Adaptive radiation of auricular flags in hippotragin bovids: Hippotragus, Oryx, and Addax, part 2

...continued from https://www.inaturalist.org/journal/milewski/88041-adaptive-radiation-of-auricular-flags-in-hippotragin-bovids-hippotragus-oryx-and-addax-part-1#

SUMMARY OF ANTERIOR AURICULAR FLAGS

Species qualifying for an anterior auricular flag are

  • Hippotragus equinus (juveniles),
  • Oryx gazella and Oryx beisa (which share a pattern),
  • Oryx callotis (which differs in pattern from O. beisa), and
  • possibly Addax nasomaculatus (winter pelage).

The clearest depictions so far, of an anterior auricular flag in A. nasomaculatus, are:
https://www.alamy.com/addax-addax-nasomaculatus-hai-bar-reserve-israel-image3637497.html?imageid=81028A0B-4151-454F-A2A3-080D3EED99FB&p=11788&pn=3&searchId=51a17103163bda311280e6d62ad3f212&searchtype=0
https://africageographic.com/stories/critically-endangered-addax-antelope-reintroduced-chad/.
scroll to second photo in https://wildresponse.org/blog/what-species-are-going-extinct/.

DISCUSSION

The bare skin at the centre of the front-of-ear is

This partly reflects an ecological difference, viz. that Hippotragus is more shade- and water-dependent than Oryx. I have yet to see any photo clearly revealing the degree of pigmentation in the case of A. nasomaculatus, in which - paradoxically for a species extremely adapted to desert - the ear pinna does not seem to function as a thermoregulatory panel.

As in my study of dark flank-bands (https://www.inaturalist.org/journal/milewski/87889-surprising-adaptive-radiation-of-the-dark-pigmented-flank-band-in-hippotragin-bovids#), I find O. callotis to be surprisingly different from O. beisa. This suggests that these are different species, not merely subspecies.

The colouration of the ears in hippotragins has radiated, evolutionarily, to the same degree as the facial colouration, but not necessarily in ways congruent with the latter. The emphases only partly correspond.

This evolutionary radiation involves

  • size of ear pinna (largest in H. equinus, smallest in O. dammah)
  • shape of ear pinna (sickle-shaped in H. equinus, narrow in H. niger, O. callotis and A. nasomaculatus, broad in O. gazella, nondescript-oval in O. dammah, O. leucoryx and O. beisa)
  • degree to which the pelage on the front-of-ear opens to shed body heat under thermoregulatory stress (obvious in H. niger, discernible in O. beisa, yet to be detected in A nasomaculatus)
  • apical tufting of ear pinna (only in H. equinus and O. callotis, and individually variable in both spp.)
  • density/length/coverage of pelage on the front-of-ear (hairs long and dense in H. equinus and A. nasomaculatus, short and sparse in most spp. of Oryx, intermediate in O. callotis and H. niger)
  • visible degree of pigmentation of bare skin on front-of-ear (maximal = blackish in Oryx spp., minimal = flesh-coloured in H. niger)
  • pallor (= depigmentation) of pelage on ear pinna (whitish in Hippotragus, A. nasomaculatus, and most spp. of Oryx, medium-tone in O. callotis)
  • apical darkness (without tufting) on ear pinna (absent without trace in O. dammah and O. leucoryx, small in H. niger and some individuals of H. equinus, medium-size in O. beisa and O. gazella)
  • narrow dark outlining of ear pinna (extensive in O. gazella, restricted and hardly noticeable in O. beisa)
  • involvement of base of ear pinna (noticed, so far, only in O. gazella and A. nasomaculatus in winter pelage)
  • exaggeration of size of ear pinna in juveniles (noticeable only in Hippotragus, https://es.123rf.com/photo_121615261_hermosa-cabra-con-grandes-cuernos-se-encuentra-bajo-el-sol.html)
  • sexual dimorphism (pallor on back-of-ear in H. equinus in mature males, see https://www.inaturalist.org/journal/milewski/88277-adaptive-radiation-of-auricular-flags-in-hippotragin-bovids-hippotragus-oryx-and-addax-part-3#).

My impression is that variation among hippotragins in the proportional size of the ear pinnae is adaptive more in terms of signalling (facial expression) than in terms of thermoregulation or acuteness of hearing.

The precociality of the ear in Hippotragus

The dark apical tuft of H. equinus shows

In juveniles, the apical tuft may be as large as the horns (https://www.shutterstock.com/image-photo/roan-antelope-498697057). By contrast, in adolescent males it may wane so completely that not even an apical dark spot remains (https://www.alamy.com/stock-photo-roan-antelope-hippotragus-equinus-adult-w-regional-park-w-transborder-59189738.html?imageid=66386DE1-36D7-4F8B-A3A8-783EC28B2A82&p=86574&pn=5&searchId=5ed1e1ea051df95555f6aaed35fb537c&searchtype=0).

My overall conclusion is as follows.

In hippotragins, the tendency for facial conspicuousness is not paralleled by a commensurate tendency for auricular conspicuousness.

Both the face and the ear pinnae seem maximally conspicuous in O. gazella. However, even in this species, the pale pelage on the front- and back-of-ear do not achieve the whiteness of parts of the face.

What I show in this Post is that an ambivalent conspicuousness of the ears results from a surprising variety (= radiation) of configurations in the various spp. of hippotragins. With respect to the ears, no species could be predicted on the basis of a knowledge of the rest of the species.

This suggests that the ear pinnae and their colouration are finely attuned, adaptively, to the particular habitat and niche of each species.

Hippotragus equinus is perhaps the largest animal on Earth that is specifically adapted to moist/dystrophic savannas, with accordingly modified anatomy, nutrition, physiology, immunology, sociosexual organisation, mutualism with other spp,, etc. Its ears are part of a distinctive syndrome, in ways that remain to be explained.

SUMMARY OF MOST SURPRISING FINDINGS

to be continued in https://www.inaturalist.org/journal/milewski/88277-adaptive-radiation-of-auricular-flags-in-hippotragin-bovids-hippotragus-oryx-and-addax-part-3#...

Posted on January 03, 2024 11:23 PM by milewski milewski

Comments

Please scroll to 11th photo in https://fossilrim.org/blog/what-goes-into-antelope-breeding-decisions/ for the best illustration have yet found of a buccal semet in Connochaetes albojubatus.

Posted by milewski 5 months ago

COLOUR OF BARE SKIN IN HIPPOTRAGUS

The following show that the bare skin on the ear pinna of Hippotragus equinus are flesh-coloured, not pigmented:

https://www.alamy.com/portrait-of-a-male-roan-antelope-hippotragus-equinussouth-africa-image68947753.html?imageid=E479558A-0E2A-47B6-AFC9-D625BC54D2A4&p=3864&pn=1&searchId=d3350f0b953b17636829cec591564ee8&searchtype=0

https://www.alamy.com/stock-photo-head-on-view-of-a-roan-antelope-south-africa-11772234.html?imageid=C332C601-FF66-4140-8EC9-99F85E3F8B18&p=34420&pn=8&searchId=0fe2fe721c9451e6bec5470c488074fe&searchtype=0

https://www.inaturalist.org/observations/173923530

https://www.inaturalist.org/observations/8255165

https://www.alamy.com/stock-photo-roan-antelope-31115637.html?imageid=56CEC700-89E9-457B-AA97-CB80B069338A&p=4877&pn=2&searchId=fc2396d582be6b3410181e7023641baa&searchtype=0

https://www.alamy.com/stock-photo-a-a-rare-roan-antelope-hippotragus-equinus-south-africa-17786559.html?imageid=21A1BF30-6BB1-449C-838D-79823A137F6A&p=30209&pn=7&searchId=48c5019063f87c658c767ebd85f25bc9&searchtype=0

https://www.alamy.com/stock-photo-roan-antelope-hippotragus-equinus-mokala-national-park-south-africa-125537971.html?imageid=A2F7131F-66F6-4C10-84EA-C4EABE9ECA67&p=361664&pn=7&searchId=48c5019063f87c658c767ebd85f25bc9&searchtype=0

https://www.alamy.com/stock-photo-roan-antelope-hippotragus-equinus-female-mokala-national-park-south-125527531.html?imageid=E5C69727-5723-4F55-8E26-5F5B7B2D68F9&p=361664&pn=7&searchId=48c5019063f87c658c767ebd85f25bc9&searchtype=0

Also flesh-coloured are the bare skin of the anus/perineum...

https://www.alamy.com/a-roan-antelope-hippotragus-equinus-in-the-grasslands-of-the-nyika-plateau-nyika-national-park-in-malawi-image344123120.html?imageid=2E70F0EB-F7E4-4352-B0BC-632D6CF4564E&p=1249180&pn=5&searchId=5ed1e1ea051df95555f6aaed35fb537c&searchtype=0

https://www.inaturalist.org/observations/22644312

https://www.inaturalist.org/observations/191344513

https://www.inaturalist.org/observations/164654558

https://www.inaturalist.org/observations/5635964

...and the dorsal surface of the tongue:

https://www.inaturalist.org/observations/5538629

However, the skin on the neck and at the base of the ear pinna seems to be dark-pigmented:

https://www.inaturalist.org/observations/3849930

https://www.inaturalist.org/observations/36255345

The following shows that the bare skin of the anus/perineum is flesh-coloured also in Hippotragus niger:

https://www.alamy.com/stock-photo-black-hippotragues-hippotragus-niger-on-sand-125933105.html?imageid=7E791FF7-2A98-4B26-A0A7-F09E60FF4033&p=263324&pn=11&searchId=846c58e9f060218f95e78ef6508eddfa&searchtype=0

https://www.inaturalist.org/observations/11172391

https://www.alamy.com/in-this-june-20-2018-photo-a-baby-sable-antelope-born-may-13-nuzzles-his-mother-at-the-audubon-species-survival-center-in-new-orleans-about-a-year-after-moving-into-spacious-new-digs-in-new-orleans-african-animals-are-doing-just-what-officials-from-two-zoos-had-hoped-being-fruitful-and-multiplying-ap-photogerald-herbert-image511985143.html

https://www.alamy.com/stock-photo--87142456.html?imageid=C580E98C-814E-42D8-802E-0BB91EC1EB8D&p=20852&pn=7&searchId=2e53d2ed5b881c2af6863ceb6110b704&searchtype=0

For reference:
In Oryx, the anal/perineal bare skin is dark-pigmented:

https://www.alamy.com/close-up-of-a-fringe-eared-oryx-oryx-beisa-callotis-with-long-black-tasseled-tail-muscular-fawn-coloured-body-black-bands-white-muzzle-and-long-c-image261842455.html?imageid=83858366-757A-48AE-84DA-CBB79B414612&p=856738&pn=1&searchId=2acdd3c77239b8025e32abf767a9eb0f&searchtype=0.

Posted by milewski 5 months ago

@matthewinabinett @paradoxornithidae @tonyrebelo @jeremygilmore

The following (https://www.alamy.com/stock-photo-roan-antelope-hippotragus-equinus-seen-in-zimbabwes-hwange-national-136146183.html?imageid=385B0F42-3C40-4AA0-9C22-00752C3F1F4A&p=20852&pn=6&searchId=97540ae770603cf106671452aa5a7a4b&searchtype=0) inadvertently provides a clear comparison between a juvenile and its ostensible mother, in Hippotragus equinus.

This juvenile individual has attained only about half of maternal body mass, and its horns are a mere fraction of the adult length.

However, all of the pelage-adornments (other than, possibly, the tail tassel) are already fully-developed, i.e. adult-size. I refer to the mane, the post-withers mane-tuft, the beard, and the dark apical tufts on the ear pinnae - the last-named being actually larger in juvenile than in adult.

Furthermore, the ear pinna is already as long in juvenile as in adult female.

The bold pattern on the face is already present, albeit not complete.

The following (https://www.alamy.com/roan-antelope-with-foals-hippotragus-equinus-nyika-plateau-malawi-africa-image489313364.html?imageid=B40F7982-6C93-46F8-817F-24328A11A8BD&p=57165&pn=7&searchId=48c5019063f87c658c767ebd85f25bc9&searchtype=0) helps to clarify the degree of precociality of the tail. In the adult female individual, the tip of the tail reaches the hock. In the juvenile individuals, it falls short of the hock. Although the distinction between stalk and tassel is unclear in the adult female, this suggests that the tail tassel is not particularly precocial.

This means that, in terms of precociality, dark apical tuft > mane = post-withers mane-tuft = beard = length of ear pinna > bold facial pattern > tail tassel.

The tail tassel is not an adornment in H. equinus.

This means that, in this species, it is the pelage-adornments that are the most precocial. This seems perverse relative to normal sociosexual expectations.

Posted by milewski 5 months ago

The following (https://www.alamy.com/stock-photo-roan-antelope-hippotragus-equinus-seen-in-zimbabwes-hwange-national-136146190.html?imageid=2F5A245E-39B4-4BED-812C-C2CC09BCE32A&p=20852&pn=6&searchId=97540ae770603cf106671452aa5a7a4b&searchtype=0) shows the difference in overall conspicuousness between Hippotragus equinus and Hippotragus niger. Furthermore, most of the individuals in the group of H. niger are females.

Posted by milewski 5 months ago

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