Subtle and multifaceted adaptive colouration in the largest wild ruminant in South America: the guanaco (Lama guanicoe), part 1

(For my account of the vicuna, please see https://www.inaturalist.org/journal/milewski/74636-adaptive-colouration-in-the-vicuna-camelidae-vicugna-vicugna#)

The colouration in the guanaco (Lama guanicoe, https://ielc.libguides.com/sdzg/factsheets/guanaco/characteristics) is simple in the sense that it does not vary with sex or age. Males, females, juveniles, and infants all share the same colouration.

However, the patterns are difficult to describe, because

• the species is neither plain-coloured nor conspicuously patterned in an unambivalent and consistent way,
• subspecies remain poorly-defined, and
• there is considerable variation among individuals and populations, beyond a recognisable north-south cline.

Conspicuous features of adaptive colouration, in mammals including the guanaco, may be noticeably dark, noticeably pale, or both together in the form of dark/pale contrast.

POSSIBLE LATERAL BLEEZE:

The following is a reminder of the degree of conspicuousness of a lateral bleeze: Eudorcas thomsoni https://eol.org/pages/129521

In the guanaco, the pale of the ventral surface of the torso extends too high on the flanks to function merely as countershading.

This is true particularly for the posterior flank, on which the depigmented tract almost reaches the back/rump (https://www.inaturalist.org/observations/9193898 and https://www.inaturalist.org/observations/12747531 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-coast-patagonia-argentina-10889650 and https://www.shutterstock.com/it/image-photo/guanaco-torres-del-paine-national-park-1489331 and https://www.shutterstock.com/it/image-photo/guanaco-patagonia-argentina-145863224 and https://www.inaturalist.org/observations/49363889).

An advantage of the placement of the pale tract on the posterior flank is that the feature is conspicuous not only in profile but also in

• anteriolateral view (https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-luro-park-la-2015195615), and
• posteriolateral view (https://www.shutterstock.com/it/image-photo/patagonian-guanacos-447788968 and https://www.shutterstock.com/it/image-photo/chilean-guanacos-patagonian-lamas-grass-close-12805579 and https://www.shutterstock.com/it/image-photo/guanaco-mother-baby-peninsula-valdespatagonia-argentina-1941994570 and https://www.shutterstock.com/it/image-photo/nature-guanaco-patagonia-chile-240182590).

The following photo might not have been worth taking, were it not for the postulated lateral bleeze (https://www.inaturalist.org/observations/1241095).

The following shows the maximal extent of pale on the flanks of the guanaco: https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-patagonia-61999597.

However, for the species overall, the feature in question does not necessarily qualify as a bleeze.

This is because some populations, particularly in Peru/northern Chile and northwestern Argentina, tend to lack the pale tract (https://www.inaturalist.org/observations/62432736 and https://www.inaturalist.org/observations/68274775 and https://www.inaturalist.org/observations/101287743 and https://www.inaturalist.org/observations/120576915 and https://www.inaturalist.org/observations/130734244 and https://www.inaturalist.org/observations/141054878 and https://www.inaturalist.org/observations/119045255 and https://www.shutterstock.com/it/image-photo/guanacos-roaming-beneath-vertical-sandstone-walls-1966448038 and https://www.inaturalist.org/observations/49720955 and https://www.inaturalist.org/observations/30950180 and https://www.inaturalist.org/observations/9589818).

POSSIBLE FACIAL/LARYNGEAL/AURICULAR FLAG:

The following is a reminder of the degree conspicuousness of a facial bleeze: Damaliscus pygargus phillipsi https://777ranch.com/product/blesbok-or-blesbuck/.

A facial flag is less conspicuous than the above, but becomes conspicuousness when moved.

(For a description of laryngeal and auricular flags, please see https://www.inaturalist.org/journal/milewski/48447-conspicuous-features-of-colouration-in-giraffes#.)

The head of the guanaco tends to have dark aspects and pale aspects, in some cases in combination.

The face of the guanaco, unlike that of the vicuna (Vicugna vicugna), tends to be somewhat dark (https://www.shutterstock.com/it/image-photo/wild-guanaco-chilean-andies-1599385441 and https://www.shutterstock.com/it/image-photo/patagonia-wildlife-guanaco-chile-torres-del-2195348847 and https://www.shutterstock.com/it/image-photo/guanaco-lamas-national-park-torres-del-1012256998 and https://www.shutterstock.com/it/image-photo/family-guanacos-lama-guanicoe-desert-chile-2119401701 and https://www.inaturalist.org/observations/27661333).

Furthermore, there tends to be a pale, possibly sheeny streak from the crook of the throat to, and including, the ear pinnae (https://www.inaturalist.org/observations/7538582 and https://www.shutterstock.com/it/image-photo/guanacos-lama-guanicoe-female-cub-torres-1468689881 and https://www.shutterstock.com/it/image-photo/guanaco-392154568 and https://www.shutterstock.com/it/image-photo/guanaco-525268 and https://www.shutterstock.com/it/image-photo/guanacos-lama-guanicoe-female-cub-torres-1468689881 and https://www.shutterstock.com/it/image-photo/guanaco-torres-del-paine-national-park-1180913092 and https://www.shutterstock.com/it/image-photo/guanaco-torres-del-paine-national-park-72827194 and https://www.shutterstock.com/it/image-photo/guanaco-south-american-wildlife-patagonia-1462149629 and https://www.inaturalist.org/observations/67711685).

Of thousands of photos of the guanaco on the Web, the following shows a hypothetical facial/laryngeal flag most clearly (https://www.inaturalist.org/observations/98607391).

However, the darkness on the face is one of the most variable aspects of colouration in the guanaco, both regionally and individually. Furthermore, even more than in the vicuna (https://www.shutterstock.com/it/image-photo/pretty-llama-walking-green-meadow-28236070), the pallor on the side of the posterior part of the face is so small-scale (https://www.inaturalist.org/observations/98462641) that its effectiveness as a conspicuous feature is questionable.

POSSIBLE FIBULAR FLAG:

Please see https://www.inaturalist.org/journal/milewski/70368-a-new-feature-of-adaptive-colouration-in-ungulates-the-fibular-flag#.

The inner surfaces of the legs are so extensively and uniformly whitish in the guanaco that this far exceeds countershading (https://www.inaturalist.org/observations/81955507 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-patagonia-argentina-516764902 https://www.shutterstock.com/it/image-photo/guanaco-relative-llama-grazing-along-grasslands-1540586732 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-on-hill-1989759152 and https://www.shutterstock.com/it/image-photo/guanaco-torres-del-paine-chile-wild-648760288).

This suggests that the whitish inner surface of the upper hindleg, in particular, functions as a flag during walking (https://www.inaturalist.org/observations/10060027 and https://www.inaturalist.org/observations/1214422).

POSSIBLE POSTERIOR BLEEZE/FLAG:

The following is a reminder of the degree of conspicuousness of a posterior bleeze (Dama dama https://www.shutterstock.com/it/image-photo/deer-forest-1374230219).

In the guanaco, the buttocks, and the posterior surfaces of the forelegs, tend to be pale (https://www.shutterstock.com/it/image-photo/guanaco-side-looking-background-purple-pink-2101908997 and https://www.inaturalist.org/observations/34519891).

This is partly because the short pelage as well as the associated visible skin of the buttocks are depigmented - unlike the somewhat pigmented bare skin of the perineal area, around anus and vulva (see second photo in https://www.inaturalist.org/observations/69026331).

Furthermore, in those populations and individuals in which the pelage on the tail is dark, there is some degree of dark/pale contrast on the posterior aspect of the figure (https://www.shutterstock.com/it/image-photo/brown-white-guanaco-natural-environment-ocher-2196598343).

The pattern on the buttocks of the guanaco is usually more conspicuous than that in the vicuna (https://www.shutterstock.com/it/image-photo/group-wild-vicunas-andes-2071138874).

However, it is questionable whether this qualifies as a bleeze, even in the case of the guanaco.

This is because

• the pattern on the buttocks (which are narrow) is relatively small-scale (https://www.shutterstock.com/it/image-photo/guanacos-grass-fields-torres-del-paine-1410998639) and individually/regionally variable (https://www.inaturalist.org/observations/87232435),
• the darkness of the pelage of the tail is individually/regionally variable and, even in its maximal expression, brown rather than blackish, and
• the darkness of the perineal bare skin (exposed when the tail is raised) is limited (https://www.inaturalist.org/observations/45265653 and https://www.inaturalist.org/observations/70429726 and second photo in https://www.inaturalist.org/observations/78272881 and https://www.inaturalist.org/observations/76501642 and https://www.inaturalist.org/observations/61250026).

POSSIBLE FRONTAL BLEEZE:

The following is a reminder of the degree of conspicuousness of a frontal bleeze: Vicugna vicugna mensalis https://www.shutterstock.com/it/image-photo/portrait-wild-vicuna-arequipa-region-south-2131817439

In the guanaco, there are two features, on the front of the figure, that potentially function as large-scale advertisement (https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-patagonia-11002648).

These are pale surfaces

• on the chest and the front of the neck, where the pelage is woolly (https://www.shutterstock.com/it/image-photo/guanacos-lama-guanicoe-torres-del-paine-1775571674 and https://www.shutterstock.com/it/image-photo/group-guanacos-lama-guanicoe-steppe-torres-1581832945 and https://www.shutterstock.com/it/image-photo/guanaco-torres-del-paine-national-park-1169593093), and
• on the inner, upper forelegs, where the pelage is extremely short, and there is sharp contrast between pale and relative dark on the front of the upper forelegs (https://www.inaturalist.org/observations/144573654 and https://www.inaturalist.org/observations/98007846 and https://www.inaturalist.org/observations/96162020 and https://www.inaturalist.org/observations/64786909 and https://www.inaturalist.org/observations/47135996 and https://www.inaturalist.org/observations/41174994 and https://www.inaturalist.org/observations/19436589 and https://www.inaturalist.org/observations/149005239).

A difference between the guanaco and the vicuna is that the anterior surface of the neck is pale only in the former species.

The upright orientation of the long neck of the guanaco (https://www.shutterstock.com/it/image-photo/guanacos-la-pampa-argentina-536889943) makes it unlikely that this pale pelage functioning as countershading. Therefore, the real function may be to make the figure conspicuous.

Furthermore, the pale pelage on the neck is long enough that the conspicuousness applies also under backlit illumination (https://www.inaturalist.org/observations/51414334 and https://www.shutterstock.com/it/image-photo/beautiful-patagonia-chile-mammal-family-camelids-1549154981 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-steppes-patagonia-argentina-1295332438 and https://www.shutterstock.com/it/image-photo/three-amazing-guanacos-puppies-looks-camera-1347921581 and https://www.shutterstock.com/it/image-photo/guanacos-wildlife-national-park-torres-del-1094853107 and https://www.shutterstock.com/it/image-photo/guanaco-national-park-torres-del-paine-280431626 and https://www.inaturalist.org/observations/19546459).

However, it is questionable whether the guanaco qualifies as possessing a frontal bleeze.

This is because

• the pale on the neck is individually/regionally variable (https://www.inaturalist.org/observations/95587270 and https://www.shutterstock.com/it/image-photo/guanaco-looks-funny-gorgeous-mountains-background-2101908190 and https://www.inaturalist.org/observations/54484389), and
• the pattern on the anterior surface of the upper forelegs - which has yet to be explained - is shared with many unrelated species of ruminants, in which the case for a frontal bleeze is even more tenuous (https://www.inaturalist.org/observations/54888783 and https://www.alamy.com/common-duiker-sylvicapra-grimmia-mkuze-game-reserve-kwazulu-natal-south-africa-image417606974.html?imageid=BE8AC823-F67D-4B37-BE27-261F9D9FE557&p=12455&pn=1&searchId=c1eaa6f64a0c4b761ce7e34454d6978c&searchtype=0 and https://www.imago-images.com/st/0059604126).

COMPLEXITY OF PELAGE/BARE SKIN AT ABDOMEN, ELBOW, BUTTOCKS, AND UNDER-TAIL

There is an intriguing aspect of the anatomy of the guanaco, located at the abdomen ('inguinal'), near the elbow ('axillary'), on the buttocks, and on the ventral surface of the tail.

This is

• the sharp differentiation of long pelage from apparently bare skin, and
• the difference between the pale skin of groin, buttocks, and tail and the dark skin of the perineum.

The main function of the pale, apparently bare skin (which also seems to occur on the inner surface of the upper forelegs) seems to be thermoregulation, rather than display by means of colouration.

When the animal stands under normal conditions, the panels of apparently bare skin are 'closed', by virtue of

• slight hunching of the torso, which keeps the upper hindlegs and elbow close to the torso (https://www.mediastorehouse.com.au/nature-picture-library/2019-december-highlights/rf-guanaco-lama-guanicoe-standing-mountain-19737708.html), and
• relaxation of the tail, which covers the bare skin of both the ventral surface of the tail and the perineal area (https://www.shutterstock.com/it/image-photo/curious-guanaco-lama-guanicoe-endless-grass-1226553520).

However, when the slight hunching of the torso is relaxed, what becomes visible is the clear distinction between the ventral pelage and the apparently bare skin,

• posterior to the belly (https://www.shutterstock.com/it/image-photo/guanako-stands-guard-front-mountains-blue-1459757072 and https://www.shutterstock.com/it/image-photo/guanaco-ischigualasto-nature-park-1226606107 and https://www.inaturalist.org/observations/122312497 and https://www.shutterstock.com/it/image-photo/guanaco-standing-on-top-hill-dark-2101909417 and https://www.inaturalist.org/observations/106039959), and
• posterior to the elbow (https://www.inaturalist.org/observations/66334242 and https://www.inaturalist.org/observations/107250616).

These apparently bare surfaces presumably function to regulate body heat, via perspiration (https://pubmed.ncbi.nlm.nih.gov/11163922/ and https://www.sciencedirect.com/science/article/abs/pii/S0306456500000140 and https://www.researchgate.net/publication/12165924_Sweating_in_the_guanaco_Lama_guanicoe and https://www.researchgate.net/figure/Scheme-of-a-guanaco-and-the-topographic-areas-where-skin-samples-were-taken1-inner_fig3_231316047) and radiation. In cold weather, the apparently bare panels can be covered, mainly by postural adjustments including the 'clamping' of the tail.

Few ungulates on Earth possess this mechanism, which may be related to the unusually narrow 'waist' of camelids (https://www.inaturalist.org/observations/61249739 and https://www.inaturalist.org/observations/61250535).

At first glance, there is little remarkable about the pale tract on the abdomen in the following (https://www.inaturalist.org/observations/146611617 and https://www.inaturalist.org/observations/123748337).

However, on closer scrutiny it can be seen that there is a considerable area of pale, apparently bare skin. There is another, similar but smaller, patch of pale, apparently bare skin just posterior to the elbow.

From the viewpoint of colouration:
A remarkable aspect of this anatomical configuration is that the skin is so depigmented that, even when maximally exposed, it does not detract from the conspicuous pallor of the flanks (https://www.inaturalist.org/observations/41904227 and https://www.inaturalist.org/observations/107503431 and https://www.inaturalist.org/observations/77991631 and https://www.inaturalist.org/observations/74556475 and https://www.inaturalist.org/observations/65433399).

to be continued in https://www.inaturalist.org/journal/milewski/75389-subtle-and-multifaceted-adaptive-colouration-in-the-largest-wild-ruminant-in-south-america-the-guanaco-lama-guanicoe-part-2#...

Publicado el febrero 14, 2023 04:22 TARDE por milewski