Glandular contrasts between Aepyceros (impalas) of Africa and Odocoileus (white-tailed, black-tailed, and mule deer) of the Americas

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Also please see https://www.inaturalist.org/posts/53455-the-white-tailed-deer-has-more-than-just-a-caudal-flag#

The bovid genus Aepyceros (https://www.inaturalist.org/observations?taxon_id=42277) and the cervid genus Odocoileus (https://www.inaturalist.org/observations?taxon_id=42219) are biologically comparable.

The former (https://en.wikipedia.org/wiki/Aepyceros) tends to be the most abundant ruminant in its habitat in southern and East Africa. The latter is the only ruminant of similar body size, shape, and colouration in much of North, central, and South America (https://en.wikipedia.org/wiki/Odocoileus).

In this Post, I compare the various externally-expressed glandular organs (https://en.wikipedia.org/wiki/Scent_gland) in the two genera, in anatomical order from anterior to posterior.

NASAL GLANDS

A nasal gland is present in Odocoileus (https://www.jstor.org/stable/1381763), but unrecorded in Aepyceros.

This corresponds to the fact that the rhinarium - and particularly its moist surface - is far smaller in Aepyceros (https://upload.wikimedia.org/wikipedia/commons/6/6b/Female_impala_headshot.jpg) than in Odocoileus (https://www.istockphoto.com/photo/a-portrait-of-a-female-whitetail-deer-in-the-wild-pennsylvania-poconos-usa-gm1480690655-508276186?searchscope=image%2Cfilm and https://www.istockphoto.com/photo/deer-face-portrait-gm1157065175-315582928?searchscope=image%2Cfilm).

The functions of the secretions of the nasal gland probably include facilitation of vomeronasal olfaction (https://en.wikipedia.org/wiki/Vomeronasal_organ).

Both Aepyceros and Odocoileus use the vomeronasal organ in the flehmen response (https://en.wikipedia.org/wiki/Flehmen_response and https://www.naturepl.com/stock-photo-nature-image01614388.html and https://www.alamy.com/stock-photo-white-tailed-buck-24107401.html?imageid=B11DA485-3888-42C5-AA88-CFD56C190728&p=50996&pn=1&searchId=b440fe464398d3b141934cb8e39734c0&searchtype=0 and https://www.alamy.com/stock-photo-white-tailed-buck-performing-flehmen-24198454.html?imageid=6972F032-0CA4-4D7E-B28F-3ACCE89ED655&p=50996&pn=1&searchId=b440fe464398d3b141934cb8e39734c0&searchtype=0).

However, the American genus may, in addition, have a broad vomeronasal olfactory facilitation, lacking in the African genus.

In both genera, there is an uninvestigated possibility of pheromonal/scent-production by nasal glands, spread by alarm-sneezing/snorting.

PREORBITAL GLANDS (https://en.wikipedia.org/wiki/Preorbital_gland)

Both Aepyceros and Odocoileus are unusual among ruminants, in that preorbital glands are absent/poorly-developed.

Their only incidence is in adult males of Odocoileus in rutting condition. They have a masculine function in olfactory marking of plant stems/foliage, in combination with the licking of these objects (https://issuu.com/texaswildlifeassociation/docs/2022-11-november_texas_wildlife/s/17179654).

SALIVARY GLANDS

The main function of salivary glands is in eating. However, there is a possibility of olfactory communication, by means of active or passive protrusion of the tongue.

Both genera show passive lingual protrusion (https://www.inaturalist.org/journal/milewski/90191-the-puzzle-of-passive-lingual-protrusion-in-ruminants-part-3-explanation-via-a-new-hypothesis# and https://www.shutterstock.com/image-photo/doe-raspberry-tongue-mule-deer-high-1570312519). However, only Odocoileus uses the tongue for social licking/grooming.

FRONTAL GLANDS

In adult males of both Aepyceros and Odocoileus, masculine olfactory marking of vegetation is carried out by rubbing the pelage of the forehead on plants.

INTERDIGITAL GLANDS

Aepyceros is unusual among both bovids and cervids in lacking interdigital glands, as well as having feet so specialised that dewclaws/false hooves are absent.

Odocoileus possesses interdigital glands on both fore- and hindlegs.

Furthermore, the American genus is somewhat unusual in that it exhibits demonstrative postures/gaits, which potentially promote and advertise the emission of interdigital secretions in an anti-predator context. I refer to stotting in Odocoileus hemionus hemionus and 'foot-stamping' in Odocoileus virginianus.

PREPUTIAL GLANDS

Preputial glands are absent in Aepyceros, but present in mature males of Odocoileus.

TARSAL GLANDS

Please see the pale patch on the inner surface of the hock (https://en.wikipedia.org/wiki/Hock_(anatomy)) in https://www.alamy.de/stockfoto-white-tailed-doe-ausgefuhrt-23483768.html?imageid=EDACD125-8C59-4F3A-A9DC-81CC5DE6257C&p=50996&pn=12&searchId=b5f000b2ab7925e33bdd76e9f2b7a8b9&searchtype=0, which shows an adult female individual of Odocoileus virginianus in summer pelage.

Tarsal glands are unrecorded in bovids, including Aepyceros.

https://en.wikipedia.org/wiki/(Z)-6-Dodecen-4-olide

The tarsal gland in Odocoileus is a feature of the pelage rather than a gland. It functions

to culture microbes intensively, based partly on the urine that is dribbled on to it by means of special squatting postures, and thus
to function mainly socially, producing olfactory signatures distinctive individually and according to sex, age, condition, and status.

METATARSAL GLANDS

Please see

just above the hind fetlock in https://www.alamy.com/video/close-up-scent-glands-on-impala-hind-leg-black-tuft-tilt-up-striped-buttocks-419797686.html, and
the pale spot on the outer surface of the lower hindleg in https://www.alamy.de/stockfoto-white-tailed-doe-lauft-in-eine-sommerwiese-23502407.html?imageid=E259A279-267B-448E-B4D5-F96EE0B555E4&p=50996&pn=12&searchId=b5f000b2ab7925e33bdd76e9f2b7a8b9&searchtype=0, which shows an adult female individual of Odocoileus virginianus in summer pelage.

Metatarsal glands occur in certain cervids, but are unrecorded in bovids other than Aepyceros.

Their function seems to be specialised: they react to anti-predator alarm by releasing olfactory signals, presumably detectable to both other members of the group and the predators themselves.

In the case of Odocoileus hemionus columbianus, the garlic-like odour of alarm is perceptible to humans.

The metatarsal glands in Aepyceros and Odocoileus are similar in anatomical position, on the lower hindlegs. However, they differ in that, in Aepyceros,

the accompanying tufts, situated close to the fetlocks, are large and dark-pigmented (https://www.shutterstock.com/image-photo/metatarsal-glands-on-impalas-back-legs-2337218443 and https://www.shutterstock.com/image-photo/impala-hind-legs-air-while-running-2091648148 and https://www.dreamstime.com/female-common-impala-throws-up-rear-legs-female-common-impala-throws-up-rear-legs-image205814034), and
there is a pair with bilateral symmetry (https://www.dreamstime.com/stock-photo-impala-legs-mkuze-national-park-south-africa-image54790604 and https://www.alamy.com/impala-aepyceros-melampus-rump-markings-leg-hock-ankle-fetlocks-associated-swollen-black-glands-cloven-hoof-hooves-female-animal-walking-image398733683.html), as opposed to the restriction in Odocoileus to a single feature on the outer surface of the metatarsus.

Within Odocoileus, there is noteworthy variation in the degree of development of the metatarsal gland both between and within species. The gland is better-developed in O. hemionus than in O. virginianus, and within the latter species it tends to be absent in the tropics and subtropics.

CAUDAL GLANDS

Caudal glands are unrecorded, and presumably absent, in Aepyceros, in line with most bovids.

However, caudal glands are known in Odocoileus.

As in the case of metatarsal glands, caudal glands are better-developed in O. hemionus than in O. virginianus. They presumably function mainly in anti-predator alarm.

VARIOUS SOURCES OF INFORMATION

https://animaldiversity.org/accounts/Odocoileus_hemionus/

https://heatedhunts.com/deer-scent/deer-glands/

https://keepingtrack.org/sites/default/files/uploads/92_Whitetail_GETTING%20TO%20THE%20BOTTOM%20OF%20WHITETAIL%20SCRAPES.pdf

https://deerassociation.com/tarsal-glands-know/

https://woods-n-waternews.com/2010/06/01/articles-i-2010-06-01-205048-112113-the-role-of-skin-glands-in-deer-odor-communication-html/

https://www.fieldandstream.com/articles/hunting/2009/11/how-whitetail-glands-work/

https://deerassociation.com/meet-the-7-glands-of-the-whitetail-and-a-bonus-organ/

https://www.bowhunting.com/bowhunt101/7-whitetail-deer-glands-and-what-they-do/

https://www.mossyoak.com/our-obsession/blogs/deer/scent-glands-101-making-sense-of-whitetails-scent-glands

https://www.huntstand.com/fieldnotes/deer/body-language-how-whitetails-talk-with-their-glands/

https://www.youtube.com/watch?app=desktop&v=JT8sKU5cm-k

https://link.springer.com/article/10.1007/BF00987357

https://eprints.soton.ac.uk/459805/

https://www.cambridge.org/core/journals/journal-of-zoology/article/abs/individual-signatures-in-scent-gland-secretions-of-eurasian-deer/E5E1D0438C87B8981C82D714D72B3335

DISCUSSION

Overall, the glandular profiles of Aepyceros and Odocoileus are surprisingly different, in ways unexplained by the fact that Aepyceros is sociosexually territorial, whereas Odocoileus is not.

The main similarities are

masculine sebaceous function in the pelage of the forehead, and
metatarsal glands, ostensibly functioning to signal anti-predator alarm, particularly during bounding/kick-stotting/stotting.

Aepyceros is poor in glands generally, and is extreme in lacking interdigital glands, a category common to various ruminants. For its part, Odocoileus is extreme in the degree of development of its tarsal glands, a category absent from all bovids.

Females of Aepyceros have only one important type of gland, viz. the metatarsal gland, and even this is thought not to be used sociosexually.

Compared to other bovids, Aepyceros communicates unusually raucously (https://www.inaturalist.org/journal/milewski/90798-auditory-communication-in-impalas-aepyceros-alarm-calls-masculine-calls-and-confusion-between-the-two#).

This auditory emphasis may perhaps partly explain the limited olfactory communication in Aepyceros.

The glandular differences shown above may also be partly related to the remarkable disparities in gaits and postures between the two genera (https://www.inaturalist.org/posts/67632-locomotory-and-postural-peculiarities-of-the-impala-part-2#).

These differences are greatest between the common impala (Aepyceros melampus) and the Rocky Mountain mule deer (O. hemionus hemionus, https://www.inaturalist.org/taxa/143865-Odocoileus-hemionus-hemionus), as follows.

The common impala

By contrast, the mule deer

Furthermore,

the common impala never forages bipedally, seldom lies down (sternally recumbent) in adulthood during daylight, does not deliberately jump fences, and swims poorly (https://www.youtube.com/watch?v=mq9SMyWC3gQ), whereas
the mule deer sometimes forages bipedally, often lies down during daylight (https://www.shutterstock.com/image-photo/female-mule-deer-high-grass-calgary-1199493106), readily jumps fences (https://www.instagram.com/bandeliernps/p/C1mrcqbvYIM/ and https://www.istockphoto.com/photo/stag-deer-starting-his-jump-over-fence-gm1287699187-383842921?phrase=deer+running+animal+blurred+motion&searchscope=image%2Cfilm), and swims well (https://www.youtube.com/watch?v=MjOxw0gnuYM and https://www.youtube.com/watch?v=WzE2MmxmnFs and https://www.youtube.com/watch?v=iCYtR8VdkPo and https://www.youtube.com/watch?v=HX7svF1Kii4 and https://www.youtube.com/watch?v=MjOxw0gnuYM and https://kids.gwnews.com/news-shorts/deer-rescue).

Also see https://www.inaturalist.org/journal/milewski/39738-contrary-to-field-guide-books-reedbucks-redunca-spp-do-not-flag-the-tail-in-alarm#

Posted on March 9, 2024 03:24 PM by

milewski

Glandular contrasts between Aepyceros (impalas) of Africa and Odocoileus (white-tailed, black-tailed, and mule deer) of the Americas

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