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

• * symmetrical, dark marking on the crown, particularly in females (https://www.inaturalist.org/observations/78840233 and https://www.mindenpictures.com/stock-photo-sharpe-s-grysbok-raphicerus-sharpei--kruger-national-park-south-africa-naturephotography-image00592390.html and https://www.shutterstock.com/image-photo/sharpes-grysbok-feeding-on-leaf-litter-1591922956)
• * dark around the eyes (https://www.inaturalist.org/observations/84551438 and https://www.shutterstock.com/image-photo/sharpes-grysbok-southern-african-savanna-1248555415 and https://www.zoonar.de/photo/sharpegreisbock-im-kruger-nationalpark-sdafrika-sharpes-grysbok-in-south-africa-raphicerus-sharpei_6700501.html and https://www.alamy.com/stock-photo-portrait-of-sharpes-grysbok-raphicerus-sharpei-in-the-bush-the-photo-33096566.html?imageid=45F45224-33EF-42D1-BE9B-A0447082D0A6&p=60598&pn=1&searchId=bb39c60edd2f811fc9c03d99a5112e0b&searchtype=0 and https://www.inaturalist.org/observations/95960111)
• pale lower lips (contrasting with the dark, bare edge of the lower lips) and chin, extending to the lateral surface of the mandible (https://www.dreamstime.com/stock-photos-grysbok-antelope-image13753523 and https://www.dreamstime.com/royalty-free-stock-images-grysbok-antelope-image10975479 and https://www.inaturalist.org/observations/109231230 and https://www.inaturalist.org/observations/25204164 and https://www.inaturalist.org/observations/90688968)
• pale upper lips, mainly in R. sharpei (https://www.inaturalist.org/observations/19128418 and https://www.alamy.com/sharpes-grysbok-raphicerus-sharpei-kruger-national-park-south-africa-image417606985.html)
• * dark on the rostrum, adjacent to the rhinarium (https://en.wikipedia.org/wiki/Rhinarium)
• pale hair-curtains on the anterior surface of the ear pinnae (https://www.inaturalist.org/observations/76206461 and https://www.inaturalist.org/observations/63753739)

• whitish of variable extent on the throat (https://www.africahunting.com/media/cape-grysbok-tiny-ten-full-mount-taxidermy.50587/
  and https://www.flickr.com/photos/brinksview/24997270338 and https://www.inaturalist.org/observations/10935808 and https://m.facebook.com/BLphotography/photos/a-beautiful-sharpes-grysbok-which-is-the-smallest-antelope-found-in-south-luangw/10156401808757698/ and https://www.shutterstock.com/image-photo/sharpe-grysbok-kruger-national-park-south-1157443249 and https://www.istockphoto.com/photo/sharps-grysbok-antelope-in-front-of-a-thorn-bush-gm693678254-128137499?phrase=grysbok)

• grizzling of the main pelage of the body in the form of whitish whole hairs interspersed in a matrix of rufous hairs (https://www.inaturalist.org/observations/94093283 and https://www.shutterstock.com/image-photo/sharpes-grysbok-feeding-on-leaf-litter-1591922947)
• * pale on the feet, particularly the hind feet, in R. sharpei only (https://www.inaturalist.org/observations/36720101 and https://www.inaturalist.org/observations/37716772 and https://www.inaturalist.org/observations/33374342)
• dark bare skin in the anal/perineal area (https://stock.adobe.com/search?k=grysbok&asset_id=418976857 and https://www.inaturalist.org/observations/99380346 and https://en.wikipedia.org/wiki/Sharpe%27s_grysbok#/media/File:Sharpe's_Grysbok_(Raphicerus_sharpei)female(11802609134).jpg)
• a countershaded ventral surface to the torso in R. sharpei (https://www.inaturalist.org/observations/81311519), but not R. melanotis (https://www.inaturalist.org/observations/26439870)
• whitish, transgressing countershading, on the inner surface of the upper hind leg, and on the anterior axil of the fore leg (see https://www.inaturalist.org/journal/milewski/70368-a-new-feature-of-adaptive-colouration-in-ungulates-the-tibial-flag#)
• * slight paleness on the tail, in R. sharpei only (https://www.redbubble.com/people/mags/works/12723988-the-tiny-shy-sharpe-s-grysbok-raphicerus-sharpie and https://www.inaturalist.org/observations/20384185 and https://upload.wikimedia.org/wikipedia/commons/b/bd/Sharpe%27s_Grysbok_%28Raphicerus_sharpei%29_male_%2811838584075%29.jpg

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

• closed: https://www.inaturalist.org/observations/42461838, vs
• open: https://www.inaturalist.org/observations/63753739 and https://www.inaturalist.org/observations/49030465 and https://www.inaturalist.org/observations/127377228 and https://observation.org/photos/9938827/

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

• lacking false hooves (https://www.merriam-webster.com/dictionary/false%20hoof#:~:text=Definition%20of%20false%20hoof,ungulates%20(as%20deer%20and%20pigs)), and
• stamping briefly as it quasi-stots when fleeing (Roberts 1951, Kingdon 2015).

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 el septiembre 23, 2022 09:37 TARDE por milewski