The three alcelaphin bovids of the Serengeti: a comparison of adaptive colouration, part 1

Dear Reader, please consider the subtle signalling in the following fortuitous comparisons:

https://www.alamy.com/stock-photo-cokes-hartebeest-alcelaphus-buselaphus-cokei-and-topi-damaliscus-lunatus-15876251.html

Scroll to 2nd photo in https://www.thenationalnews.com/lifestyle/travel/circle-of-life-our-guide-to-the-wildebeest-migration-in-kenya-and-tanzania-1.689183

https://www.offset.com/photos/africa-kenya-maasai-mara-national-reserve-young-lion-walking-away-1007049

https://www.agefotostock.com/age/en/details-photo/topi-left-watched-by-a-kongoni-coke-s-hartebeest-which-is-a-sub-species-of-the-red-hartebeest-serengeti-tanzania/RHA-1161-186

In the Serengeti ecosystem, there are three coexisting genera and species of alcelaphin bovids (https://inaturalist.nz/taxa/846320-Alcelaphini), viz.

• Connochaetes mearnsi (see https://www.inaturalist.org/journal/milewski/54094-adaptive-colouration-in-wildebeests-part-1-an-introduction-to-large-scale-conspicuous-features#),
• Damaliscus jimela (see https://www.inaturalist.org/journal/milewski/77351-subtle-differences-between-the-tsessebe-southern-africa-and-the-topi-east-africa#), and
• Alcelaphus cokii (https://www.inaturalist.org/observations/28485278).

Furthermore, all are of similar body mass, viz. about 100-200 kg.

This raises the question of the ecological diversification that allows their coexistence. How do the three species differ in their signalling, both socially and in communication with predators?

In this Post, I focus on the similarities and differences among these three, in adaptive colouration.

In particular, I recognise certain themes and patterns of conspicuous colouration, illustrating their incidence in C. mearnsi, D. jimela, and A. cokii.

What complicates this exercise is that alcelaphin bovids are extreme, among all the ruminants of the world, in their development of

• sheen/anti-sheen, and
• brindling (https://en.wikipedia.org/wiki/Brindle).

SHEEN

Sheen - which produces a non-pigmentational pale effect according to illumination - is an important theme in all three species (https://www.inaturalist.org/observations/70079036).

However, its most important effects differ in anatomical location, as follows:

• rump/back, i.e. dorsal emphasis, in C. mearnsi,
• buttocks and rump in D. jimela, and
• buttocks in A. cokii.

ANTI-SHEEN

A converse theme is anti-sheen, which produces a non-pigmentational dark effect according to illumination.

This is

• most important in C. mearnsi (in which it is the dominant aspect of the overall colouration, https://bpb-us-w2.wpmucdn.com/blogs.socsd.org/dist/f/44/files/2011/10/Copy-of-P1000514.jpg), and
• least important in A. cokii (in which the figure virtually never looks conspicuously dark).

LACK OF COUNTERSHADING ON TORSO

Related to anti-sheen is another theme, viz. the lack of countershading on the torso. The combination of pigmentation and shading means that the ventral silhouette is underscored, making the whole figure conspicuous.

This is nicely illustrated in https://www.inaturalist.org/observations/150562001. The inner surfaces of the upper legs are somewhat depigmented, as expected according to the principle of countershading. However, there is no such depigmentation on the normally shaded ventral surface of the thorax and abdomen.

(Incidentally, this photo also nicely shows that the beard of C. mearnsi is not consistently pale enough to be conspicuous.)

Of the three species of alcelaphins in the Serengeti, it is A. cokii that shows this theme least clearly. However, it does seem to apply even in this species (https://www.gettyimages.co.uk/detail/photo/male-hartebeest-standing-on-field-ololosokwan-royalty-free-image/1342077720?phrase=kongoni&adppopup=true and https://www.shutterstock.com/it/image-photo/red-hartebeest-walks-across-brown-grass-2220959159 and https://www.inaturalist.org/observations/34843838).

In the following illumination, A. cokii seems at first to show no conspicuous features of colouration (https://www.inaturalist.org/observations/31957048). However, please note that the lack of countershading on the torso does make the figure stand out from the background to some degree.

Supporting this interpretation is that infants of A. cokii possess countershading that is lost in adulthood (https://www.alamy.com/stock-photo-mother-and-baby-hartebeest-alcelaphus-buselaphus-cokes-race-standing-41586065.html?imageid=97FFCDA1-E76D-4DC9-A494-16FAF35E605A&p=39374&pn=1&searchId=6cb6d804e8c2d0cca41f0eed698c3a54&searchtype=0).

Along similar lines, the following show that, in D. jimela, infants differ from adults in possessing countershading (https://www.alamy.com/a-female-topi-damaliscus-lunatus-jimela-followed-by-her-calf-runs-through-dry-grass-serengeti-national-park-tanzania-image336476496.html?imageid=0C711FFD-C359-4129-95FF-76DD226BC931&p=39397&pn=1&searchId=70a63ba4e73d117d4dc267df2c6a9d78&searchtype=0 and https://www.alamy.com/newborn-korrigum-topi-damaliscus-lunatus-korrigum-playing-after-the-rains-masai-mara-game-reserve-kenya-december-image263058037.html?imageid=C4C0FAE6-5E56-4313-9E12-EE16A9882121&p=269351&pn=1&searchId=6cb6d804e8c2d0cca41f0eed698c3a54&searchtype=0).

The following shows that countershading in D. jimela persists to a juvenile stage when the adult markings on shoulders and haunches have already started to appear (https://www.inaturalist.org/observations/27634388).

BRINDLING

See https://www.dreamstime.com/wildebeest-wildebai-also-called-gnu-antelope-genus-connochaetes-hooved-ungulate-mammal-skin-image190267038 and https://www.dreamstime.com/wildebeest-wildebai-also-called-gnu-antelope-genus-connochaetes-hooved-ungulate-mammal-skin-image190267061.

As a theme, brindling is not categorically different from anti-sheen, together with which it is particularly well-developed in alcelaphin bovids.

Brindling is well-developed in C. mearnsi (https://upload.wikimedia.org/wikipedia/commons/f/fb/Blue_Wildebeest%2C_Ngorongoro.jpg), and poorly-developed but present in the other two species.

The following show the maximum brindling in

• D. jimela (https://www.inaturalist.org/observations/120960354), and
• A. cokii (https://www.shutterstock.com/image-photo/topi-antelope-maasai-mara-national-reserve-1846801051).

Having covered the themes, let us focus on the patterns.

PYGAL AND ISCHIAL FLAGS

All three species of alcelaphins in the Serengeti show conspicuous pale on the hindquarters.

In all of them, this is based mainly on sheen.

However, the species differ

• in the anatomical location of the sheeniest surfaces, and
• the contribution to pallor by depigmentation of the pelage.

The contribution to conspicuousness of the hindquarters by depigmentation is

• least in C. mearnsi, in which the effect is entirely sheen-based, and
• most in A. cokii (https://www.shutterstock.com/it/image-photo/two-coke-hartebeest-stand-on-grassy-1717314901).

The pale feature in the hindquarters is centred on the rump in C. mearnsi, and on the buttocks in D. jimela and A. cokii (https://www.agefotostock.com/age/en/details-photo/topi-left-watched-by-a-kongoni-coke-s-hartebeest-which-is-a-sub-species-of-the-red-hartebeest-serengeti-tanzania/RHA-1161-186 and https://www.inaturalist.org/observations/149771685).

'Pygal' refers to the rump, whereas 'ischial' refers to the buttocks.

The following show the pygal/ischial flags of the three species at their most conspicuous:

• pygal flag in C. mearnsi (https://www.inaturalist.org/observations/139835345 and https://www.inaturalist.org/observations/134466267)
• ischial and possibly also pygal flag in D. jimela (https://www.alamy.com/line-up-of-three-alert-female-topi-damaliscus-lunatus-jimela-watching-predator-on-the-plains-of-the-maasai-mara-conservancies-kenya-africa-image178826795.html?imageid=1EA5E806-C021-4612-929F-6BE31315C64D&p=38682&pn=1&searchId=70a63ba4e73d117d4dc267df2c6a9d78&searchtype=0 and https://www.alamy.com/stock-photo-topi-damaliscus-lunatus-also-known-as-tsessebe-in-kenyas-masai-mara-12361353.html?imageid=C2951267-B9D2-4840-9D92-BF41A795AAF8&p=3616&pn=16&searchId=e1dc7e88d3225c439fd56c16145d0d60&searchtype=0 and https://stock.adobe.com/search?k=%22topi+antelope%22&asset_id=327349586 and https://stock.adobe.com/search?k=%22common+tsessebe%22&asset_id=36110686)
• ischial flag in A. cokii (https://www.inaturalist.org/observations/132603725).

The following shows that, in C. mearnsi, the pygal flag arises from the combination of sheen on the rump and anti-sheen on the flanks and haunches (https://www.inaturalist.org/observations/151760045).

Such an effect is rarely seen in A. cokii, but the following does show contrast arising from sheen on the hindquarters vs antisheen on the back (https://www.inaturalist.org/observations/14374050 and https://stock.adobe.com/search?k=%22topi+antelope%22&asset_id=343177249).

The following shows that, even in A. cokii, sheen can occur on the dorsal surface of the rump (https://www.inaturalist.org/observations/35809197). However, this appears too infrequently to qualify as a pygal flag.

In the following views (https://www.agefotostock.com/age/en/details-photo/coke-s-hartebeest-kongoni-alcelaphus-buselaphus-cokii-three-adults-running-in-savanna-serengeti-national-park-tanzania/SSJ-179781 and https://www.inaturalist.org/observations/19944808), the ischial flag is clearly expressed in one of the individuals. This may perhaps be a matter of individual variation. However, I suspect that it is, instead, a matter of sheen.

The following show that the pygal and ischial flags are absent in infants:

• C. mearnsi (https://www.dreamstime.com/stock-photo-great-migration-wildebeests-serengeti-image8420550)
• D. jimela ()

In A. cokii, a previously overlooked difference between infants and adults is that the pelage on the uppermost, innermost buttocks is fully depigmented in the former (https://www.alamy.com/cokes-hartebeest-alcelaphus-bucephalus-cokii-mother-and-young-masai-mara-game-reserve-kenya-image262961718.html?imageid=AB2B3BD6-2B1C-4A59-B45C-A24DEEAA1D0E&p=269351&pn=1&searchId=6cb6d804e8c2d0cca41f0eed698c3a54&searchtype=0 and https://www.inaturalist.org/observations/142342276).

ULNAR FLAGS

Ulnar flags are

• absent in C. mearnsi,
• arguably present in D. jimela (https://www.inaturalist.org/observations/106859165 and https://www.inaturalist.org/observations/103750347), and
• absent in A. cokii, but with qualifications.

In D. jimela, the dark pelage on the upper foreleg tends to be darker than that on the upper hindleg, as well as that on the shoulders and haunches. The medium-tone pelage on the posterior surface of the upper foreleg may not be depigmented enough to provide the degree of dark/pale contrast for qualification as a flag. However, sufficient contrast may be achieved by means of sheen.

The following show the pattern most clearly (https://www.alamy.com/stock-image-kenya-topi-damaliscus-korrigum-standing-on-termite-mound-168773190.html?imageid=4A93A0DB-DC87-4780-A5A1-93D04B9B231D&p=570783&pn=16&searchId=e1dc7e88d3225c439fd56c16145d0d60&searchtype=0 and https://www.alamy.com/stock-photo-kenya-masai-mara-topi-damaliscus-lunatus-side-view-15328201.html?imageid=600969F7-278E-4FAA-AE27-A65385DDE5FA&p=50040&pn=15&searchId=a0557c0a3d4c017133cb83a5f01cb6a7&searchtype=0).

Please see https://www.inaturalist.org/observations/35622892 and https://www.inaturalist.org/observations/32009259 and https://www.inaturalist.org/observations/36514600.

In these typical views, the dark on the ulnar surface is intense, that on the hindleg tends to be dissipated by sheen. However, at the same time, the other tone on the ulnar surface remains darker than the pale of the lowermost buttocks.

As a result, dark/pale contrast generally falls short of conspicuousness on both fore and hind surfaces, in different ways. It thus remains ambivalent whether D. jimela qualifies for an ulnar flag or not.

In A. cokii, there is no pattern on the posterior surface of the upper foreleg (https://www.shutterstock.com/it/image-photo/closeup-cokes-hartebeest-scientific-name-connochaetes-772737676 and https://www.shutterstock.com/it/image-photo/hartebeest-maasai-mara-kenya-1896708001).

However, this surface is depigmented enough that, when sheen applies, it can - together with the posterior surfaces of the legs generally - be whitish (https://www.agefotostock.com/age/en/details-photo/red-hartebeest-alcelaphus-buselaphus-serengeti-national-park-tanzania/C64-333509 and https://www.shutterstock.com/it/image-photo/hartebeest-family-nairobi-national-park-2260126749 and https://www.shutterstock.com/it/image-photo/young-hartebeest-leaves-mother-sunlit-savannah-1730346106).

This pallor in A. cokii is poorly explained by the principle of cryptic countershading. Instead, it seems to serve as a conspicuous feature, complementing and extending the ischial flag when viewed in posteriolateral perspective.

FACIAL FLAGS

Facial flags are at best nebulous in adults of the alcelaphin bovids of the Serengeti.

In adults of C. mearnsi, the beard is sometimes conspicuous, particularly when backlit (https://www.gettyimages.ae/detail/video/the-wildebeest-and-its-baby-walking-in-serengeti-stock-video-footage/1089966386?adppopup=true and https://www.gettyimages.ae/detail/video/the-wildebeest-and-its-baby-walking-in-serengeti-stock-video-footage/1089962972?adppopup=true).

However, this is inconsistent, with most photos showing the beard as inconspicuous (https://www.alamy.com/stock-photo-wildebeests-56489832.html?imageid=BE92527C-4766-4A07-AFEA-277226D22E9E&p=180380&pn=4&searchId=e495fe81b41c4ac2a2aa1b51980ecf14&searchtype=0 and https://www.dreamstime.com/isolated-wildebeest-walking-savannah-single-short-green-grass-maasai-mara-image207464059 and https://www.dreamstime.com/portrait-as-lone-female-wildebeest-side-walking-grasslands-maasai-mara-image207464226).

The following hunts at a facial flag in adults of C. mearnsi, in frontal view (https://www.shutterstock.com/it/image-photo/close-whitebearded-wildebeest-standing-facing-camera-1059264716).

In infants of C. mearnsi, the face is precocially dark, to a degree unknown in the genera Damaliscus and Alcelaphus.

Furthermore, this frontal darkness contrasts with the paleness of the cheek, to a degree not seen in adults of C. mearnsi (https://www.shutterstock.com/it/image-photo/adult-wildebeest-stands-beside-recently-born-1277282221 and https://www.kimballstock.com/preview.asp?db=a&image=AFW+03+MC0026+01 and https://www.alamy.com/side-profile-of-a-wildebeest-and-its-calf-running-in-a-field-ngorongoro-conservation-area-arusha-region-tanzania-image376769166.html?imageid=6A76B279-D007-4009-9AC4-A3AC8F486DC9&p=1132882&pn=1&searchId=7a9d75e9925e3ea8c217697d70b14364&searchtype=0 and https://www.alamy.com/blue-wildebeest-connochaetes-taurinus-mother-with-newborn-calf-running-at-the-southern-plains-during-the-migration-ngorongoro-conservation-area-t-image226468917.html?imageid=4C5F3612-7996-4AAE-B872-BFEFE733DB9C&p=157727&pn=1&searchId=7a9d75e9925e3ea8c217697d70b14364&searchtype=0 and https://www.alamy.com/newborn-calf-running-between-two-adult-wildebeest-lake-ndutu-tanzania-image246936718.html?imageid=FAB728C2-9CFF-4B0D-8019-7F4B934A0F60&p=184594&pn=1&searchId=7a9d75e9925e3ea8c217697d70b14364&searchtype=0 and https://www.alamy.com/stock-photo-blue-wildebeest-connochaetes-taurinus-mother-and-1-to-3-days-old-calf-125592011.html?imageid=5FC5A052-2DF2-4534-B1F8-7B839EC77DB8&p=361867&pn=1&searchId=7a9d75e9925e3ea8c217697d70b14364&searchtype=0).

Connochaetes mearnsi thus seem to qualify for a facial flag in the infantile colouration. This is extremely odd among ruminants, in which infants are usually inconspicuous.

In adults of D. jimela, the face is dark but lacks pale contrast, apart from the pale on the anterior of the ear pinnae.

In A. cokii, there is no facial flag. The darkest appearance of the front of the face falls well short of conspicuousness (https://www.inaturalist.org/observations/8655787 and https://www.inaturalist.org/observations/30264495).

To be continued in https://www.inaturalist.org/journal/milewski/77617-the-three-alcelaphin-bovids-of-the-serengeti-a-comparison-of-adaptive-colouration-part-2#...

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 abril 5, 2023 07:47 TARDE por milewski