The bambis, part 8: adaptive colouration in grysboks, Raphicerus melanotis and Raphicerus sharpei

@capracornelius @tandala @oviscanadensis_connerties @jeremygilmore @paradoxornithidae @beartracker @jacqueline_llerena @henrydelange @tonyrebelo @koosretief @justinhawthorne @ludwig_muller @happyasacupcake @marcelo_aranda @enricotosto96 @diegoalmendras @michaelweymann @fionahellmann

...continued from https://www.inaturalist.org/journal/milewski/58139-the-bambis-part-7-why-do-certain-genera-show-tropical-hues#

Grysboks (Raphicerus melanotis https://es.123rf.com/photo_39925015_a-rare-cape-grysbok-antelope-raphicerus-melanotis-south-africa.html and https://www.inaturalist.org/observations/72612861) and Raphicerus sharpei (https://www.shutterstock.com/image-photo/sharpes-grysbok-antelope-794728726 and https://www.alamy.com/stock-photo-sharpes-grysbok-31791328.html?imageid=8258088A-BE1C-47D2-B568-B4E03D47F25D&p=34420&pn=1&searchId=bb39c60edd2f811fc9c03d99a5112e0b&searchtype=0 and https://www.shutterstock.com/image-photo/sharpes-grysbok-hiding-thick-green-undergrowth-2178590039) occur in the southern and southeastern parts of Africa.

Among all the ungulates of the world, these are among the best examples of thoroughly inconspicuous colouration, of a cryptic type (https://en.wikipedia.org/wiki/Crypsis).

Grysboks are nocturnal and non-gregarious, and depend on shrubby vegetation for cover.

This means that the colouration is so plain and featureless that the figures blend extremely well into the environment (https://www.inaturalist.org/observations/11178739 and https://www.inaturalist.org/observations/48569125 and https://commons.wikimedia.org/wiki/File:Sharpe%27s_Grysbok.jpg and https://www.shutterstock.com/image-photo/sharps-grysbok-kruger-1083039092).

Even more so, when one considers that any differentiation in hues (rufous ground-colour vs grey on the posterior surface of the ears, https://www.inaturalist.org/observations/68999756) are probably invisible in the eyes of the relevant animals (i.e. grysboks themselves, and the Carnivora that are their main predators).

On one hand, this seems to make grysboks the simplest - and least interesting - of ungulates for further investigation, in terms of adaptive colouration.

However, I take a more curious approach.

What the simplicity of the colouration of grysboks means is that we have an opportunity to clarify any small-scale features that do not conform to the overall plainness.

These anomalous features (*asterisk indicates individual variation) are

BODY

Many species of mammals have grizzled/speckled pelage, in which each hair is graduated in colour from the base to the tip (https://en.wikipedia.org/wiki/Fur#/media/File:Down_Awn_and_guard_hairs_of_cat_2012_11_13_9203r.JPG).

However, in grysboks the form of grizzing is, as far as I know, unique among ruminants. This is because each hair is homogeneous in colour, but a minor percentage of the hairs are whitish.

Countershading (https://en.wikipedia.org/wiki/Countershading) is better-developed in R. sharpei than in R. melanotis. This is unsurprising, based on similar latitudinal patterns in various other ruminants (https://www.inaturalist.org/journal/milewski/53696-a-succinct-photo-guide-to-subspecies-of-the-bush-duiker#).

FACE, HEAD and EARS

The face of grysboks is not plain-coloured. One of the best illustrations of the pattern can be found by scrolling in https://www.edwardselfephotosafaris.com/newsp27.html.

All ruminants with a bare rhinarium have the nose dark-pigmented. However, the following of Cephalophus shows that the colouration of the face can otherwise be plain in small-bodied ruminants: https://www.dreamstime.com/stock-photo-duiker-close-up-detail-small-west-african-antelope-image75691614.

My interpretation is as follows:

The various markings on the face have dual functions at different scales.

When viewed from some distance, they amount collectively to a form of disruptive colouration, 'camouflaging' the head by disrupting its shape.

However, the same markings can also function, at close range, for social communication, e.g. aiding individual recognition.

Grysboks differ from their congener, Raphicerus campestris, in that the whitish pelage adjacent to the eye (https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=2&get_facets=0&search_type=pagination&asset_id=333179556) has been eclipsed.

I suspect that this has occurred not by means of any darkening of the hairs, but rather by a thinning of the pelage, exposing the blackish skin (https://www.redbubble.com/people/mags/works/7400304-the-tiny-shy-scarce-sharpe-s-grysbok-raphicerus-sharpei-kruger-national-park).

The ear pinna is large in all spp. of Raphicerus, probably for thermoregulation as much as hearing.

However, it is puzzling that the hair-curtains, which open and close ostensibly in reaction to temperature, are not a brownish colour, which would make the front-of-ear inconspicuously plain.

Instead, the hair-curtains are pale enough to be conspicuous at distances potentially relevant to scanning predators (https://www.inaturalist.org/observations/21208569 and https://www.inaturalist.org/observations/7026104).

This puzzle deserves further thought, as does the individually variable paleness on the front of the neck.

The following show the pale hair-curtains on front-of-ear

The paleness of the lower lip and chin is poorly explained by countershading.

I interpret the colouration around the mouth in both spp. to be a buccal semet (https://www.inaturalist.org/observations/11263147 and https://www.alamy.com/sharpes-grysbok-raphicerus-sharpei-south-africa-mpumalanga-kruger-national-park-image255383147.html?imageid=B2DB3495-B84D-45B8-93F0-CADC61B7296C&p=853443&pn=1&searchId=bb39c60edd2f811fc9c03d99a5112e0b&searchtype=0 and https://www.alamy.com/stock-photo-portrait-of-sharpes-grysbok-raphicerus-sharpei-in-the-bush-the-photo-33096574.html?imageid=097746CA-48F5-40A6-8578-BFE7EBA82631&p=60598&pn=1&searchId=bb39c60edd2f811fc9c03d99a5112e0b&searchtype=0). Please note, in the following view (https://www.inaturalist.org/observations/13582069), that the lower lip and adjacent pelage is the only part of the figure that is whitish.

This small-scale pattern may possibly be more conspicuous in ultraviolet than in the range of wavelengths visible in human eyes.

FEET

The following is possibly the most unexpected of my findings in this Post.

Raphicerus sharpei, in at least some individuals, has anomalously pale feet, which possibly function as a pedal flag. I have, as yet, no explanation for why there is no such feature in either R. melanotis or R. campestris.

However, R. sharpei also happens to differ from R. melanotis in

So, what emerges is that one of the main differences between the two spp. of grysboks is in the feet, including their anatomy, colouration, and action in producing an audial and possibly visual signal in an anti-predator context.

to be continued in https://www.inaturalist.org/journal/milewski/70293-the-bambis-part-9-bleezes-flags-and-semets-in-the-bovid-genus-raphicerus#...

Publicado por milewski milewski, 23 de septiembre de 2022

Comentarios

RAPHICERUS CAMPESTRIS:

Front-of-ear with pale hair-curtains closed:

https://stock.adobe.com/search?k=steenbok&asset_id=505717039

https://stock.adobe.com/search?k=steenbok&asset_id=43651464

https://stock.adobe.com/search?k=steenbok&asset_id=83926648

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=2&get_facets=0&search_type=pagination&asset_id=310160454

Front-of-ear with pale hair-curtains partly open:

https://stock.adobe.com/search?k=steenbok&asset_id=210184395

Front-of-ear with pale hair-curtains fully open:

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=132701922

Buccal semet:

https://stock.adobe.com/search?k=steenbok&asset_id=396571930

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=361471688

Publicado por milewski hace 5 días (Marca)

I am puzzled by the bareness of the front-of-ear in this specimen of Raphicerus melanotis:
https://www.zoochat.com/community/media/cape-or-southern-grysbok-raphicerus-melanotis.486198/

Publicado por milewski hace 5 días (Marca)

Raphicerus campestris differs from grysboks in having white inner buttocks:

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=441156073

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=526322906

These can be further exposed by flaring (piloerection) of the adjacent brownish pelage of the outer buttocks:

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=2&get_facets=0&search_type=pagination&asset_id=441230341

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=180230559

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=180230715

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=466446514

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=476713200

Publicado por milewski hace 5 días (Marca)

The following shows the complexity of the colouration on the mandible in Raphicerus campestris:

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=378593532

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=4&search_type=pagination&get_facets=0&asset_id=378593486

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=378593613

https://stock.adobe.com/search?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=1&filters%5Bcontent_type%3Atemplate%5D=1&filters%5Bcontent_type%3A3d%5D=1&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=0&filters%5Bcontent_type%3Aimage%5D=1&k=steenbok&order=relevance&safe_search=1&limit=100&search_page=5&search_type=pagination&get_facets=0&asset_id=378593575

Publicado por milewski hace 5 días (Marca)

I have not detected any auricular semet in any species of Raphicerus. However, the following, of Raphicerus melanotis, shows a slight tendency to pale at the bases of the ear pinnae:

https://www.inaturalist.org/observations/71202515

Publicado por milewski hace 5 días (Marca)
Publicado por milewski hace 5 días (Marca)

@mileswki
I believe it to be a mature female from the Axis porcinus complex.

Publicado por capracornelius hace 5 días (Marca)

The following (https://www.capetownetc.com/cape-town/baby-grysbok-spotted-on-camera/) shows several aspects of Raphicerus melanotis.

The colouration is identical in adult and infant.

The paleness of the lateral surface of the mandible is anomalous, relative to the principle of countershading.

The false hooves are so small, in this species, that they are barely visible even in this exceptionally close-up photo.

Publicado por milewski hace 5 días (Marca)

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