Prediction that Saiga will be found to have ultraviolet-reflecting panel on side of body

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Dear readers, first please see:

RUMINANT:
https://www.texashunterproducts.com/blog/scientific-facts-about-how-deer-see-and-hear/
https://www.youtube.com/watch?v=cvH4NcUt1RA
https://bowhunting.net/2019/02/confirmed-deer-see-ultraviolet-what-does-this-mean-to-hunters/
https://www.themeateater.com/wired-to-hunt/whitetail-hunting/deer-vision-how-whitetails-see-color-light-and-movement
HUMAN:
https://petapixel.com/2012/04/17/the-human-eye-can-see-in-ultraviolet-when-the-lens-is-removed/
https://wonderopolis.org/wonder/Why-Can%E2%80%99t-We-See-Ultraviolet-Light
https://www.bbc.com/future/article/20150727-what-are-the-limits-of-human-vision
https://www.newscientist.com/lastword/mg24432591-000-super-seers-why-some-people-can-see-ultraviolet-light/

The important point is that ruminants, as exemplified by Odocoileus, can see ultraviolet light, whereas the human species can do so only poorly. This is mainly because the human eye has an ultraviolet filter in the lens, whereas ruminants, and probably other ungulates plus Carnivora,

• lack any such filter, and
• have particular sensitivity in the whole blue-violet-ultraviolet range.

With this background information in place, let us proceed to the particular topic of this Post.

Various spp. of ungulates, adapted to living gregariously in open environments, tend to have conspicuous colouration (e.g. see lhttps://www.inaturalist.org/journal/milewski/66546-a-hyperconspicuous-horse-hiding-in-plain-sight#).

In this syndrome, both sexes and, in some cases, even infants are rendered conspicuous, by virtue of pale, dark, or combinations of pale and dark.

These patterns make the whole bodies stand out from treeless backgrounds by day, and even to some degree by night.

In environments where there is great visibility, and no chance for adults to hide, self-advertisement at the whole-body scale would seem to make adaptive sense.

An exception to this trend seems to be the genus Saiga (https://www.inaturalist.org/taxa/42378-Saiga-tatarica), which is extremely adapted to gregariousness in open environments in Eurasia, yet has plain colouration. This colouration seems to conform to crypsis (https://en.wikipedia.org/wiki/Crypsis).

In this Post, I predict that Saiga will be found to possess an ultraviolet-reflecting panel on the side of the body, conspicuous in the eyes of the relevant ungulates and carnivores.

I.e. I predict that the plainness of Saiga reflects the limitations of the human visual system, rather than the real colouration of this bovid.

This hypothesis should be technically testable, initially using study skins in museums.

First, let us examine some details of the relatively plain colouration of Saiga.

Saiga is unique in several ways. It is the approximate Eurasian ecological counterpart of the gazelle genus Antidorcas (https://www.inaturalist.org/taxa/42283-Antidorcas-marsupialis) of southern Africa, and the antilocaprid genus Antilocapra (https://www.inaturalist.org/taxa/42429-Antilocapra-americana) of North America.

However, it is unlike these genera in having considerably different colouration in summer vs winter.

The summer coat is more plain than the winter coat.

In the winter coat there is a noticeable pattern, consisting of whitish fur on the posterior haunches, and a dark midline on the rump.

The following (https://s-media-cache-ak0.pinimg.com/originals/70/26/be/7026be736eb8202ba8a1e1cdd056f3c7.jpg)
shows the modest pattern of dark/pale contrast present on the rump of Saiga, in winter coat.

During the rutting season in mid-winter, mature males acquire conspicuous darkness on the cheeks, forelegs, chest, and particularly the ventral half of the neck (https://mobile.twitter.com/SaigaCA/status/1491426672553312259/photo/1 and https://www.saigaresourcecentre.com/sites/default/files/2021-01/news_saiga-en_26_fin.pdf and https://onlinelibrary.wiley.com/doi/10.1111/j.1469-7580.2007.00818.x and https://www.saigaresourcecentre.com/picture/two-winter-saiga-males and https://www.saigaresourcecentre.com/picture/winter-saiga-male-right).

However, Saiga remains aberrant - at least to the human eye - relative to Antidorcas and Antilocapra, because

• the only pattern conspicuous at a distance is restricted to rutting males, and
• all patterns of colouration in females, in all seasons, are so poorly-developed that they would hardly warrant mention in other gregarious spp. of ungulates adapted to open environments.

Even within the Eurasian ‘steppes’, the other gregarious ungulates (gazelles and asses, as well as yak and camel) all have colouration more conspicuous than that of Saiga.

Saiga is never pale enough, to the human eye, to stand out from its surroundings, in the way of certain other mainly pale ruminants, such as Oryx leucoryx (https://wildlife.org/wild-cam-managing-arabian-oryx/ and https://www.thenationalnews.com/uae/oryx-must-be-saved-by-setting-up-wildlife-reserve-1.393069 and https://thelevantnews.com/en/article/saudi-arabia-welcomes-birth-of-first-arabian-oryx-in-kingdom-in-90-yearsjune-9,-2022,-7:56-am).
 
The following (https://en.wikipedia.org/wiki/Saiga_antelope#/media/File:Saiga_antelope_at_the_Stepnoi_Sanctuary.jpg) shows Saiga in summer coat.

Although there are slightly noticeable patterns of pale near the tail-root and near the elbow, there is nothing that deserves to be called a bleeze.

This lack of whole-body conspicuous colouration in Saiga leads me to suspect that the human eye is incapable of perceiving a relevant pattern. 

When one looks closely at the pelage on the flanks of the summer coat of Saiga, one notices a difference in texture: https://www.theguardian.com/science/animal-magic/2015/jun/12/134000-saiga-antelope-dead-in-two-weeks-what-is-the-probable-cause.

There is a panel, not much different in its fawn colouration, that has a different quality of fur, in more or less the same position on the lower flanks as is toned conspicuously dark in gazelles, or conspicuously white in Antilocapra.
 
The following view of the summer coat (http://images.earthtouchnews.com/media/1947956/saiga_2017_02_01.jpg?mode=crop&width=710&height=474) once again shows that the lower flanks have a subtle paler-fawn ‘band’ between the main fawn of the dorsal surface and the countershaded whitish of the ventral surface.

To the human eye, this band is hardly noticeable. However, it would be noticeable to  the eyes of other large mammals, including Saiga itself, if it reflects ultraviolet light. I suspect that something similar applies to the haunch and sides of the neck of Saiga.
 
The following (https://structurefunctionadaptation.wordpress.com/2014/02/05/one-of-the-worlds-most-endangered-species-the-saiga-antelope/comment-page-1/) is another view of the panel on the lower flanks of the summer coat of Saiga, which I hypothesise to have a hair texture, or microsurface design on each hair, that particularly reflects ultraviolet.

What such reflection of ultraviolet would mean:
In the eyes of its own species or Canis lupus, Saiga would be effectively flank-banded in much the same way as we see in Antilocapra (https://www.snopes.com/fact-check/pronghorn-antelope-saturn/).

I hypothesise that humans get a misleading view of Saiga, owing to the fact that our lens filters out most of the ultraviolet light - which does not happen in most ungulates or cursorial Carnivora.
 
The following (http://www.edgeofexistence.org/edgeblog/wp-content/uploads/2008/09/Sept-08_Female-Mongolian-sa.jpg) once again shows the summer coat, illustrating the subtle difference in pelage texture between upper flank and lower flank (as well as neck and haunches).

However, I predict that if this scene were to be filmed by means of an instrument that registers ultraviolet light, the lower flanks of Saiga would appear gleamingly pale, possibly even when the surface in question is shaded.

This would be evolutionarily convergent with Antilocapra, in which the white bleeze on the lower flank is owing to a lack of pigmentation, combined with a microstructure of the hairs that enhances reflection of all of the wavelengths visible to the human eye.

Any evolutionary convergence with Antidorcas and other gazelles is more complicated, because their conspicuousness on the lower flanks is partly owing to dark pigmentation (https://en.wikipedia.org/wiki/Springbok#/media/File:Antidorcas_marsupialis).

In summary:

In Antidorcas and several other spp. of gazelles, whole-body conspicuousness is conferred mainly by intense pigmentation, juxtaposed with a complete lack of pigmentation, forming a dark/pale band on the lower flank. Both the dark and the pale are fully visible to the human eye.

In Antilocapra, whole-body conspicuousness is conferred partly by a lack of pigmentation on the lower flank, possibly enhanced by microstructure of the hairs. The pale is visible to the human eye, although some enhancement by reflection of ultraviolet - in the eyes of ungulates and carnivores - cannot be ruled out.

In Saiga, I hypothesise that paleness - virtually invisible to the human eye - on the lower flanks is conferred by a peculiar microstructure of the hairs, that particularly reflects ultraviolet.

Posted on August 24, 2022 02:15 AM by milewski