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Dear reader, before reading this Post, please examine the adaptive colouration in https://www.kimballstock.com/preview.asp?db=a&image=MAM+14+KH0230+01.
This specimen of the donkey (Equus asinus) exemplifies a wild-type, symmetrical colouration, free of the erratic markings that selective breeding usually produces in domestic mammals. And this, in turn, implies retention of the original colouration of a wild ancestor.
Which marking or pattern do you find most intriguing?
Now please examine this specimen (https://www.veterinary-practice.com/article/how-can-vets-alleviate-anthelmintic-resistance-in-donkeys).
A part of the body to focus on is the inner foreleg, where the chestnut (https://en.wikipedia.org/wiki/Chestnut_(horse_anatomy)) is located.
The point to note is that this surface has no striping on the pelage.
The surface in question, around the chestnut, has previously had no anatomical name. However, I will call it the intraradial surface, based on the fact that the leg bone here is the radius (https://en.wikipedia.org/wiki/Radius_(bone)).
Now, focus on this specimen: https://www.istockphoto.com/photo/wild-donkey-in-countryside-field-feeding-grazing-animals-roaming-free-new-forest-gm510494357-46947482.
There is an intriguingly crisp border to the white pelage on the intraradial surface. Furthermore, the outer surface of the foreleg, at the same height, has faint horizontal striping.
In the following mother and infant (https://naturerules1.fandom.com/wiki/Domestic_Donkey?file=01521393.jpg and http://photorator.com/photos/images/mother-donkey-and-her-foal--13135.jpg), the border in question actually takes the form of a distinct - albeit short - dark stripe, running at an angle of about 45 degrees.
Recapitulating for a moment, here is another specimen lacking any intraradial stripe: https://www.dreamstime.com/donkey-overcast-day-wild-donkey-countryside-field-feeding-grazing-animals-roaming-free-donkey-eats-grass-donkey-image183933539.
Furthermore, there is likewise no intraradial stripe in Equus somaliensis, a fully wild relative of the donkey that retains some striping on the legs in all individuals: https://www.alamy.com/stock-photo-somali-wild-ass-16293550.html.
The following shows that there may originally have been a link between the stripe on the inner foreleg and that on the outer foreleg: https://www.inaturalist.org/observations/4097145.
In the following (https://www.zmescience.com/science/world-donkeys-threatened-06052021/), the whitish has transgressed its usual border, without obliterating the diagonal stripe.
The following are further illustrations:
https://www.inaturalist.org/observations/105691878
https://www.inaturalist.org/observations/47454998
https://www.inaturalist.org/observations/93654526
https://www.inaturalist.org/observations/99519086
https://www.dreamstime.com/stock-photo-donkey-africa-walking-freely-village-botswana-image70282114
https://www.inaturalist.org/observations/58266588
https://www.dreamstime.com/donkey-farm-meadows-front-image136576486
https://www.kimballstock.com/preview.asp?db=a&image=MAM+14+KH0207+01
https://www.inaturalist.org/observations/106146800
Here is a description of the intraradial signature:
Both the ancestry and the adaptive function of the intraradial signature remain to be explained.
So, dear reader, now that you are familiar with this intraradial signature, can you figure out who is who in this view? https://www.inaturalist.org/observations/61514664
https://www.inaturalist.org/observations/60622536
Comentarios
None of the following hybrids retains an intraradial signature:
https://www.smh.com.au/environment/conservation/meet-the-zonkey-a-zebradonkey-hybrid-20131102-2wtw4.html
https://themercury.com/news/what-do-you-get-when-you-cross-a-zebra-and-a-donkey-zyla-the-zonkey/article_50e1f6d1-b46d-5e4c-a1fa-4f7455bf3f4e.html
https://www.youtube.com/watch?v=qBs5mOqpDWU
Equus grevyi has no resmblance to the donkey, in the colouration of its intraradial surface: https://www.shutterstock.com/image-photo/grevys-zebra-equus-grevyi-imperial-largest-2069467292.
https://novum-terram.fandom.com/wiki/Nubian_wild_ass_(SciiFii)?file=Nubian_wild_ass_%2528SciiFii%2529.jpg
Individual with maximal expression of striping, extending to the back:
https://i.pinimg.com/originals/11/0a/9f/110a9f83e1e80debaa9ea26a54c361e2.jpg
@botswanabugs About what percentage of individuals of the donkey in your area have the wild-type colouration? And what percentage possess the intraradial signature?
Thanks for this enlightening article @milewski , I shall certainly now take photos of the domestic donkeys of central Botswana !
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