Caleonic colouration in the caribou, part 1

(writing in progress)

A well-recognised form of conspicuous colouration in medium-size to large animals is the pied pattern (https://www.tripadvisor.com/LocationPhotoDirectLink-g469397-d469470-i381557535-Bontebok_National_Park-Swellendam_Overberg_District_Western_Cape.html and https://www.flickr.com/photos/myplanetexperience/50867088327). This consists of a dark/pale patchwork too bold to function disruptively, i.e. for camouflage.

However, another conspicuous pattern, less familiar but obvious in certain mammals, deserves a name. I provisionally call this 'caleonic colouration'.

Caleonic colouration has arisen repeatedly in lineages as diverse as

It is normal for the ventral parts of the body to be pale, as part of the inconspicuous pattern called cryptic colouration (https://en.wikipedia.org/wiki/Countershading). However, the extension of this pale switches the effect to conspicuousness. This is because the pale, encroaching upwards towards the dorsal side, tends to catch the sunlight at all seasons and most times of day.

This ‘lateralisation’ of the pale parts of the pelage occurs variously on the cheeks, neck, shoulders, flanks, and/or hindquarters. In extreme cases it reaches the dorsal surfaces of the rump, the neck, and even the back. This achieves whole-body conspicuousness for gregarious species living in the open, where it is hard to hide anyway.

In the caleonic pattern, the figure is 'highlit' by what seems to be a flame located below it.

In a sense, animals with caleonic colouration have ‘inverted’ the principle of countershading, to achieve whole-body conspicuousness instead of crypsis (https://en.wikipedia.org/wiki/Crypsis). This differs from the pied pattern, in which countershading is redundant owing to the large-scale dark/pale contrast in the pigmentation of the pelage.

In this series of Posts, I show that the widespread species Rangifer tarandus (https://www.inaturalist.org/taxa/42199-Rangifer-tarandus) has certain subspecies with pied colouration, and others with caleonic colouration. This arguably makes it the only species of mammal in which both patterns occur, depending on the location.

(Besides R. tarandus, the only species which I know to possess caleonic colouration in only certain populations is the domestic horse Equus caballus. However, this is qualified by the likelihood that the domestic horse has arisen by hybridisation among several wild congeners during the process of selective breeding.)

Please bear in mind that R tarandus undergoes seasonal moult of the pelage, in which the pigmentation wears out during the winter, and the re-growing fur initially looks fairly uniform in of spring/early summer, before the hairs acquire their full effect. Thus the fully-differentiated colouration tends to be expressed in autumn, corresponding to the rutting season.

The following shows pied colouration in Rangifer tarandus: https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057000.html?imageid=CA708987-0B78-4D58-A301-7570ACD15211&p=365985&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-with-female-calf-on-migration-south-41499424.html?imageid=24FDBEC7-2515-4910-A5C6-57A0352BEF7C&p=54193&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-female-in-snow-on-migration-south-through-41499304.html?imageid=013FADBA-BE26-48E8-96CC-B83A1BEDFC74&p=54193&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057056.html?imageid=8BFBDFF1-5FE8-4504-BC54-0C1ED673978D&p=365985&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/caribou_trails/caribou_trails_2014.pdf.

The following shows caleonic colouration in Rangifer tarandus: https://www.inaturalist.org/observations/28836472 and https://www.natureinstock.com/search/preview/woodland-caribou-rangifer-tarandus-caribou-bull-in-town-newfoundland-canada/0_10121446.html and https://www.mindenpictures.com/stock-photo-woodland-caribou-rangifer-tarandus-caribou-male-newfoundland-canada-naturephotography-image00596574.html and https://m.facebook.com/NewfoundlandLabradorTourism/photos/a.111088443781/111092763781/?type=3 and https://www.inaturalist.org/observations/9039103 and https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/38196369.

Pied colouration occurs in the autumn coat of most of the subspecies of Rangifer tarandus, including R. t. groenlandicus and R. t. granti. The darkest parts are muzzle, forelegs, brisket, and lower flanks, while the palest are nose (rhinarium), neck, beard/dewlap, tail and the narrow rump-blaze. These features are arranged to provide dark/pale contrast, not crypsis or disruption of the outline of the animal.

Caleonic colouration occurs in the subspecies found on two systems of islands, far apart geographically. On the Arctic islands occurs subspecies, R. t. pearyi (https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/mammals/peary-caribou.html and https://www.inaturalist.org/guide_taxa/1119027 and https://www.alamy.com/stock-photo-bull-caribou-in-velvet-antlers-stands-in-the-colorful-autumn-tundra-75290355.html?imageid=89F3DD5C-43FB-48AC-B540-F92A8006B30D&p=228679&pn=25&searchId=9892403e79eeaa448727cb13a1e36c01&searchtype=0). On the island of Newfoundland (https://en.wikipedia.org/wiki/Newfoundland_(island)) occurs subspecies, R. t. terranovae (https://www.naturepl.com/stock-photo-woodland-caribou-nature-image00596572.html and https://www.shutterstock.com/de/image-photo/caribou-adult-female-rangifer-tarandus-avalon-1911012163).

I agree with Valerius Geist that R. tarandus on the island of Newfoundland is quite distinct from other forms of ‘woodland caribou’, and that taxonomy took a wrong turn when R. t. terranovae was lumped with R. t. caribou.

The following illustrate R. t. terranovae: https://mobile.twitter.com/NFLDdesigns/status/1339255210749865986/photo/1 and http://www.nlnature.com/Newfoundland-Canada-Nature/1520.aspx and http://birdingnewfoundland.blogspot.com/2009/12/southern-avalon-peninsula-birds-and.html and second photo in https://www.cbc.ca/news/canada/newfoundland-labrador/reindeer-deer-lake-video-1.4918560.

In the pied pattern, the lower flanks, chest, lower shoulders, and brisket are the darkest parts of the animal. This differs from the caleonic pattern in R. t. terranovae, in which all these parts are the palest parts of the animal. It is hard to see how the two patterns of colouration in R. tarandus, namely pied and caleonic, can be represented as extremes on a continuum. Instead, what seems to have happened is that in an ancestral form the whitish at the belly has spread so far up that it has replaced the entire flank-band complex in the pied pattern, while at the same time the legs have gone from basically dark to basically pale, and the neck has acquired a darkish dorsal zone in the caleonic pattern.

In Rangifer tarandus terranovae, I find at least three aspects detracting from any simple characterisation of the pattern as caleonic:

  • some individuals do retain a faint version of the flank-banding typical of most subspecies of R. tarandus,
  • the pale of the neck tends to be disjunct from the pale of the shoulders and flanks, separated by a more-or-less vertical tract of pale greyish-fawn fur, and
  • the pale of the lower haunch tends to give way to a darker tone on the upper leg in some individuals.

What this means is that the pattern of colouration in R. t. terranovae is not categorically different from that in other subspecies. However, the combination of a caleonic tendency (particularly on flank and haunch) and an overall pallour set this subspecies apart from all other subspecies besides R. t. pearyi. Whereas ‘woodland caribou’ in the western part of the boreal zone of North America are unusually dark for the species (e.g. according to Valerius Geist), R. t. terranovae is unusually pale, particularly considering that it lives at a far lower latitude than pearyi.
  
Please see e.g. https://www.wildandexposed.com/journal/2018/10/17/marks-adventures-in-newfoundland
 
I take the following to be in July or August. Last year’s guard pelage is still moulting.
 
The following, probably in July, shows the extreme pattern of colouration, so different from that of other R. tarandus (except for pearyi). The diagonal border between darker and paler on the haunch is diagnostic of terranovae, and does not occur in the other subspecies of R. tarandus including pearyi. This photo shows the fresh underpelage of summer; the guard pelage has yet to appear. Note that the face is the darkest part of the animal (with one patch of last year’s guard pelage still to fall out completely). Note that the whitish extends above the knee, which is consistent with caleonic colouration.

The following is of the mature male, probably in August-September, with the guard pelage emerging on the neck. The diagonal tonal contrast on haunch is diagnostic of R. t. terranovae.

The following is similar seasonally to that above, but the face not as dark, and the knee region not included in the pale tract.

I take the following to be the mature male in September, in something approaching the pattern of colouration of the autumn. There is no trace of the flank-banding typical of most subspecies of R. tarandus.
 
http://conservationbiologynewfoundland.blogspot.com/2012/04/newfoundlands-wilderness-reserves.html

I take the following to be in August, with the new underpelage complete. In this case the pale diagonal on the haunch gives way to darker on the upper hind leg.

The following two male individuals, probably in September, show some features linking the ‘typical’ pattern above to the pattern typical of other subspecies of R. tarandus. These include the relative darkness of the legs and the faint banding on the flank. These detractions notwithstanding, this colouration remains different from those of any other forms of ‘woodland caribou’ at the same season.
 
https://www.alamy.com/stock-photo-two-caribou-rangifer-tarandus-forage-during-autumn-in-gros-morne-national-43870484.html

I take the following to be in September, just before the rutting season. This individual has a pattern on its flank which is a faint version of that in most other subspecies of R. tarandus. However, the difference remains that the colouration is pallid instead of pied.

The right-hand photo below shows what I take to be the mature male in autumn, during the rutting season. Note the separation of the pale of the neck from the pale of the elbow region.

I take the following to be the adolescent male in autumn. The side of the body shows a faint version of the banding seen in most subspecies of R. tarandus. The face is not dark here as it is in several of the males above which I assume to be because the guard pelage has emerged on the face.
 
http://www.hww.ca/en/wildlife/mammals/caribou.html

If the following is in autumn, it illustrates the point that in terranovae there is no pied pattern of colouration.

Because both sexes are in hard antler together, I take the following two photos to be in autumn, near or in the rutting season. In the first of these two photos, two of the female individuals plus the juvenile retain, albeit in pallid form, the flank-banding typical of other sspp. of R. tarandus, which detracts from the caleonic pattern.
 
The mature males in the following show the typical colouration of terranovae.

I take the following two photos to be in September, with the colouration approaching that of the rutting season.

I take the following to be in the rutting season. This colouration is different from the pied colouration of R. t. groenlandicus and R. to granti in the rutting season.

I have pointed out, above, that some individuals of R. t. terranovae have a faint version of the flank-banding seen in other subspecies of R. tarandus, and that this detracts from/tends to compromise the caleonic pattern. However, this may perhaps be owing to some degree of anthropogenic mixing with another subspecies.
  
Wilkerson (2010, https://www.mun.ca/biology/scarr/Wilkerson%202010,%20excerpt.pdf) states that the domestic reindeer (R. t. tarandus) was introduced to the island of Newfoundland early in the twentieth century, and that there was indeed contact between this subspecies (which possesses flank-banding) and the indigenous populations, viz R. t. terranovae

My hypothesis is therefore that the original appearance of the Newfoundland form was truly caleonic to the exclusion of the flank-banding.

(writing in progress)

Posted by milewski milewski, June 22, 2022 21:31

Comments

CARIBOU IN LABRADOR IS NOT CALEONIC

Rangifer tarandus occurs in Labrador, which is on the mainland near Newfoundland. This form is nominally referred to R. t. caribou, but this subspecific name may not mean much in this far-east location.
 
Here I show that the caleonic pattern of colouration, found on the islands of Newfoundland, does not occur in mainland Labrador.

The colouration in the George River population of mainland Labrador is similar to R. tarandus in general, and different from e.g. the Avalon Peninsula of the island of Newfoundland as seen in https://www.youtube.com/watch?v=sYcdIw2si-U.

The following show the appearance of R. tarandus in the George River population of mainland Labrador.

https://www.gettyimages.com.au/detail/photo/caribou-of-the-george-river-herd-canada-high-res-stock-photography/585852764
 
https://www.thetelegram.com/opinion/local-perspectives/editorial-caribou-crisis-136292/

https://www.newfoundlandbiggamehunting.com/post/asleep-at-the-wheel-while-390-000-caribou-of-the-george-river-caribou-herd-vanishes
 
http://www.firstnationsdrum.com/2018/12/all-harvesting-of-george-river-caribou-should-cease-says-minister/
 
https://montrealgazette.com/news/local-news/inuit-first-nations-sign-historic-pact-to-protect-quebec-caribou

https://i2.wp.com/huntforever.org/wp-content/uploads/2016/08/precious-memories-caribou-herd-090216.jpg?ssl=1

https://i1.wp.com/huntforever.org/wp-content/uploads/2014/12/mountaincaribou2.jpg?ssl=1

https://i1.wp.com/huntforever.org/wp-content/uploads/2013/06/caribou-060713.jpg?ssl=1

https://www.newfoundlandbiggamehunting.com/posts

http://www.newfoundlandoutdoors.net/caribouhunting.html

These findings suggest that the colouration of R. t. terranovae, which I take to be restricted to Newfoundland sensu stricto, is distinctive from that on the nearby mainland, in being caleonic.

Posted by milewski about 2 months ago (Flag)

Evolutionary convergence in conspicuous colouration between Arctic fox and Tibetan wild ass:

The Arctic fox (Alopex lagopus) and Tibetan wild ass live allopatrically, but both in a sense inhabit ‘tundra’. Their patterns of colouration are remarkably similar, considering that one is much smaller-bodied than the other, and a carnivore instead of a herbivore.

In both cases, the pale of the ventral surfaces has extended so high on the sides of the animal that the whole effect is flag-like, i.e. the colouration is conspicuous. The pale has particularly crept up on the hindquarters (between haunch and tail), on the area just posterior to the shoulders, and on the neck (but not the face).

The main difference, apart from the far bushier tail of the fox, seems to be that the Arctic fox retains dark legs/feet, whereas the Tibetan wild ass has pale legs/feet.

http://imgc.allpostersimages.com/images/P-473-488-90/38/3814/V5QIF00Z/posters/tom-walker-male-arctic-fox-in-summer-coloration-on-the-arctic-tundra-alopex-lagopus-alaska-usa.jpg

http://www.skolaiimages.com/stock/albums/alaska/anwr/pbay_arcticfox_002.jpg

http://4.bp.blogspot.com/-QlhXs1WZmro/Tpp0Mxgsa5I/AAAAAAAABUE/fSNLJoxBn6E/s1600/D2H_1524.jpg

http://static.zoonar.com/img/www_repository2/54/38/f4/10_9acc6df8ce0dac743bc0f3cb1d99ab03.jpg

The Arctic fox is coloured for inconspicuousness in winter (all-white) but conspicuousness in summer. Why would the Arctic fox want to be conspicuous in summer but inconspicuous in winter?
 
In the case of Arctic/boreal mustelids, the situation may also be more complex than it seems. Several weasel-like species turn white in winter but their summer coats are hard to interpret because they, a bit like the Arctic fox, have conspicuous aspects (e.g. even the winter white coats have dark tail-tips). In the case of the wolverine, the main pattern is a perverse one in which the animal remains dark, so dark that it stands out from a snowy background in what I interpret to be a form of aposematism (which incidentally it shares with the musk-ox in a way).
 
Stoat (Mustela erminea):
When the white (winter-coat) stoat is in a non-snowy situation, the whole animal stands out in a way consistent with aposematism rather than crypsis; and that the dark distal part of the tail would be unmistakeably conspicuous even against an all-snow background. In the summer coat, the animal stands out like a beacon when it adopts a bipedal stance. This, exposing what could be assumed to be a merely countershaded ventral surface but is too abruptly demarcated to conform to that model even when the animal slinks along quadrupedally. 

http://en.wikipedia.org/wiki/Stoat#mediaviewer/File:Mustela_erminea_winter_cropped.jpg

http://en.wikipedia.org/wiki/Stoat#mediaviewer/File:Mustela_erminea_upright.jpg

Posted by milewski about 1 month ago (Flag)

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