Adaptive colouration in the vicuna (Camelidae: Vicugna vicugna)

Please see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562099/.

The vicuna (Vicugna vicugna, https://www.shutterstock.com/image-photo/vicuna-arid-landscape-chimborazo-nature-reserve-603780842 and https://www.inaturalist.org/observations/69950772 and https://en.wikipedia.org/wiki/Vicuna and https://animaldiversity.org/accounts/Vicugna_vicugna/) has woolly pelage, adapted to the snow-free cold at high altitudes in the Andean altiplano (https://en.wikipedia.org/wiki/Altiplano).

Please see https://www.nwf.org/Magazines/National-Wildlife/2002/Return-of-the-Golden-Fleece and https://critterfacts.com/vicuna/ and http://elelur.com/mammals/vicuna.html and https://www.bioexpedition.com/vicuna/ and https://www.nationalparks-worldwide.com/sam/peru/national-parks/vicunas/vicunas.html.

Nothing seems previously to have been written about the adaptive colouration of this, the smallest of camelids (https://escholarship.org/content/qt7xs9j2zs/qt7xs9j2zs.pdf).

DIFFERENCE BETWEEN SUBSPECIES:

The vicuna has

a northern subspecies (Vicugna vicugna mensalis, https://www.inaturalist.org/observations/24628273 and https://www.inaturalist.org/observations/146554711 and https://www.inaturalist.org/observations/29370776 and https://www.inaturalist.org/observations/63153268 and https://www.inaturalist.org/observations/39681178 and https://www.inaturalist.org/observations/20726313 and https://www.inaturalist.org/observations/29951908 and https://www.inaturalist.org/observations/30211603), and
a southern subspecies (Vicugna vicugna vicugna, https://www.inaturalist.org/observations/61325069 and https://www.inaturalist.org/observations/144730490 and https://www.inaturalist.org/observations/37256776).

The two differ in their patterns of colouration, as follows:

the northern ssp. has a frontal bleeze, viz. conspicuous pale on and near the chest (https://www.inaturalist.org/observations/125027521 and https://www.inaturalist.org/observations/35712868), whereas
the southern ssp. has 'caleonic' colouration (https://www.inaturalist.org/observations/36832325 and https://www.inaturalist.org/journal/milewski/67529-caleonic-colouration-in-the-caribou-part-1-rangifer-tarandus-terranovae#), in which the pale of the ventral surface extends upwards on to the sides of the body, particularly the hips.

CONCEPTUAL FRAMEWORK:

The vicuna depends on short vegetation, and is diurnal and gregarious (https://www.istockphoto.com/photo/vicuna-gm529652033-54217656?phrase=vicuna%20and%20young%20in%20lauca%20national%20park).

It would, therefore, be unsurprising if - based on the trends seen in comparable deer and bovids - the pelage of the vicugna were to have conspicuous features of pigmentation/depigmentation.

And indeed, the colouration of the vicuna is such that it tends to stand out from its environment. This is by means of large-scale pale features of the pelage.

However:
What is surprising is the position of the most conspicuous feature of the colouration of the northern ssp.
This is located on the front of the figure (Vicugna vicugna mensalis: https://www.alamy.com/vicua-and-the-volcano-misti-reserva-nacional-salinas-y-aguada-blancaper-image357300976.html?imageid=79108214-DCF7-48E4-A45A-28C871E28077&p=16583&pn=1&searchId=29cecb4231d7c99f92316b37750496dd&searchtype=0).

Most comparable deer and bovids emphasise the posterior, not the anterior, of the figure. The northern ssp. of the vicuna instead combines a frontal bleeze, centred on the chest, with otherwise fairly plain colouration in both sexes.

The pattern seen in the northern ssp. of the vicuna thus differs from that in any other ungulate.

FRONTAL BLEEZE:

The frontal bleeze of the northern ssp. of the vicuna (https://www.mediastorehouse.com.au/ardea-wildlife-pets-environment/fg-aj-105-1303400.html) is an adaptively conspicuous feature, consisting of the following elements:

a large patch of pale, particularly long, pelage, which adorns a broad area of the anatomy, about the chest (https://www.shutterstock.com/image-photo/one-vicuna-walking-across-other-vicunas-12819937 and https://www.shutterstock.com/image-photo/vicuna-chaccu-highlands-peru-1661486827 and https://www.shutterstock.com/image-photo/vicuna-aguada-blanca-arequipa-peru-142584217), and
whitish, short pelage on the anterior surfaces of the upper forelegs, which effectively extends the pale front in a ventral direction (https://photos.com/featured/two-vicunas-vicugna-vicugna-nuzzling-art-wolfe.html and https://www.inaturalist.org/observations/68894248 and https://www.shutterstock.com/image-photo/vicunas-peruvian-andes-arequipa-peru-173382041 and https://www.shutterstock.com/image-photo/vicuna-peruvian-andes-arequipa-peru-176104835 and https://www.inaturalist.org/observations/38583485).

The frontal bleeze is conspicuous

This is true notwithstanding the fact that no part of the pelage of the vicuna is dark enough to provide particular contrast to the pale surfaces.

CALEONIC COLOURATION:

In the southern subspecies of the vicuna, the pale of the ventral surface of the torso has been extended upwards, anterior and posterior to both the shoulders/scapula and the haunch/upper hindleg.

This results in pale pelage extending broadly and diffusely on to

the junction of neck and torso,
above the elbow,
from groin to hips, and
on the buttocks.

Please compare the vicugna with a typical example of caleonic colouration, namely Equus khur:
https://stock.adobe.com/images/indian-wild-asses-equus-hemionus-khur-also-known-as-baluchi-wild-ass-in-the-raan-of-kutch-a-saline-desert-in-gujarat-the-last-natural-sanctuary-for-this-sub-species-of-wild-ass/239537503 and https://fineartamerica.com/featured/1-indian-wild-ass-equus-hemionus-khur-pete-oxford.html.

The following illustrate caleonic colouration in the southern subspecies of the vicuna:
https://www.inaturalist.org/observations/121600503 and https://www.inaturalist.org/observations/88307462 and https://www.shutterstock.com/image-photo/vicunas-salar-de-tara-desert-atacama-112162280 and https://www.inaturalist.org/observations/141842864 and https://www.inaturalist.org/observations/141842863 and https://www.inaturalist.org/observations/38702920 and https://www.inaturalist.org/observations/141842865 and https://www.shutterstock.com/image-photo/group-vicunas-99233132 and https://www.shutterstock.com/image-photo/vicuna-vicgna-vicugna-high-altitude-camelid-22334845 and https://www.shutterstock.com/image-photo/portrait-vicuna-vicugna-by-chalviri-lagoon-1999882352 and https://www.inaturalist.org/observations/47665170 and https://www.shutterstock.com/image-photo/vicuna-vicgna-vicugna-high-altitude-camelid-22503727.

Caleonic colouration in the vicuna results in both

the de-emphasis of the pale frontal pelage, and
the emphasis of the pale tract on the hips (ileum) in particular.

FACIAL FLAG:

The cheeks of the vicuna (https://www.shutterstock.com/image-photo/portrait-vicuna-vicugna-selective-focus-2145439021) are pale/sheeny enough to be noticeable in many views, This is likely to add to the conspicuousness of the figure (https://pavonivaganti.com/en/vicuna-what-it-is/ and https://www.inaturalist.org/observations/43003648), particularly when the head is moved.

The facial flag qualifies as a conspicuous feature, notwithstanding that

the head is remarkably small, relative to the proportions seen in comparable deer and bovids,
the paleness of the cheeks seems to be owing partly to a sheen effect rather than depigmentation,
the neck is so long that it widely separates the cheeks from the pale chest, and
there is no contrasting dark on the head, other than the eyes.

The following shows that, in certain illumination, the cheeks are not noticeably pale: https://andrebaertschi.photoshelter.com/image/I0000SbSgFVcjZPU.

The following is a particularly clear illustration of the hypothetical sheen-effect on the cheek in the southern ssp., V. v. vicugna: https://www.inaturalist.org/observations/61325869.

The following are comparable views, lacking the sheen-effect: https://www.inaturalist.org/observations/107312217 and https://www.inaturalist.org/observations/139067636 and https://www.inaturalist.org/observations/66795801 and https://www.inaturalist.org/observations/146260487 and https://www.inaturalist.org/observations/105434200 and https://www.inaturalist.org/observations/140082618 and https://www.inaturalist.org/observations/37686762.

The following show what is probably the true (modest) degree of depigmentation of the cheeks: https://www.inaturalist.org/observations/141842864.

The following seems to show the sheen-effect in partial effect: https://www.inaturalist.org/observations/140837038.

INCONSPICUOUS HINDQUARTERS:

No pattern on the rump/buttocks of the vicuna seems conspicuous enough to qualify as a bleeze or flag.

This holds true for both subspecies:

northern (V. v. mensalis) https://www.shutterstock.com/image-photo/vicuna-vicugna-wild-south-american-camelid-163024664 and https://www.inaturalist.org/observations/18851909 and https://www.inaturalist.org/observations/135523782 and https://www.inaturalist.org/observations/68809821 and https://www.inaturalist.org/observations/38739255 and https://www.inaturalist.org/observations/67319990
southern (V. v. vicugna) https://www.inaturalist.org/observations/52640439 and https://www.inaturalist.org/observations/39408908 and https://www.inaturalist.org/observations/103617990 and https://www.inaturalist.org/observations/148323868).

The relative inconspicuousness of the hindquarters holds, notwithstanding the facts that

the caleonic pattern highlights the hips in the southern subspecies, and
the tip of the tail is white (https://www.inaturalist.org/observations/61326277).

The following show the white tail-tip in the two subspecies:

COMPARISON WITH GUANACO:

The guanaco (Lama guanicoe, https://www.inaturalist.org/taxa/42240-Lama-guanicoe) is worth comparing with the vicuna, because

the two genera are closely related, with similar anatomy and body-proportions,
both live in open environments,
the guanaco lives mainly in the Andes, and
both species have caleonic patterns of colouration (https://www.inaturalist.org/observations/15178773 and https://commons.wikimedia.org/wiki/File:Vicu%C3%B1a_-_Chimborazo,_Ecuador.jpg and https://www.shutterstock.com/image-photo/vicunas-142909450 and https://www.inaturalist.org/observations/45111163).

The southern subspecies of the vicuna resembles the guanaco in its colouration, apart from the lack of any dark on tail or face (https://www.inaturalist.org/observations/61325069).

For the two species overall, the main differences are that

the guanaco has relatively conspicuous hindquarters, including a dark tail that tends to be raised (https://justfunfacts.com/wp-content/uploads/2018/01/guanaco.jpg),
the caleonic pattern on the posterior-flank, and dorsal to the knee (https://www.shutterstock.com/image-photo/magic-country-patagonia-national-park-torres-258938486 and https://www.shutterstock.com/image-photo/beautiful-patagonia-chile-mammal-family-camelids-1549154981), is much better-developed in the guanaco than in the northern subspecies of the vicuna.

WHY DOES THE NORTHERN SUBSPECIES OF THE VICUNA ADVERTISE ITSELF FRONTALLY?

The habitat of the vicuna is relatively free from predators. This is because

South America as a whole has relatively few large carnivores,
the Andes are relatively remote and quasi-insular, and
within the Andes, the vicuna prefers plains offering minimal cover to predators.

This relative freedom from predation is consistent with

the slow reproduction of camelids, including the vicuna (see comment in https://www.inaturalist.org/journal/milewski/73914-kangaroos-breed-slowly-compared-to-ruminants#),
the relative tameness of the vicuna towards humans, to the degree that this species allows itself to be rounded up every few years for the shearing of its wool, and
the occurrence of stotting behaviour (https://en.wikipedia.org/wiki/Stotting and https://www.academia.edu/16199436/The_Social_Behavior_of_the_Vicu%C3%B1a_p_477_ and https://www.researchgate.net/profile/Bibiana-Vila/publication/248444166_Aspects_of_play_behaviour_of_vicuna_Vicugna_vicugna/links/5ebfe953299bf1c09ac0c98a/Aspects-of-play-behaviour-of-vicuna-Vicugna-vicugna.pdf and https://www.sciencedirect.com/science/article/abs/pii/0921448894900485 and https://www.researchgate.net/publication/248444166_Aspects_of_play_behaviour_of_vicuna_Vicugna_vicugna), but not necessarily in an anti-predator context.

Bleezes and flags function as signals to both conspecifics and predators. In most deer and bovids possessing bleezes and flags, two of the functions of these features are to signal that

the individual/group has spotted the predator and is alert and ready to flee, and
the individual is fit and thus unlikely to be pursued successfully.

Given the communication with predators, it makes sense that most deer or bovids emphasise the hindquarters in their conspicuous displays.

However, in the case of the vicuna, most signalling is instead likely to be intraspecific/social, and free of implications of imminent flight.

Therefore, it may make sense that the main conspicuous feature on the figure is frontal, facilitating communication in contexts other than encounters with predators.

However, this does not explain the lack of the frontal bleeze in the southern subspecies. Do readers have better ideas?

Also see:
https://www.inaturalist.org/journal/milewski/75011-observations-in-inaturalist-remain-insufficient-to-draw-the-border-between-the-two-subspecies-of-the-vicuna#
https://www.inaturalist.org/posts/75256-subtle-and-multifaceted-adaptive-colouration-in-the-largest-wild-ruminant-in-south-america-the-guanaco-lama-guanicoe#
https://www.inaturalist.org/journal/milewski/75397-comments-on-subspeciation-in-the-wild-camelids-of-south-america#

Publicado el enero 28, 2023 10:11 MAÑANA por