How did the donkey get a frontal bleeze?

One of the most conspicuous features of the adaptive colouration of wild ungulates is the frontal bleeze (e.g. Damaliscus pygargus phillipsi https://www.zoochat.com/community/media/blesbok-damaliscus-pygargus-phillipsi.487604/).

This is a pale/dark feature so obvious that it divulges the presence of the ungulate to scanning predators, even at a distance and even if the figures remain stationary (https://www.alamy.com/stock-photo-herd-of-blesbok-in-field-africa-87078020.html).

As discussed in previous Posts, bleezes have evolved presumably because, in the life history strategy of certain gregarious species of open environments, it is more important to remain easily monitored by companions than it is to hide from predators.

Bold markings occur also in domestic ungulates, but usually not in the form of bleezes. They function differently, being a mainly inadvertent result of selective breeding. Humans can protect their livestock from predators, so natural selection for wild-type colouration is relaxed. Furthermore, it suits herders to be able to spot strays easily; and piebald, individualised markings are regarded as aesthetically pleasing by pastoral cultures.

The distinction between wild-type and domestic colouration, in these conspicuously pale or dark patches, is a matter of bilateral symmetry and individual consistency. Markings produced by domestication tend to be erratic (e.g. https://longmeadowrescueranch.org/barnbuddies/geppetto-2/).

However, there is an apparent exception in the case of the donkey (Equus asinus). In certain large-bodied Iberian breeds such as the Balearic (https://en.wikipedia.org/wiki/Balearic_donkey) and the Catalan (https://en.wikipedia.org/wiki/Catalan_donkey), a frontal bleeze has arisen in domestication from ancestors which, as far as we know, lacked any bleeze.

How and why has wild-type colouration come to be 'reinvented' anthropogenically in this case?

The novel bleeze seen in Iberian breeds of the donkey consists of a strikingly pale muzzle on an otherwise dark face (https://fineartamerica.com/featured/wild-burro-nevada-jan-lewis.html and https://www.inaturalist.org/observations/48410657 and https://www.inaturalist.org/observations/45581467 and https://www.dreamstime.com/stock-photo-wild-black-donkey-pasture-burro-standing-looking-ahead-alert-expression-full-body-side-view-image58393196).

In this configuration, it is the dark aspect that is different from the wild ancestors. All species of wild asses have pale on the muzzle, but this is hardly conspicuous because the rest of the face is usually medium in tone:

Equus kiang
https://stock.adobe.com/bg/search?k=onager&asset_id=296475961 and https://www.projectnoah.org/spottings/394553031 and https://www.istockphoto.com/photo/wild-ass-kiang-gm157747840-22292105 and https://www.istockphoto.com/photo/kiang-gm462912429-32514774 and https://www.researchgate.net/figure/An-adult-male-Equus-kiang-subspecies-kiang-in-summer-coat-from-eastern-Ladakh-India_fig1_262137189

Equus hemionus onager
https://stock.adobe.com/bg/search?k=onager&asset_id=61074577 and https://stock.adobe.com/bg/search?k=onager&asset_id=112934812

Equus hemionus kulan
https://stock.adobe.com/bg/search?k=onager&asset_id=291249306

Equus hemionus khur
https://hive.natureinfocus.in/photo_sharing/indian-wild-ass-2

Equus africanus somaliensis
https://focusedcollection.com/165616364/stock-photo-somali-wild-ass.html and https://pixabay.com/photos/somali-wild-ass-desert-negev-israel-4764744/

Because the dark on the face is merely part of an overall darkness in the breeds in question, the puzzle resolves to: why did selective breeding of the donkey in Spain favour dark overall colouration instead of the irregular patchwork typical of domestic livestock?

In order to answer this, it is first necessary to consider the importance of the donkey in the breeding of mules (see https://www.mulemuseum.org/history-of-the-mule.html and https://en.wikipedia.org/wiki/Mule).

A poorly-appreciated aspect of the donkey is that it is unique among domestic animals in having been selectively bred mainly for the purposes of producing an interspecific hybrid.

Of course, it is true that the donkey, in the form of small-bodied breeds, has been economical for poor people in many countries since ancient times. However, production of mules (hybrids produced by males of the donkey and females of the horse, e.g. https://luckythreeranch.com/site/wp-content/uploads/Draft-Mule.jpg) has for an equally long time been where real profits lay, to the benefit of politically powerful - and often belligerent - elites.

Thus it has been the production of not the working breeds of the donkey but rather suitable sires for large, strong, sombre-looking mules that has long been the main incentive behind selective breeding of the donkey (see https://www.defensemedianetwork.com/stories/the-virtues-of-stubbornness-mules-at-war/). This means a particular demand for breeds of the donkey which combine an imposing body size (average adult male body mass preferably exceeding 400 kg, e.g. https://fuives.com/en/ and https://luckythreeranch.com/site/wp-content/uploads/Mammoth-Donkey.jpg) and the sort of colouration that means business.

Is it mere coincidence that the front-of-ear pattern - which risks giving the donkey a comical appearance - has been muted in the Catalan breed? (https://www.istockphoto.com/photo/huge-furry-catalan-donkey-pasturing-gm1153043674-313029467 and https://stock.adobe.com/search?k=%22catalan+donkey%22&asset_id=81299484)

By the late eighteenth century it was mainly Spain and southern France which prevailed in the market for males of the donkey for the purposes of equine hybridisation (see https://en.wikipedia.org/wiki/List_of_Iberian_donkey_breeds). And it was - according to my hypothesis - in this context that a specialised colouration was chosen for the Catalan breed in particular (https://www.alamy.com/catalan-donkey-equus-asinus-f-asinus-image9523565.html).

If my interpretation is correct, the frontal bleeze in the donkey is to all intents and purposes redundant in adaptive terms. It is merely the inadvertent result of the phenotypic persistence of the paleness on the muzzle (which has passed under the radar of selective breeding because it hardly detracts from the looks of mules) combined with the otherwise relatively uniform darkness of breeds selected to look as credible as possible for the siring of large, dark, capable-looking mules serving powerful political agenda.

In other words: the Iberian breeds can be thought of as wearing what is not so much a lookalike-colouration for wild ungulates, but more an asinine equivalent of a 'business suit'.

Publicado el 23 de septiembre de 2021 a las 01:17 AM por milewski