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

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 (

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.

However, there is an apparent exception in the case of the donkey (Equus asinus). In certain large-bodied Iberian breeds such as the Balearic ( and the Catalan (, 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 ( and and and

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 and and and and

Equus hemionus onager and

Equus hemionus kulan

Equus hemionus khur

Equus africanus somaliensis and

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 and

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. 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 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. and 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? ( and

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 And it was - according to my hypothesis - in this context that a specialised colouration was chosen for the Catalan breed in particular (

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'.

Anotado por milewski milewski, 23 de septiembre de 2021 a las 01:17 AM


The following shows the relative body sizes of two breeds of the donkey, the larger one being mislabelled as a mule: The following shows the real appearance of a typical mule:

Anotado por milewski hace 25 días (Advertencia)

interesting indeed!

Anotado por devbagdi hace 25 días (Advertencia)

@devbagdi Many thanks, but you were so quick to read this that you commented even before I had finished writing :-)

Anotado por milewski hace 25 días (Advertencia)

Oh I thought it was complete and left as a question XD
I'll read it now!

Anotado por devbagdi hace 25 días (Advertencia)

Añade un comentario

Entra o Regístrate para añadir comentarios