Who has spotted an intraradial signature in the domestic donkey?

@tonyrebelo @capracornelius @beartracker @matthewinabinett @biohexx1 @lonnyholmes @chewitt1 @oviscanadensis_connerties @paradoxornithidae @jeremygilmore @ludwig_muller @grinnin @jacqueline_llerena

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.dreamstime.com/photograph-dark-brown-tan-donkey-walking-his-pasture-dark-brown-donkey-walking-pasture-image196350035

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.dreamstime.com/mini-donkey-walking-field-close-up-spring-summer-day-sunshine-shows-close-up-side-view-mini-donkey-farm-image218364413

http://l7.alamy.com/zooms/174c2356d3284f859135f28c0f221bc7/france-provence-female-donkey-feeding-milk-to-new-born-foal-on-meadow-d7k5ke.jpg

https://www.inaturalist.org/observations/106146800
 
Here is a description of the intraradial signature:

• The whitish of the brisket area extends ventrally on the inner surface of the upper fore leg, to surround the chestnut, which is bare skin.
• The chestnut in the donkey is moderate in size relative to other members of the genus Equus, but usually dark enough to be visible.
• The border between the whitish pelage and the greyish ground-colour of the rest of the upper fore leg is, in some individuals, emphasised by dark pigmentation.
• There is often a faint dark stripe on the outer surface of the same fore leg, at about the same height above ground.
• There is also a somewhat dark vertical streak extending ventrally from the chestnut towards the carpal joint (I do not know if this results from pigmentation of the pelage or some sort of discolouration discharged by the chestnut).
• This dark/pale/medium tone configuration of small-scale features constitutes a kind of individually variable signature.
• The intraradial signature is absent - except for the chestnut - from some individuals, even within the 'wild-type' colouration.

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

Posted on September 3, 2022 02:09 AM by milewski