Three patterns of colouration in one species: the ontogenetic 'triplexity' of the blesbok/bontebok (Damaliscus pygargus)

@errol-d

At first glance, the most remarkable aspect of the colouration of the blesbok/bontebok (Damaliscus pygargus) is the whitish rostrum, which constitutes a facial bleeze.

The bold, pale feature on the face of this species is extreme among all of the ungulates. This is because

However, on closer scrutiny, what may be more remarkable is that D. pygargus features three different patterns of colouration within each individual - following each other from birth to adulthood.

Another way of putting this is that infants, juveniles, and adults of D. pygargus have such different colouration that they are like three different species in one.

The main aim of this Post is to illustrate this 'triplex' colouration by means of a few, carefully selected photos.

CRYPTIC COLOURATION

Within D. pygargus, something approaching a classic example of cryptic colouration occurs: plain fawn with countershading.

This occurs from birth to three months old, after which it changes abruptly. Thus, the 'infantile' colouration lasts until weaning begins.

The cryptic 'infantile' pattern makes little sense adaptively, because there is no rationale for inconspicuousness in this species, even in infants.

Blesbok infants https://www.robertharding.com/preview/741-3687/blesbok-damaliscus-dorcas-kariega-game-reserve-south-africa/ and https://www.zooborns.com/zooborns/2018/08/meet-betty-bantu-belfasts-blesbok-calf.html

Bontebok infants https://www.shutterstock.com/it/image-photo/cute-baby-bontebok-antelope-calf-looks-744728965

DARK FACE CONTRASTING WITH PALE CHEEKS

For the next three months, when the freshly-weaned juveniles weigh about half as much as their mothers, the pattern on the face differs from those of both infants and adults. This facial pattern is

Supporting the interpretation that this constitutes a frontal display is the fact that the upper forelegs darken, precocially, at this stage.

The frontal conspicuousness of juveniles makes little sense adaptively. This is because there is no rationale for adults and accompanying juveniles achieving such conspicuousness in different ways.

Blesbok juveniles https://www.alamy.com/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-image65490812.html?imageid=E925F6B0-7DB8-4381-90A4-A1DB36C2A783&p=94604&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0 and https://www.alamy.com/juvenile-blesbok-damaliscus-pygargus-phillipsi-mountain-zebra-national-image65490807.html?imageid=B8EA5253-B43F-41C0-8B90-B1BD0FE8E257&p=94604&pn=1&searchId=34a5985d254a7cecee5d7188055b6b4c&searchtype=0https://www.gettyimages.no/detail/photo/blesbok-antelope-royalty-free-image/95006564?adppopup=true

Bontebok juveniles https://www.alamy.com/stock-photo-herd-of-bontebok-antelope-with-calf-23274728.html?imageid=B8F63BA8-FA72-44CE-80AC-2EF5979BF4BB&p=71732&pn=1&searchId=abde0ec3b06a08943ffb523ff66f0db0&searchtype=0

CONSPICUOUSLY PALE FACE

Gradually and with individual variation, the rostrum turns from dark to pale, and the cheeks turn from pale to dark. The pale tends to creep upwards from the nose towards the eyes.

The conspicuous colouration of adults of D. pygargus makes sense, in principle. This is because gregarious, cursorial ungulates of open environments have nowhere to hide from predators, and have much to gain from social cohesion. However...

Blesbok adult https://stock.adobe.com/search/images?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&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=blesbok&order=relevance&price%5B%24%5D=1&safe_search=1&limit=100&search_page=3&search_type=pagination&get_facets=0&asset_id=495936526 and https://www.istockphoto.com/photo/blesbok-antelope-gm144341776-4192140?phrase=pics%20of%20a%20blesbok

Bontebok adult https://www.alamy.com/bontebok-in-the-bontebok-national-park-swellendam-western-cape-south-africa-image342638387.html?imageid=5C55BBE5-4514-4B34-AEDA-ACC05175FD68&p=22337&pn=1&searchId=b907bfe35d3c66fdb917f996c60ff601&searchtype=0

DISCUSSION

The 'triplexity' of colouration in D. pygargus remains to be explained, in adaptive terms.

Also remaining unexplained, in D. pygargus, are why

  • this species exceeds other members of the same genus in conspicuous colouration,
  • the face is the location of particular conspicuousness,
  • in adults, the bontebok greatly exceeds the blesbok in the conspicuousness of the colouration, and
  • in infants and juveniles, the blesbok somewhat exceeds the bontebok in the conspicuousness of the colouration.

Also see:
https://www.inaturalist.org/journal/milewski/76599-the-mystery-of-the-adaptive-value-of-cryptic-colouration-for-the-first-three-months-of-life-in-the-bontebok#
https://www.inaturalist.org/journal/milewski/76550-a-concise-photo-guide-to-the-differences-some-previously-overlooked-between-blesbok-and-bontebok#
https://www.inaturalist.org/journal/milewski/75748-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-1-adults#
https://www.inaturalist.org/journal/milewski/75995-adaptive-colouration-in-the-blesbok-damaliscus-pygargus-phillipsi-part-2-infants-juveniles-and-adolescents#
https://www.inaturalist.org/journal/milewski/76311-adaptive-colouration-in-the-bontebok-damaliscus-pygargus-pygargus-part-1-adults#
https://www.inaturalist.org/journal/milewski/76336-adaptive-colouration-in-the-bontebok-damaliscus-pygargus-pygargus-part-2-infants-juveniles-and-adolescents#

For an index to my many Posts about the genus Damaliscus, please see https://www.inaturalist.org/journal/milewski/78238-an-index-to-my-posts-on-genus-damaliscus#.

Publicado el marzo 22, 2023 10:52 TARDE por milewski milewski

Comentarios

Here are two remarkable illustrations of the blesbok:

https://www.inaturalist.org/observations/152116379

Publicado por milewski hace 11 meses

Furstenburg and Currie (2019), on Damaliscus pygargus pygargus:

https://www.hrpub.org/download/20191230/EER2-14014302.pdf

Publicado por milewski hace 11 meses

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