from Groß-Rohrheim 

Groß-Rohrheim in Germany is a Interglacial site in Germany where many of the typical Interglacial megafauna has been found, also including many aurochs remains. One skull fragment is notable for having massive – very large and very thick – horn cores. The horn span is, according to the publication listed down below, 142 cm and the diameter is 15 to 16 cm, the length is 103 and 105 cm. Considering the size of the fragment and the dimensions of the horn cores, this specimen must have been an absolutely impressive sight in life. 

 


-) The Faborg skull 

This cranium was found near Faborg in Denmark and is exhibited at the National Museum of Copenhagen, next to the Prejlerup bull skeleton. According to a picture description I found on google, the horn span of that specimen is 114 cm. 

 

-) The possible siciliae skull 

The skull from Sicily that might be of the dwarf subspecies B. p. siciliae shows very long and wide-ranging horns. Since the overall body size of the animal was small if it really was from the dwarf subspecies (which had a withers height of only 130 cm), it is questionable if the absolute size of the horn cores is as impressive as in the those from the mainland subspecies, but proportionally they are very large. 


 

Looking at the largest-horned aurochs, it can be concluded that Bos primigenius was among the largest-horned bovines that would be around today if it had not been for anthropogenic influence. Only those of the wild Asiatic water buffalo are larger among extant bovines. 

It has to be noted that these specimens I presented here are only the tip of an iceberg, and it is hard to say what was “average” for the aurochs, and if there were differences between the subspecies. The point of this and the upcoming post is to show the extreme ends of the horn size spectrum. The next post is going to focus on small-horned aurochs. As a little spoiler (or teaser): they all have something in common, something that might reveal why their horns were small compared to the huge horns of the specimens presented in this post. 

 

Literature 

 

Van Vuure, 2005: Retracing the aurochs – history, morphology and ecology of an extinct wild ox. 

Frisch, 2010: Der Auerochs – das europäische Rind. 

Von Koenigswald & Menger: Ein ungewöhnlich großer Schädel vom Auerochsen (Bos primigenius) aus dem letzten Interglazial von Groß-Rohrhiem bei Darmstadt. 2002. 

 

 

Saturday, 5 November 2022

More than 200 genes were involved in yak domestication

This is not exactly news, but from a paper I only discovered recently. It’s by Qiu et al. from 2015 and reports that 209 genes were found to be likely involved in the domestication of the yak about 7000 years ago [1]. 

Of these 209 genes, more than 30 are associated with brain and neuronal development, 19 other genes with behaviour and only a few genes with physical appearance and economically relevant traits [1]. 

This could provide insights to the question how many genes were affected in the domestication of cattle, which would tell how many genes would have to be edited in order to recreate the aurochs with genome editing. It makes a difference if one would deal with 20 genes, or 2000, for technical and practical reasons. Considering the findings from yaks, the number of genes where aurochs and cattle differ might at least be in the three-digit area. It has to be kept in mind that yaks are not nearly as strongly domesticated as highly derived cattle breeds. Basically all yak breeds are landraces, and gene flow from the wild populations into the domestic yak has never ceased to occur [1]. 

 

[1] Qiu et al.:  Yak whole-genome resequencing reveals domestication signatures and prehistoric population expansions. 2015. 

 

 

Sunday, 16 October 2022

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. 

Thursday, 29 September 2022

When and how should the "breeding-back" projects cooperate?

Today in the 2020s, there are several “breeding-back” projects focusing on the European aurochs. I think that there can be no question that it would be most beneficial for “breeding-back” as a whole in order to achieve the goal – that is, a population of cattle that is as aurochs-like and at the same time as genetically diverse as possible to be fit for a reintroduction into Europe’s nature – if the projects would one day cooperate in some sort. The question is: when and how should the projects cooperate? 

First of all, it has to be visualized why cooperating between the different “breeding-back” projects would be beneficial. It would be helpful to maintain a higher level of genetic diversity than if the projects would work separately. Maintaining a certain level of genetic diversity while at the same time creating a homogeneously aurochs-like population is one of the challenges of “breeding-back”. This is less of a challenge when there are several projects that cooperate. When the crossbred cattle used in the breeding projects are bred selectively for a more homogeneous phenotype, some alleles become fixed. In the process of homogenizing the population, the genetic diversity is reduced. However, in each different project, different alleles become fixed. And when the populations of the projects are eventually combined to one large gene pool, the genetic diversity is larger than it would be if there was only one project. As an example, Project 1 has a cattle population with the alleles A, B, C and D on loci responsible for any trait that is not affected by the breeding objectives of “breeding-back” but relevant for genetic health. Project 2 has a cattle population with the alleles E, F, G, and H. Both projects establish a homogeneous aurochs-like phenotypes, and reduced their genetic diversity in the process. In Project 1, only the alleles B and D remained in the populations, being present homozygous now. D is deleterious when homozygous. In Project 2, only the alleles F and H remained in the now very aurochs-like animals, and allele F is deleterious when homozygous. So both projects achieved a very aurochs-like phenotype at the expense of genetic diversity. When both projects combine their gene pools into one large gene pool, we have a population with the alleles B, D, F and H. Now the allelic diversity is larger again and the number of individuals being homozygous for deleterious alleles dropped significantly and since both projects have very aurochs-like animals, the degree of aurochs-likeness was not affected by combining the two lineages. This is of course a simplified example, but combining two or more lineages always results in a greater allelic diversity and if all the individuals of those lineages are very aurochs-like, genetic diversity would not go at the expense of resemblance to the aurochs, which would be the case if a not related non-“breeding-back” breed was crossed in to increase the genetic diversity. 

While combining the different “breeding-back” lineages would be beneficial in the long run, it does not make sense if the different projects are yet at different levels of “breeding-back” progress. For example, if one project has great animals and another project is just starting or has animals of modest resemblance to the aurochs, and they exchange animals, the result being one project benefiting in terms of aurochs-likeness and one project perhaps introducing undesired traits from the breeds of the other projects, while the genetic diversity would not necessarily increase because the process of achieving very aurochs-like animals is not completed yet. Rather it could lead to the contrary, because the project with the less good animals will use the great animal from the other project on a larger scale in order to improve the aurochs-likeness of their animals, thereby narrowing its genetic diversity. Thus, I think exchanging animals between the “breeding-back” projects really only makes sense if all of them are at the same level of aurochs-likeness. 

When one project has an animal with a trait that all the other projects lack, for example if one project has absolutely perfectly aurochs-like horns and all the animals of the other projects have bad horns, it certainly would be beneficial for the aurochs-likeness of the other projects to acquire animals from the project with the perfect horns, but it would also narrow the genetic diversity in all of them. Therefore, it would be smarter before exchanging animals to ask the following questions: Why are the animals of the other project better in this respect? Did they use a breed that contributed the traits that are lacking in the one project, and could this or another breed with that trait be used in the project? For example, if one project used only medium-sized breeds as founding breeds, and another project included a very large breed and thus has larger animals, it would be the best decision for the overall genetic diversity of the “breeding-back” pool to cross-in very large founding animals instead of depleting the diversity by using an individual from the other project. 

Therefore, I think that for now, the different “breeding-back” projects should focus on their own gene pool and how they can improve the aurochs-likeness of their animals within the gene pool. That is not to say that never ever should individuals, cows in particular, be exchanged between the projects. Only the large-scale use of individuals from other projects, f.e. as sires for many years, however aurochs-like it may be, should be avoided so that the overall genetic diversity is not reduced. But once all of the projects achieved the same level of aurochs-likeness, i.e. that all of the animals of all of the projects are large, have the right colour, the right horns, the right sexual dimorphism, the right morphology et cetera, I suggest to exchange animals at a regular basis in order to create genetically diverse and healthy individuals. In zoos and reserves, the animals are exchanged on a regular basis in order not to diminish the genetic diversity of the herds, and “breeding-back” should do so as well once all projects have reached the same level of quality. The result would be one large and genetically diverse population of very aurochs-like cattle that are fit to be established in European wildlife reserves. 

 

 

Monday, 12 September 2022

An animation of an aurochs running

I have not seen an anatomically correct animation of an aurochs yet, so I decided to try one myself. I made a little video of an aurochs bull running. It was done by making animated GIF consisting of 16 drawings of the same individual during running, based on a GIF of an American bison running. I converted the GIF into a video, and here is the result: 



Friday, 2 September 2022

Should we allow paraphyletic genera?

This post is a rather theoretic one, and some might wonder what it has to do with the main topics of my blog. However, the question if we should allow paraphyly in some cases in taxonomy is relevant for the naming of species, some of which are in the focus of this blog. 

For those who are not familiar with the term “paraphyletic”, it describes when a group is not a natural group in the phylogenetic sense, a group that has a common ancestor but does not include all descendants of this common ancestor. Paraphyletic groups are avoided in modern taxonomy because treating them as if they were the same as mono- or holophyletic groups (such that have a common ancestor and include all of its descendants) is comparing apples to bananas. To illustrate that, I take my favourite vertebrate group as an example: dinosaurs (I am actually quite a big fan of Mesozoic paleontology ever since I was a kid). It is nowadays very well-established that birds descend from non-avian dinosaurs, so that they are part of the Dinosauria clade. Why? Because Velociraptor is closer to birds than Tyrannosaurus, and Tyrannosaurus is closer to birds than a Triceratops. If birds weren’t dinosaurs, Velociraptor isn’t a dinosaur either. But in this case, Tyrannosaurus would not be a dinosaur either, because it is closer to birds and Velociraptor than to Triceratops. And so on. Consequently, birds are dinosaurs because they are nested on the dinosaur branch of the phylogentic tree. Dinosaurs themselves are part of what has traditionally been called reptiles. That means that birds should be reptiles, because birds are dinosaurs. That sounds crazy when comparing a lizard with a duck, but that’s evolution. A crocodile is closer to birds than it is to lizards, and a Tyrannosaurus is closer to birds than a crocodile. Thus, the group of reptiles in the classical sense is not a natural group because there is that decision to regard some members of this clade not as members of this group for historical reasons that go back to the time of Linnaeus. This is called paraphyly. Therefore, Reptilia is not the same as Aves (an impression that can be created by the traditional rank system of four tetrapod “classes”), rather there is the Sauropsida clade, that includes a common ancestor and all its descendants, living and extinct. On this clade, there is the Aves clade, which includes all birds. Reptilia, however, is not a clade. It is a collective term for all sauropsids that are not birds, including not very bird-like animals such as lizards, and extremely bird-like animals such as Velociraptor mongoliensis. Since paraphyletic groups make the taxonomical system much more arbitrary than it already is, they are discarded in the modern (phylogenetic) systematics, otherwise one would compare apples and bananas. Systema naturae came 101 years before Darwin’s On the Origin of species and our knowledge of extinct organisms. 

Another problematic reminiscence of the original taxonomy that came before our knowledge of evolution are “ranks” for clades. That is the hierarchical system of species, genus, family, order, class and so forth. Nobody was ever able to define these ranks objectively and universally – how can we know that Hominidae, Tyrannosauridae and Canidae are of the same “rank”? There is no definition. Aves, for example, is considered one of four tetrapod “classes”, descending from reptiles, which were considered a “class” themselves. Now we know that Reptilia is not a natural group and most researchers use the name Sauropsida instead, but Sauropsida and Aves cannot both have the same “rank” as Sauropsida is a much more inclusive group. The same problem exists with any rank. For example, the Raphidae (dodos and its close relative Pezophaps solitaria) was downgraded to a subfamiliy (Raphinae) because it is obviously nested within the Columbidae (pigeons), so both cannot be the same “rank”. Therefore, “ranks” make taxonomy even more arbitrary and only worked back in Linnaeus’ time when we had no knowledge of evolution and extinct animals (as a side note, I wonder if Linnaeus would have questioned his own system if he would have had the possibility to classify living Velociraptor or Brachiosaurus, which are obviously between the “classes” of reptiles and birds in his understanding). “Ranks” for clades are not considered to be of any factual relevance in modern systematics anymore. 

This brings us to genera, which are ranks as well. However, genera cannot simply be ignored as they are perpetuated by the binominal nomenclature in biology. Each name for a species is composed of a genus epitheton and a species epitheton. Some species share the genus epitheton because they are considered members of the same “genus” (for example Panthera leo and Panthera tigris). A genus is based on a type species, and all the other species are assigned to that “genus” when they are considered “similar enough” to the type species to be considered members of the same “genus”. The problem is, however, nobody ever defined how to measure this similarity objectively and universally and how much of that measured similarity is “similar enough”. At least not that I am aware of. But we would need something like that in order to create a consistent concept of a “genus” that is necessary because it is relevant for the naming of species. The perception of what is “similar enough” also shifts with time. Back in the 18th century, a “genus” was about as inclusive as is a “family” is nowadays – at least in some cases (take elephants: back in the 18th century, there was Elephas maximusElephas africanus and Elephas primigenius, which are nowadays considered three different genera, ElephasLoxodontaMammuthus). If that was not problematic enough, there is the evolutional process going on. Species evolve into new species, the phylogenetic tree continues to grow. And as a consequence, there is inevitably the case that one genus evolves into another. On the cladogram, the resulting “genus” is paraphyletic. For example, the Haast’s eagle Harpagornis moorei is nested within the “genus” Hieraaetus, the two Bison species nest within the “genus” Bos. But saying “that genus is paraphyletic” may be not entirely correct, as a “genus” is not a clade but a “rank” that is often congruent with a given clade. A genus is defined as all species that are “similar enough” to the type species and the type species itself. Nobody defined a “genus” as a clade, so it cannot actually be paraphyletic. So, is Harpagornis moorei “similar enough” to the type species of HieraaetusHpennatus? Are Bison bonasus and Bison bison similar enough to the type species of BosB. taurus/primigenius to be considered members of that genus? The answer is entirely subjective, and there is no way to objectively and consistently measure “similar enough”. Perhaps Harpagornis moorei is more distinct from Hieraaetus pennatus than Bison bison is from Bosprimigenius. Including Harpagornis moorei into Hieraaetus means that also a hypothetical descendant of H. mooreiwould have to be included into Hieraaetus because it nests on this clade. That means that till the end of all days all species that would have evolved from Harpagornis or another member of the Hieraaetus clade, however distinct from the Hieraaetus type species they may be, have to be included into the “genus” Hieraaetus to avoid paraphyly. And considering that each genus descends from another genus, right down to the last common ancestor of all organisms classified under the rules of the ICZN, all animals are necessarily members of the same, ancestral “genus”, if a paraphyletic “genus” is to be avoided. That means that all genera are essentially synonymous. This makes the concept of a genus meaningless, if we are consistent with the approach that a “genus” should never be paraphyletic. But a “genus” is a rank and not a clade, and ranks are based on arbitrary subjective decisions based on similarity to a defined type species, and not on clades. They are often congruent with clades, yes. And regardless of how we name the species, Bison bison is a member of the Bos clade, and Harpagornis moorei is a member of the Hieraaetus clade (by the way, the same problem also goes for species. There is no definition of a species that works universally, but if we look at the individual level, all species in the history of evolution are paraphyletic on a cladogram, because some individuals assigned to the ancestral species will necessarily closer to the new species than to the earliest member of the ancestral species. Looking at the time scale, the concept of a species is artificial and arbitrary, and species are definitely not clades). Another way to avoid genus paraphyly instead of lumping is splitting. For example, Loxodontaafricana and Loxodonta cyclotis are “similar enough” to be considered a member of the same “genus”. But it turned out in recent genetic research that L. cyclotis is actually closer to Palaeoloxodon than to L. africana. How to avoid the paraphyly? If L. cyclotis is not “similar enough” to Palaeoloxodon, it might be assigned to its own “genus” because it is closer to Palaeoloxodon, but not similar enough to be a Palaeoloxodon species. That might work when looking only at Loxodonta and Palaeoloxodon. But all genera evolved from another genus. There will always be species that are closer to the descending genus than to the type species of a given genus. As a consequence, each species would end up with its own genus, making the concept of a genus moot. So, both approaches to avoid genus paraphyly, both lumping and splitting, would, when applied consistently to all organisms, make the genus as a rank useless – the problem is more fundamental, because a rank is treated as a clade here. 

So, considering that the concept of a “genus” as a rank is arbitrary and subjective, and the concept of a “genus” as a clade makes the term absurd because all living organisms would either be members of the same ancestral genus or each species would be its own genus so that no genus is paraphyletic, what should we do? At the moment, the way it is, it is inconsistent. See the example with Harpagornis. The concept of a genus, however, is tied to the binominal nomenclature. If we change the binominal nomenclature, we will have to change the names of millions of organisms. And naming a species with two words is more definite than just one word. But we could do something intermediate: erecting a new first epitheton for each species that is not a type species of an already existing “genus”. That would also be a lot of work, but it would be more consistent and compatible with the evolution of species and the cladistic system. In some cases it would work easily, when the species epitheton is a latin name on its own. Take Panthera as an example. I was unable to find out what the type species of Panthera is, but it would work in all five species: ParduspardusLeo leoTigris tigrisOnca oncaUncia uncia. Taking the Bos clade, it would work as well, because a number of synonynomous genera or subgenera have been erected or some species epitheta are just a latinized version of the name of the species: Bos primigeniusGaurus gaurus (gaur), Bibos javanicus (banteng), Novibos sauveli (kouprey), Poephagus mutus (yak), Bonasus bonasus (wisent, bonasus is just another name for bison, by the way) and Bison bison(American bison). For a lot of species, new first epitheta would have to be erected, especially for fossil taxa. That would be a lot of paperwork, but let us be honest, each scientist dreams of naming a new taxon, so that “Name, Year” will be mentioned next to the name forever. So, I think that many would not mind and take that opportunity to immortalize their own name by naming a new taxonomical name. And since it is not the description of a new genus that includes several species and has to be differentiated from other genera, no profound diagnosis is necessary because the species it refers to already has been diagnosed. 

I know that this is a radical approach, and it would take decades until it is established and the rules of the ICZN would have to be changed. But it would be consistent, less arbitrary, and compatible with evolution. As already mentioned, Linneaus came 101 years before Darwin, and taxonomy has already reacted by discarding paraphyletic groups. Maybe the next little revolution that is necessary to transfer taxonomy into the 21st century is to abandon the concept of a genus. The alternative is, if taxonomy is supposed to be consistent, to allow “paraphyletic” genera (which are not really paraphyletic since they are not clades). 

 

Monday, 22 August 2022

How large were the largest aurochs?

The size of the European aurochs has been both over- and underestimated. The largest size estimate given in the literature I have seen so far was 230 cm at the withers (I don’t remember the source, unfortunately), the smallest for bulls was 145 cm. The latter is definitely inaccurate, as there is no evidence for European aurochs bulls with a withers height noticeably below 160 cm. But what was the upper size limit of aurochs bulls? 

 

The preserved skeletal material is the only reliable indicator for the size of the aurochs available as no living aurochs were measured. Complete skeletons are considerably rarer than finds consisting only of fragmentary material or single bone elements, but they are the better indicator for the size of the animal in life. But in order to give an accurate idea of the size of the living animal, it has to be mounted anatomically correct. Alas, most skeletal mounts of the aurochs have anatomical flaws. These flaws can make the withers height of the skeleton smaller or larger, depending on what is wrong. The Prejlerup bull skeleton, however, is mounted fairly correctly. I was unable to find a reliable source on the height of the skeleton. Using a photo of the skeleton in profile view with a person next to it whose height I know, I calculated the withers height of the skeleton and it turned out to be around 190cm. This is the largest size for a complete aurochs skeleton that I know of. However, it must be considered that the skeleton lacks the soft tissue surrounding the bones, so that the skeleton appears smaller than the individual was in life. For example, the intervertebral discs add quite a few centimetres to the length of the skeleton. The connective tissue between the leg bones adds to the height of the skeleton. The hooves alone might add 2 to 3 cm. And lastly, the skin and fat tissue adds one or two more centimetres. Therefore, it is not unlikely that the Prejlerup bull was 5 to 10 cm taller in life than its preserved skeleton. Thus, the bull might have been 195 to 200 cm tall at the withers in life. 

The Prejlerup bull is the largest complete skeleton from the European aurochs, but probably not the largest specimen found so far. Unfortunately, these specimens are not known from complete skeletons but from fragmentary, isolated remains. The perhaps largest European aurochs found is the London skull, exhibited at the British museum of London, which reportedly has a length of 91,2 cm [1]. This is very large, also compared to other aurochs specimens. The skull length in the other skulls observed by Nehring 1889 was between 64 and 72 cm [1]. Unfortunately, I do not have access to the original source by Nehring, so I don’t know if he specified what he means by “length” in his work – the length from the caudal end of the neurocranium to the cranial end of the nasal bone or to that of the premaxilla? I am cautious considering the huge size of the given length and assume it is from the end of the neurocranium to the premaxilla. This is still very large. 

How large was the animal that belonged to the London skull? In the lack of a complete skeleton, there is no other possibility to get an idea of the total body size than to extrapolate the size based on complete skeletons of other bulls. I used photos of four bull skeletons (Prejlerup, Vig, Sassenberg, Store-damme) in clear profile view and started to calculate. At first, I calculated the absolute skull length of the skulls of the skeletal mounts that I know the withers height of, the Sassenberg (165 cm), Prejlerup (possibly 190 cm) and Store-damme (175 cm) specimen in order to check if the calculation is plausible. The results were a skull length of 79 cm for the Prejlerup, 71,5 cm for the Sassenberg and 70,3 cm for the Store-damme skeleton. The latter two are in accordance with what was found by Nehring, the Prejlerup is slightly larger but the whole skeleton is larger than the other two. So the calculation results in plausible skull sizes for the given skeletons. The relation of the skull length to the withers height was 2,4 in the Prejlerup, 2,307 in the Sassenberg and 2,49 in the Store-damme and Vig specimen. Those are very similar values, the Sassenberg bull has the proportionally largest skull, but it has to be noted that it is partly a composite specimen. Under the assumption that the proportions of the London specimen were comparable to the other specimen, I calculated the possible withers height for the 91,2 cm long skull. The results were: 

If the proportions were identical to that of the Prejlerup bull: 218,4 cm

If the proportions were identical to that of the Sassenberg bull: 210 cm 

If the proportions were identical to that of the Store-damme and Vig bull: 226 cm 

If the proportions were intermediary between those of all four: 220,1 cm 

These are very large sizes. But we simply have that skull that was about 28% larger than what was found to be the average by Nehring 1889 – unless Nehring’s 91,2 cm for the London skull are inaccurate. However, I do not know Nehring’s sample size and if his sample was representative of aurochs from the northern half of Europe (which the other skeletons and most likely the London skulls were), and if all of the examined skulls were from males as females were smaller. There is at least one skull that might be comparable in size to the London skull, the Berlin skull. I saw this cranium two times, and I can firmly tell, it is huge. I don’t know if anyone measured that skull, however. But assuming the Berlin skull is of the same size or a similar size as the London skull, are the results of my calculation plausible? 

Well, there are several possible error sources. 

1. Nehring’s 91,2 cm for the London skull are inaccurate 

2. The bull that belonged to the London cranium might have been oddly proportioned, i.e. with a head larger than usual for aurochs 

3. The photos I used might not reflect the natural proportions of the skeletons (I think they do) 

4. The measurements I took from the photos might be inaccurate or imprecise (in this case, the resulting absolute skull sizes for the skeletons would not be plausible, but they are) 

5. The four specimens do not reflect the variation in proportions within the European aurochs (since the values for the relative skull length are all very similar, except for the one specimen that is partly a composite, I do not think this is necessarily the case). 

The results of these calculations would certainly be more accurate if I had the possibility to take measurements from the actual bones, which I don’t have. But is a size between 210 and 226 cm for the largest aurochs plausible? Large wild yaks reach sizes up to 205 cm, gaur bulls 220 cm, and the extinct Bos (Bisonlatifrons is said to have had a withers height of 230 cm. It must be considered, however, that these species have different proportions and longer spinal processes, resulting in a larger withers height. Thus, I am cautious. But I consider the 210 that result from calculating with the Sassenberg bull actually plausible for the largest aurochs. What would definitely be necessary is a) someone has to measure the London skull and Berlin skull to see if they really exceed 90 cm b) other suspiciously large aurochs bones, such as limb elements, pelves etc., should be checked – if they are by one fifth larger than the same elements from the complete skeletons, that is another hint that there were aurochs larger than 200 cm. However, extrapolating the size of an animal based on single skeletal elements is very risky in general. On the other hand, the London skull and the Berlin skull are noticeably larger than the skulls from complete skeletons which we know how tall they are. We need more complete material of very large aurochs to be sure how large they actually were.  

 

Literature 

 

[1] Frisch, W.: Der Auerochs – das europäische Rind. 2010. 


Sunday, 14 August 2022

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

In the previous post, I wrote that wild-caught Przewalski’s horses from the 19th and early 20th century displayed more colours than the modern population does after the genetic bottleneck in the middle of the 20th 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 20th 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 20th 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. 

Saturday, 13 August 2022

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 20th century. Photos and descriptions of individuals prior to the genetic bottleneck event from the late 19th century and early 20th 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 20th 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 20th century [1]. These horses lacking pangare must have had the non-pangare allele Panp. 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 19th 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 20th 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 20th 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 Urwildpferd1996. 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. 

Thursday, 4 August 2022

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

 

 

Tuesday, 26 July 2022

That Nei distance chart

In 2015, Rewilding Europe published a PDF with a Nei distance chart showing the purported distance of 34 European cattle breeds to the one resolved aurochs genome. Many thought that we finally know which cattle breeds are genetically closest to the aurochs. But interpreting the chart that way would be a huge oversimplification and, in my opinion, inacurrate. In fact, I think we do not know anything more now than we knew before the Nei distance chart. With this post, I want to give my reasons for why I think that. Mind that I am not a geneticist, so this is completely my own interpretation. Critique is much appreciated.  

The Nei distance chart published by Rewilding Europe

1. The Nei distance analysis looked at only a very small fraction of the genome 

 

The cattle genome has 3 billion base pairs, the Nei distance analysis looked at 700.000 base pairs. Precisely, the analysis studied single nucleotid polymorphisms (SNPs). 700.000 SNPs is certainly a lot, but only a very small fraction of the total genome, thus it does not tell us much about the genetic closeness of the cattle breeds to the aurochs. With another 700.000 SNPs the results could be completely different. 

 

 

3. Only one aurochs genome was used for the analysis 

 

We have only one resolved complete aurochs genome for now, which is a problem for trying to analyse the genetic closeness of cattle breeds to their wildtype. It is unlikely (or actually impossible) that one individual comprised the full genetic diversity found in the wildtype populations, thus there must have been wildtype alleles found in other aurochs but not found in this one particular individual. The problem is that these wildtype alleles would be considered domestic alleles if found in a modern cattle individual and not found in the one aurochs individual that had its genome resolved. It could be the case that Caldela, a breed scoring very low on the chart, actually has a lot of wildtype alleles that just happen to be from other aurochs individuals than that of the one genome that we have, and so it results scoring low in the chart. That relativizes the relevance of the Nei distance analysis considerably. 

 

4. Nei distance might not be the ideal tool for analysing the situation of aurochs and cattle 

 

The Nei distance was developed for populations that diverged by mutation and genetic drift in isolated populations. But this is not the scenario that happened in the case of aurochs and cattle. In the domestication of cattle, we have at first drastic genetic bottleneck (since modern domestic cattle go back to only about 80 female founders), then massive directive selection (selection on tameness and economic value) during which many wildtype alleles might have been lost and mutated (= domestic) alleles became fixed, then we have local introgression from different types of aurochs in different regions of the world into the cattle genome (in Africa and Europe at least). Not to forget the not uncommon intermixing between taurine and indicine cattle, which descend from two rather divergent aurochs subspecies. 

 

That is why I have covered the Nei distance chart in only one post on my blog till now. I think it does not tell us much about the actual genetic distance between the aurochs and domestic cattle breeds. That is why the score in the chart seems to be rather coincidental and there is no correlation between a less-derived phenotype and the purported genetic closeness to that one aurochs individual analysed in the chart. For example, Fleckvieh scores higher than the Spanish fighting bull. Of course, it can be possible that a breed that has a rather derived morphology shares more alleles with the aurochs than one with a less-derived morphology, since many of the differences between aurochs and cattle might be non-visible, for example immunology, development, endocrinology, neurology, metabolism, or physiological aspects. But I consider it highly unlikely to be the case with Lidia and Fleckvieh, because Fleckvieh has experienced far more intense selective breeding than the Spanish fighting bull. Their score in the Nei distance chart is not evidence for that either, as outlined above. 

Furthermore, which aurochs are “the aurochs”? Even if we only care about the primigenius subspecies it is complicated to give an answer to that question. British cattle landraces have been found to share nuclear alleles with the British aurochs, likely due to introgression, which we cannot expect for Iberian, Italian or Near Eastern breeds and vice versa. 

Also, the total genetic closeness to the aurochs does not tell us which alleles are present in which breed, which is crucial information if one wants to unite aurochs alleles in one population with selective breeding. A breed scoring low in the overall genetic closeness to the aurochs might have alleles which all the other breeds do not have, and this is exactly the case in this Nei chart: Nelore, as an incidine breed, will share alleles with the British aurochs which taurine cattle have lost, because this is what was found by Orlando et al. 2015 (by the way, if the Tauros Programme is indeed aiming for breeding for “aurochs alleles”, why aren’t they breeding with zebus? There is no other way to get these alleles into the population. The answer is: Because they are not breeding on a genetic level, contrary to what they claim in press releases…). 

Thus, I think that this Nei distance chart does not tell us anything of value for “breeding-back”. Why did the Tauros Programme conduct this analysis, then? I think that’s because they needed to publish something “genetic”, in order to back up their claims that they are breeding for aurochs-like genetics. The project was very content with the results of the chart. They claimed that the breeds used in their project were particularly high-ranking. As you can see in the chart (the Tauros Programme breeds are those written in bold), this is not necessarily the case. Their breeds seem to be rather evenly distributed along the chart. However, this is not relevant for “breeding-back” anyway, at least in my opinion, for the reasons outlined in this post. 

 

Literature

 

Orlando, L.: The first aurochs genome reveals the breeding history of British and European cattle. 2015. 

 

Thursday, 14 July 2022

Heck cattle at Oostvaardersplassen develop aurochs-like horns

I have made a couple of posts about the possible changes in horn shape in the Heck cattle in the Oostvaardersplassen reserve. Recently, I found some new photos of a group of young bulls in the reserve that all show interesting horns from March this year. You can see the animals here

Not only are the horns interesting, the bulls are also much more long-legged and less massive than Heck cattle found in zoos (which is were they descended from). Morphology can be influenced by phenotypic plasticity, so these changes in body shape and proportions do not necessarily indicate a genetic change in these cattle. In the case of the horns, however, I see no way how phenotypic plasticity can influence the horn curvature and orientation relative to the snout, thus I think we see genetic changes here. A change in allele frequency as a result of natural selection is the population genetic definition of evolution. Thus, we might see evolution at work here. 
In how far are the horns of these young bulls different? For once, they face clearly forwards in a 70 to 60° angle relative to the snout, which is identical with the horn orientation of the European aurochs. Earlier Heck cattle from the reserve (which can be seen on older photos easily available on the internet) never have forwards-facing horns, at least not on the photos I have seen so far, which are quite a lot. Furthermore, while the horns of early Oostvaardersplassen Heck cattle are curved rather straight, the horns in these bulls are curved more clearly. They do not curve inwards as strongly in the aurochs by far, but a tendency of the horn tips to grow a curve is there. This can also be seen, even more clearly, in some of the cows in the reserve (the photos aren't online anymore, unfortunately). To me, this suggests that the horn shape of the Heck cattle in the Oostvaardersplassen reserve is evolving. Precisely, evolving to a more aurochs-like horn shape. 
This is not surprising, as the horn shape of the aurochs probably had a purpose. Their strong inwards-curve enabled the bovine to push and pull the opponent during a fight, and the fact that they faced forwards and not upwards or downwards was likely functionally advantageous as well. If the horn shape of the Heck cattle in the reserve is indeed evolving, which can only be proven by gathering photos of individuals from the early years till today, it would endorse the following thoughts: 
1. the horn shape in cattle/aurochs has a function and the horn shape of the aurochs was not a coincidence
2. This has an impact on the evolutive fitness of the individuals (the more functionally advantageous the horn shape the higher the likelihood to win an intraspecific combat for breeding rights, feeding grounds etc.)
3. Eventually, the wildtype horn shape will develop in a cattle population that is exposed to natural selection, especially intraspecific selection 
The more genetically diverse the population, the faster the changes evolve (Fisher's fundamental theorem). Since Heck cattle is a mosaic breed based on many different cattle breeds, the wide range of phenotypes displayed by the individuals might have enabled the adaption process to become visible quite fast. 
I postulated that natural selection will make a variable cattle population in the wild more aurochs-like because wildtype traits are functionally advantageous multiple times on my blog, and I think these recent photos of Heck bulls at the Oostvaardersplassen reserve endorse this idea when you compare them with earlier individuals of the same population. In my opinion, the Heck cattle at this reserve are a valuable example for dedomestication. 
It is no secret that the original founding population of the Heck cattle at the Oostvaardersplassen, being ordinary Heck cattle from various locations, were not prime examples for aurochs-likeness. Yet, natural selection produced at least partly aurochs-like horn phenotypes after 40 years of intraspecific competition. This fits my idea that natural selection will "refine" any "breeding-back" product once released into the wild - if it worked on the mediocrely aurochs-like founding population of Oostvaardersplassen, imagine what kind of phenotypes might be produced by 40 years of natural selection with more aurochs-like cattle. 

Wednesday, 6 July 2022

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 20thcentury. 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.