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Wild Horses
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Updated 29.3.2018 to include more research!
Please note I published this under a noncommercial Creative Commons license. Feel free to share if you find it useful or interesting!

This is a chart on the possible colours of Eurasian wild horses or tarpans (Equus ferus ferus) - a surprisingly varied population, as shown by ancient dna and cave art. These animals only went extinct around year 1900.

Depicted is a selection of possible combinations of the alleles known to have been present in wild tarpans. According to the data set of Pruvost et al. (2011), the most common colours were bay dun, grullo, and spotted bay dun - marked with blue circles in this chart. All these seem to be also depicted in European cave art. According to Imsland et al. (2016) the dun allele was also polymorphic in wild horse population, causing some individuals to be darker than others.

Different combinations would have necessarily occurred from time to time, when horses of different colours mated. The Lp allele, producing leopard spotting, is affected by a large number of modifiers, only one of which of which have been tested on ancient horses. That was only in domesticated Botai horses (Gaunitz et al. 2018). I depicted a variety of possible outcomes of it, but it's impossible at the moment to be sure which spotting patterns were really present.

The letters underneath each horse refer to their alleles. These four were polymorphic in the tarpan population:

Agouti locus
A - dominant allele causing brown coat
a/a - recessive allele causing black coat

Extension locus
E - dominant allele enabling black in coat and mane
e/e - recessive allele preventing black coat and mane (result being a chestnut horse)

Dun locus
D - dun, a diluting factor present in wild horses and asses. Causes lighter coat colour and primitive markings (two-coloured mane, stripes etc.)
d1/d1 - recessive allele causing non-dun colour (black, bay, or chestnut, depending on the base colour). Leaves some primitive markings visible.

Leopard / varnish roan locus
lp/lp - no leopard complex, no spots
Lp/lp - leopard complex, spotted
LP/LP - leopard complex, mostly white. There is a night vision defect associated with homozygous animals, probably making them vulnerable to predators.

I had to assume this one, since genetic test for it was onlt developed in 2016 and it hasn't yet been widely tested on ancient horses:

PATN1 - patterning factor, causes leopard spots with LP

References:
www.pnas.org/content/108/46/18…
www.nature.com/articles/ng.347…
science.sciencemag.org/content…
onlinelibrary.wiley.com/doi/fu…
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I like your drawing. I have only one note: Chestnut base colour dit not occur until very early in the domestication process.
The originally wild horse base colours were black (originally only in Iberia, later also in Central and Eastern Europe) and bay (all over Europe)

The only genetically proved pattern is indeed leopard. The Lp gene has also been found in the 5,500 year old remains of the Botai horses, which were the domesticated forefathers of the Przewalski horse. It could have been introduced by predomestic cross breeding or intentional cross breeding with the wild ancestors of domestic horses, or it was present in the common ancestor of both lineages. In current Przewalski horses there is no trace left of the Lp gene.

The Dun gene and the Pangaré gene are not identified as of yet. But it is likely that these genes would both have been present among wild horses, since these two patterns are also found in the feral Przewalski horse, and since the wild ancestors of the Przewalski horse and the modern day domestic horse lineage share a common ancestor. There is a 1617-bp deletion on chromosome *8*, which prevents the development of a wild-type dun coloration though. Notably, this deletion has been documented in a 43K-year-old horse from the Taymyr Peninsula in Central Siberia.

Pangaré may have been present in wild horses as well, since it is found in several ancient horse breeds, such as Exmoor horses, Yakut horses, Fjord horses and Przewalski horses and would have functioned as a protective countershade. Based on ancient cave drawings not all wild horses in Europe had this colouring, and no ancient remains have been possible to test for such gene yet. The primitive Hucul horses, Pottoka horses, Retuerta horses and Konik horses for example do not posses these markings.

The recovered 26,000 year old remains of the Yukon horse had long hanging, light /blond coloured manes, with pangare and  bay body colour with an dun line on it's back, and black/darker legs than it’s body, though I’ve found no information about DNA testing for the coat colour of this particular specimen.

Most likely occurring colours among wild horses would likely be bay, bay leopard, bay dun, black, black dun, bay dun leopard and possibly black leopard and black dun leopard, all combined with or without pangaré and likely with long manes in cold or wet areas and short manes in dry areas. It is not clear when the leopard and black genes started to occur together, since the leopard gene was originally restricted to Europe outside of Iberia, and the black colouring has developed in Iberia and only later started to spread to the Leopard area.

http: //qr.ae/TUNsJy 
Reply  ·  
Eurwentala's avatar
Thanks for your comment! I'm glad Pleistocene horses generate such interest.

I have not heard of the Yukon horse with a long mane and dun colour. The presence of a long mane in wild horses is, to my knowledge, quite controversial. Could you send me a link? I'd love to learn more. Has it been assigned to a species?

The chestnut allele is known from a single sample of Copper Age horse, which might or might not have been domesticated. This is from around the same time the first signs of domesticated horses arriving to Europe. The paper is probably already familiar to you: www.pnas.org/content/108/46/18…

On the other hand, the leopard spotting pattern in much older than Botai horses, having been found in the same study I linked above, on four Pleistocene wild horses. It's therefore quite likely that it was present in the wild horse stock well before the domestication of Przewalski horse ancestors.

The Dun gene has in fact been identified and tested on predomestic horses in 2016. It turned out there are three genotypes: D - dominant dun, the type exhibited by Przewalski horses. d1 - a "mild" non-dun with darker colouring than dun, but primitive markings still visible, which was also present in wild horses. d2 - the full non-dun genotype in most domestic horses. Source: www.nature.com/articles/ng.347…

Pangare or some equivalent seems likely to have been present in most wild horses, given how common countershading is in wild animals.

I think at the moment, with only a handful of studies on wild horse colouration, it's too early to say much about when or where each colouration originated. Especially proving a negative - saying a colouration was NOT there at some time or place - is next to impossible with the sample sizes we have. You might be right - but there's really no way to know yet, I think. If we had sample sizes of a few hundred for each time and area, then we could draw conclusions.
Reply  ·  
Eurwentala's avatar
Nevermind, found it! Thanks, this is hugely interesting.
Reply  ·  
oxpecker's avatar
oxpecker|Professional Traditional Artist
Very nice work! I recently illustrated a similar study, but I was a little more conservative and decided not to include chestnuts: European Wild Horse Colouration
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
Those are really nice, too! Is there a reason to suspect non-dun allele was present in wild horses? I, on the other hand, decided to be conservative and not include those. :D
Reply  ·  
oxpecker's avatar
oxpecker|Professional Traditional Artist
Yes, this paper by Imsland and colleagues (2016): www.ncbi.nlm.nih.gov/pmc/artic…
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
Oh wow, thanks! I had completely missed that one. I'll have to update my piece.
Reply  ·  
Libra1010's avatar
 I have to admit that seeing all these lovely equine coat patterns makes me wonder if such a diversity of colouration would have been seen in other equine species now extinct (and makes me wonder about chalicothere coats into the bargain, for some reason).
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
I have a hunch that most of the remaining megafaunal species are relict populations with reduced diversity compared to their prehistoric relatives. There's evidence of coat polymorphism in mammoths and whole extinct ecotypes of grey wolves. Living zebras still have a surprising diversity of coat morphs, and used to have a lot more before the quagga went extinct.

So... I think adding variable coat patterns to extinct animals is within the realm of plausible speculation. :)
Reply  ·  
Libra1010's avatar
 Quite so!Nod 
Reply  ·  
A-Hippocampus's avatar
Lovely! These horses are great!
Reply  ·  
Thanda's avatar
Thanda|Professional General Artist
Pretty interesting! And very usefull for paleo artist ^^ Ty!
Reply  ·  
Dontknowwhattodraw94's avatar
Dontknowwhattodraw94|Hobbyist Traditional Artist
This is very useful! 
Reply  ·  
WillemSvdMerwe's avatar
Very informative, great work!
Reply  ·  
herofan135's avatar
herofan135|Hobbyist Traditional Artist
Woah, this one is so beautiful! Great artwork!
Reply  ·  
angelahedderick's avatar
angelahedderick|Professional Traditional Artist
Beautiful and interesting - kudos on all the work that went into understanding this even before you started drawing!
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
Thanks! It did take quite a bit of reading, especially as I'm not a horse person. But it was all good fun. :)
Reply  ·  
bh1324's avatar
It's kind of sad how most of the ancestors of our domestic stock had been persecuted so much. I mean other than the wild boar and the red junglefowl, they either have gone nearly extinct or completelly extinct.
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
Agreed. Megafauna hasn't fared too well in the Holocene. :/
Reply  ·  
The red junglefowl are actually declining because they breed with chickens.
Reply  ·  
Jdailey1991's avatar
Are we absolutely sure that today's horses were selected from the tarpans?
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
My hunch is that there used to be a large and somewhat continuous range of wild horses from tarpans to Przewalski's horses, with a bunch of local populations. Today's horses are probably more or less a mix of them, but I haven't looked into it in much detail.
Reply  ·  
Spottedchest's avatar
This is such a cool and informative chart, the horses look so cute. I have a few questions though:
First, why did you decide to depict chestnut when the paper you referenced say that none of the pre-domesticated horses they tested were genetically chestnut?
Second, did you know that the amount of white on leopard spotted horses is most likely controlled by a larger number of alleles/modifiers? PATN1 leads to horses that are predominately white with spots if the horse has at least 1 copy of Lp, but the other patterns like blanket seem to be created through an additive effect of PATN genes. It's really cool, but makes predicting what a horse will look like kind of difficult XD
Here's some more info on Leopard Spotting in horses: www.appaloosaproject.co/articl…
And here's some about night blindness linked to Leopard Spotting: www.appaloosaproject.co/articl…
Reply  ·  
Eurwentala's avatar
Eurwentala|Professional
Thanks!

In the paper, they said there were no chestnut horses, but there was one horse that carried one copy of the recessive e allele. When two of those produce offspring, some of them will be chestnuts. Similarly, there was a handful of horses with one copy of the Lp allele, but none that had two copies - but I depicted a few possibilities of homozygous Lp horses as well, since those would necessarily have been born, too.

Yes, I know the leopard spotting complex is... well, complex. :D Since none of the modifiers could be tested on wild horses, I simply depicted a selection of possible patternings, both with and without PATN1. Should probably have made it clearer in the description though.
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