Adaptive colouration in the oribi: southern forms are more conspicuous than northern forms

Ourebia ourebi is widespread in African savannas (https://animalia.bio/oribi and http://elelur.com/data_images/mammals/oribi/oribi-03.jpg and https://parody.fandom.com/wiki/Oribi?file=Oribi.jpg and https://www.youtube.com/watch?v=kDq-rtTFUyM and https://kenyacradle.com/oribi-antelope-in-kenya/ and https://www.researchgate.net/profile/Brenda-Daly/publication/282183812_Oribi_antelope_Ourebia_ourebi_population_and_habitat_viability_assessment/links/560685af08ae5e8e3f346be0/Oribi-antelope-Ourebia-ourebi-population-and-habitat-viability-assessment.pdf).

The subspecies of O. ourebi (https://africatrophyhunting.com/plains-category/oribi-southern-africa/) remain putative, and unconfirmed by taxonomists.

However, at first sight it would seem that these various forms of Ourebia are of trivial importance, beyond the usual geographical variation, seen in any widespread species.

The aim of this Post is to show that there is a geographical pattern in the adaptive colouration of the species, with the southern African sspp. more conspicuous than those in eastern, north-central, and West Africa.

The basis of my argument is as follows.

In O. ourebi in general, the colouration is inconspicuous, overall (https://www.inaturalist.org/observations/38422719).

This makes sense for a small-bodied antelope, living mainly in monogamous pairs, in grassland tall enough to provide some cover, at least while the animals are lying down.

The particular type of inconspicuous colouration, seen in O. ourebi, is crypsis (https://en.wikipedia.org/wiki/Crypsis).

This means that the pale underparts serve as countershading, and there are no dark/pale contrasts of sufficient scale to draw attention to the figure, at the ranges relevant to scanning by predators.

However, the following view (https://www.inaturalist.org/observations/67132059) shows that the colouration of O. oribi can have an extremely conspicuous aspect.

Ourebia ourebi tends to be diurnally active, suggesting that its strategy is not simply furtive.

Furthermore, it differs from most other bambis (https://www.inaturalist.org/posts/53647-the-bambis-part-1-introduction-to-the-category-of-diminutive-ruminants) in stotting (https://en.wikipedia.org/wiki/Stotting) when alarmed by the approach of potential predators.

This is a form of self-advertisement by means of an exuberant gait, somewhat accentuated by a certain pattern of dark/pale contrast on and near the tail. The tail is usually raised and wagged during running (including stotting), which is unlike most other small antilopin bovids.

The following (https://www.gesser-images.com/imagebank/africa/other-mammals/bohor-reedbuck/bohor-reedbuck-002-_dm31049/) shows stotting in O. ourebi cottoni, here mislabelled as Redunca.

The following (https://www.gesser-images.com/imagebank/africa/other-mammals/bohor-reedbuck/bohor-reedbuck-001-_dm31043/) shows the same individual, standing in alarm.

What I have noticed is that two southern sspp. of O. ourebi have pelage with a greater degree and extent of dark/pale contrast than that seen in the other sspp.

The southern African sspp., namely Ourebia ourebi ourebi and Ourebia ourebi rutila, have three features that tend to make the figure somewhat conspicuous.

These are as follows:

The hindquarters show dark/pale contrast, between extensively white buttocks and a black tail. The only other ruminant as small-bodied (14 kg) as O. ourebi, that possesses similar contrast, is the smallest form of gazelle, Gazella saudiya (recently extinct, https://en.wikipedia.org/wiki/Saudi_gazelle).
The ventral white transgresses countershading, by extending far/high enough, on chest, flanks, and buttocks, to catch the light (https://www.inaturalist.org/observations/98375681). This is analogous to the mountain reedbuck (Redunca fulvorufula fulvorufula, see https://www.inaturalist.org/posts/53474-a-comparison-of-adaptive-colouration-between-lookalikes-grey-rhebok-and-mountain-reedbuck#).
The posterior surface of the forelegs, and the anterior surface of the hindlegs, are noticeably whitish.

The differences between the southern African sspp. of O. ourebi and all other sspp. are such that the former can usually be recognised, at a glance, in photos.

The diagnostic features are:

the fluffy appearance of the white fur that crisply borders the fawn ground-colour on chest, flanks, and buttocks, and
the obvious punctuation by the small but consistently dark tail.

The difference is illustrated by the following photo-pair:

Another view:

SOUTHERN first photo in https://www.forestrysouthafrica.co.za/wp-content/uploads/2016/06/Oribi-Case-Study-PRINT-VERSION.pdf, vs
NORTHERN https://www.inaturalist.org/observations/38204111.

In posteriolateral view, the comparison is:

The darkness of the tail shows a clear geographical trend, within O. ourebi, as follows:

In the southernmost ssp., namely ourebi (which extends as far south as the Eastern Cape of South Africa), the tail is consistently black, in all individuals (https://www.inaturalist.org/observations/22457387).
In the northernmost ssp., namely montana/gallarum (which extends as far north as Eritrea), the tail is never black in any individual, and is usually medium in tone, being hardly darker than the fawn ground-colour of the rump (https://www.inaturalist.org/observations/297421).
In the westernmost ssp., namely quadriscopa (which extends as far west as Senegal), the tail seems consistently dark, albeit not black (https://www.inaturalist.org/observations/8490541 and https://www.inaturalist.org/observations/67005602) - but lacks contrast, because the buttocks are not strikingly white (https://www.inaturalist.org/observations/21492170).

Another easily overlooked difference is that the pelage on the underside of the tail is