Subtle and multifaceted adaptive colouration in the largest wild ruminant in South America: the guanaco (Lama guanicoe), part 2

...continued from https://www.inaturalist.org/journal/milewski/75256-subtle-and-multifaceted-adaptive-colouration-in-the-largest-wild-ruminant-in-south-america-the-guanaco-lama-guanicoe-part-1#

In part 1, I have described the larger-scale features of adaptive colouration in the guanaco. Here, I describe the smaller-scale features, followed by an overall discussion.

POSSIBLE CAUDAL FLAG:

The following is a reminder of how conspicuous a caudal flag can be: Odocoileus virginianus https://wdfw.wa.gov/species-habitats/species/odocoileus-virginianus-leucurus.

The tail of the guanaco tends to be somewhat dark (https://www.inaturalist.org/observations/143882795).

It is also habitually raised, to varying degrees and in various circumstances (https://www.inaturalist.org/observations/9956653 and https://www.westend61.de/en/imageView/FOF002916/south-america-chile-patagonia-guanacos-in-torres-del-paine-national-park and https://www.shutterstock.com/it/image-photo/guanaco-parque-luro-nature-reserve-la-1904100052 and https://www.inaturalist.org/observations/148456176 and https://www.inaturalist.org/observations/141173000).

However, there is much individual/regional variation in the size and tone of the tail.

Furthermore, the bare skin on the ventral surface of the tail, visible when the tail is raised, is inconspicuously pale (https://www.inaturalist.org/observations/69735055 and https://www.inaturalist.org/observations/126889604 and https://www.inaturalist.org/observations/145758231 and https://www.inaturalist.org/observations/21321419).

The following shows the maximum size and darkness of the tail (https://www.inaturalist.org/observations/59737148).

The following show the minimum size and darkness of the tail (https://www.inaturalist.org/observations/55603034 and https://www.inaturalist.org/observations/32918899 and https://www.inaturalist.org/observations/44806476 and https://www.inaturalist.org/observations/105626932 and https://www.inaturalist.org/observations/97562639 and https://www.inaturalist.org/observations/19546312).

Overall, the case for a caudal flag is weak. The tail certainly has functions in signalling/self-advertisement in the guanaco. However, what is ambivalent is the degree to which colouration plays a role in this.

POSSIBLE PEDAL FLAG:

The following is a reminder of how conspicuous a pedal flag can be: Boselaphus tragocamelus https://www.flickr.com/photos/cirdan-travels/48675416448.

The lower legs of the guanaco may be pale, in a way that is potentially conspicuous, particularly when the limbs move (https://www.inaturalist.org/observations/123266443 and https://www.inaturalist.org/observations/129227204 and https://www.inaturalist.org/observations/114424972 and https://www.inaturalist.org/observations/139979140 and https://www.inaturalist.org/observations/102997898).

However, this is inconsistent among individuals and populations (https://www.inaturalist.org/observations/108379179 and https://www.inaturalist.org/observations/147915290 and https://www.inaturalist.org/observations/121451241 and https://www.shutterstock.com/it/image-photo/guanacos-roaming-arid-altiplano-landscape-near-2151990071).

Because the feet do not have conspicuous colouration in most individuals/regions, I doubt that the guanaco qualifies as possessing a pedal flag.

POSSIBLE AURICULAR SEMET:

There seems to be a sheen effect on the posterior surface of the ear pinnae in the guanaco (https://www.inaturalist.org/observations/52204973 and https://www.inaturalist.org/observations/98011389 and https://www.inaturalist.org/observations/93318347 and https://www.inaturalist.org/observations/60795995 and https://www.inaturalist.org/observations/40917644).

The anterior surface of the ear pinnae is also conspicuously pale in some views (https://www.inaturalist.org/observations/3034784 and https://www.shutterstock.com/it/image-photo/single-guanaco-on-highway-patagonia-mountains-625124627 and https://www.inaturalist.org/observations/39805135).

In northern populations, the ear pinnae in some individuals are dark (https://www.inaturalist.org/observations/4522872 and https://www.inaturalist.org/observations/32431037).

However, the conspicuousness of the ear pinnae is limited, owing to their small size (https://www.inaturalist.org/observations/70619726 and https://www.inaturalist.org/observations/62258944 and https://www.inaturalist.org/observations/106996094 and https://www.inaturalist.org/observations/44917500).

Populations in/near the Atacama Desert may have the largest ear pinnae (https://www.inaturalist.org/observations/33042947 and https://www.inaturalist.org/observations/9822543).

A case can be made that the colouration of the ear pinnae in the guanaco qualifies as an auricular semet, expressing emotion in close-range social (intraspecific) interactions (https://www.inaturalist.org/observations/89238468 and https://www.inaturalist.org/observations/36562604). However, this is undermined by the regional occurrence of individuals in which the ear pinnae are as dark as the rest of the head.

DISCUSSION AND SUMMARY:

The maximum similarity in colouration between the guanaco (https://www.shutterstock.com/it/image-photo/group-guanaco-lama-guanicoe-grazing-on-776986573 and https://www.inaturalist.org/observations/105626932) and the vicuna (https://www.inaturalist.org/observations/79058821) is considerable.

It is testimony to the similarity in colouration between the guanaco and V. v. vicugna that dozens of photos of the latter are mislabelled as the former on the Web.

Overall, the most significant, and least ambivalent, of the features of adaptive colouration in the guanaco is the pale of the posterior flank (https://www.inaturalist.org/observations/50836549 and https://www.inaturalist.org/observations/147930621 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-patagonia-61999597 and https://www.shutterstock.com/it/image-photo/group-guanacos-roaming-bushland-against-hazy-2158956455 and https://www.inaturalist.org/observations/123266439).

This feature, as in the vicuna, is 'caleonic' in origin (https://www.inaturalist.org/journal/milewski/67529-caleonic-colouration-in-the-caribou-part-1-rangifer-tarandus-terranovae#).

The postulated lateral bleeze of the guanaco (which functions also anterio- and posteriolaterally) resembles a feature of conspicuous colouration in the southern, nominate subspecies of the vicuna, viz., V. v. vicugna (https://www.shutterstock.com/it/image-photo/two-guanacos-heads-down-eating-atacama-2146328725 and https://www.shutterstock.com/it/image-photo/vicuna-vicgna-vicugna-high-altitude-camelid-22334845 and https://www.shutterstock.com/it/image-photo/guanaco-middle-atacama-desert-chile-1893077476 and https://www.shutterstock.com/it/image-photo/guanaco-lama-guanicoe-patagonia-264363041 and https://www.shutterstock.com/it/image-photo/two-guanacos-posing-photo-1718861740 and https://www.shutterstock.com/it/image-photo/lonely-guanaco-walking-on-rocks-chile-1595227213 and https://www.shutterstock.com/it/image-photo/guanacos-searching-food-atacama-desert-chile-1286391754).

However, even this caleonic, relatively large-scale feature is too inconsistent for the guanaco, as a species overall, to qualify as possessing unambivalently conspicuous colouration.

I hesitate to invoke subspecies in the case of the guanaco.

However, my finding is that the northern populations have the least conspicuous colouration, with the possible exception of a dark head (https://www.inaturalist.org/observations/50710723 and https://www.inaturalist.org/observations/40923890 and https://www.inaturalist.org/observations/9589820 and https://www.inaturalist.org/observations/9079851 and https://www.inaturalist.org/observations/7664369 and https://www.inaturalist.org/observations/4841699 and https://www.inaturalist.org/observations/4525711).

Posted on 18 February, 2023 01:23 by milewski milewski

Comments

@hardinglee

Dear Lee, I have noticed that, in the nearly 2000 observations of the guanaco in iNaturalist, you are the only observer to comment particularly on the differences between the northern and southern populations. So, I trust that you will find my descriptions, in this two-part Post, to be informative, with kind regards from Antoni

Posted by milewski over 1 year ago

The following nicely illustrates the postulated posterior bleeze, and laryngeal flag in the guanaco:

https://www.istockphoto.com/photo/guanacos-at-el-calafate-highlands-gm1447145587-485036163?phrase=guanaco

Posted by milewski over 1 year ago

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