Adaptive colouration in the puku (Kobus vardoni), an anomalously plain-coloured grazer, part 1

INTRODUCTION

The puku (Kobus vardoni) is one of the many gregarious, grazing ruminants of the world.

However, it is remarkably - perhaps uniquely - plain in its colouration (https://www.inaturalist.org/observations/4901764 and https://www.barclaystenner.com/news/2015/3/27/news-2019-a-leopard-hunting-in-the-kalahari).

This plainness is anomalous, because most of the hundreds of species/subspecies of gregarious ruminants have conspicuous colouration, as follows:

various taxa are conspicuously dark (e.g. Connochaetes spp., Syncerus caffer, Bison bison, many spp. of Cervidae in winter pelage);
several taxa are conspicuously pale overall (e.g. Oryx leucoryx, Nanger dama, Addax nasomaculatus in summer pelage);
many taxa have bold dark/pale patterns - with remarkably diverse configurations - on the rump/buttocks/haunches;
several have bold dark/pale patterns on the face/forequarters (e.g. Damaliscus pygargus, Hippotragus equinus);
a few have conspicuously pale feet (e.g. Giraffa camelopardalis); and
a few advertise caudal erection by means of black (e.g. Gazella subgutturosa) or white (e.g. Rangifer tarandus) pelage on the tail.

The puku is gregarious (https://www.inaturalist.org/observations/192705838 and https://www.inaturalist.org/observations/186871917 and https://www.inaturalist.org/observations/186521396 and https://www.inaturalist.org/observations/182460850 and https://www.inaturalist.org/observations/151233299 and https://www.inaturalist.org/observations/35174040 and https://www.inaturalist.org/observations/9476170).

Furthermore, it resembles 'plains game' in that infants tend to hide in the open, rather than in dense vegetation (https://www.inaturalist.org/observations/19100546 and https://www.gettyimages.co.uk/detail/photo/baby-puku-royalty-free-image/498500801?phrase=puku+kobus+vardonii&adppopup=true and https://www.gettyimages.co.uk/detail/photo/mom-and-baby-puku-royalty-free-image/560145671?phrase=puku+kobus+vardonii&adppopup=true and https://upload.wikimedia.org/wikipedia/commons/e/e9/Puku_female%2C_South_Luangwa.jpg).

However, the colouration of the puku is as plain as that of reedbucks (Redunca arundinum and Redunca redunca, https://www.inaturalist.org/observations?place_id=any&subview=map&taxon_id=42303&view=species). The latter - although also grazers - tend to hide in long grass.

(The following shows how similar juvenile males of the puku can be to reedbucks: https://www.alamy.com/male-puku-kobus-vardonii-beside-a-watercourse-in-south-luangwa-national-park-in-zambia-southern-africa-image597926477.html?imageid=FA280C3B-AA27-4B79-A738-F151C0B479A7&p=11309&pn=1&searchId=356726421c3ae41a10ca229beb33e10d&searchtype=0.)

In reedbucks, concealment is facilitated by

relatively small body size and short horns,
'freezing', crouching, and head-lowering in alarm,
nocturnal activity, and
minimal gregariousness.

Given their ecological nature, it makes sense that reedbucks epitomise the plainest form of cryptic colouration (https://en.wikipedia.org/wiki/Crypsis).

By contrast, the puku poses a puzzle: it is a relatively large-bodied, diurnally active, gregarious ruminant of open vegetation, yet retains plain, ostensibly cryptic colouration.

AIMS

The aim of this Post is to scrutinise in detail the various features of colouration of the puku, in search of clues to

biological relationships (whether homologous or analogous), and
adaptative value (whether residual/incipient or actualised).

RESULTS

I have found various subtle patterns in the pelage of the puku.

These are significant, because they are

in one case, viz. on the posterior surfaces of the ear pinnae, bold enough to facilitate social communication in the puku, or, in other cases, either
faint (=incipient/residual) patterns.

In the latter case, the patterns are either

homologous, i.e. traces of patterns better-developed in other reduncins (https://en.wikipedia.org/wiki/Reduncinae), or
analogous with patterns seen in other clades of ruminants, i.e. subtle cases of evolutionary convergence.

CONSPICUOUS PATTERNS

There is only one conspicuous pattern of colouration in the puku.

Posterior auricular flag

In the puku, the posterior surfaces of the ear pinnae tend to show dark/pale contrast. This is noticeable at some distance, depending on illumination (please bear in mind activation by movement).

close-up:

https://www.shutterstock.com/image-photo/puku-deer-africa-126857135

https://www.shutterstock.com/image-photo/pair-brown-lechwe-antelope-eating-lush-444226501

https://www.inaturalist.org/observations/15905462

(video) https://www.shutterstock.com/video/clip-12992003-puku-sits-on-ground-looks-around-starts

https://www.inaturalist.org/observations/183128180

https://www.inaturalist.org/observations/194037557

https://www.alamy.com/stock-photo-puku-kobus-vardonii-young-rams-chobe-national-park-botswana-125324736.html?imageid=ED843A3C-F7CA-4D3C-BBC6-A294C7E843BD&p=361664&pn=2&searchId=cd244ebf5432c4191236edc6287a8da0&searchtype=0

at distances up to 10 meters:

https://www.inaturalist.org/observations/91942253

https://www.inaturalist.org/observations/8373864

https://www.alamy.com/adult-female-puku-kobus-vardonii-in-south-luangwa-national-park-zambia-image366951605.html?imageid=BFE88D8B-B516-4E5D-BA85-FFC0F47B58DE&p=690600&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.inaturalist.org/observations/183467571

https://www.inaturalist.org/observations/117597482

https://www.inaturalist.org/observations/95744641

https://www.alamy.com/kobus-vardonii-puku-south-luangwa-nationalpark-zambia-image61620422.html?imageid=715775BD-CFC3-460E-AB3D-227777E19F59&p=154309&pn=1&searchId=acc709c179443e5d1df94979b0f1c3a2&searchtype=0

https://www.alamy.com/pukus-kobus-vardonii-in-kafue-national-park-zambia-pukus-kafue-national-park-zambia-image554645609.html?imageid=E9C61A28-AA2B-4268-BCE3-A4BB7C773497&p=2184918&pn=2&searchId=cd244ebf5432c4191236edc6287a8da0&searchtype=0

at distance:

https://www.inaturalist.org/observations/186871896

https://www.inaturalist.org/observations/66963436

https://www.inaturalist.org/observations/65640274

https://www.inaturalist.org/observations/19860792

https://www.inaturalist.org/observations/14508690

https://www.alamy.com/puku-north-luangwa-national-park-zambia-image9033427.html?imageid=10B9D1F3-6053-4070-A778-41E88CBEEA44&p=18535&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.inaturalist.org/observations/194443156

https://www.gettyimages.co.uk/detail/photo/glimpse-of-paradise-royalty-free-image/1124676543?phrase=puku+kobus+vardonii&adppopup=true

The pale effect on the back-of-ear

The relatively conspicuous pattern on the back-of-ear is particularly noteworthy in view of the lack of an anterior auricular flag in the puku, as follows.

In several members of the same genus as the puku, the pelage on the anterior surfaces of the ear pinnae is white with black accentuation. This makes the ears conspicuous enough to constitute an anterior auricular flag (https://www.gettyimages.com.au/detail/photo/waterbuck-royalty-free-image/1320026796?phrase=african+impala&adppopup=true and https://www.alamy.com/waterbuck-face-closeup-image332752171.html and https://www.gettyimages.co.uk/detail/photo/close-up-of-the-head-of-a-male-waterbuck-royalty-free-image/1975503406?phrase=waterbuck+male&adppopup=true and https://www.alamy.com/waterbuck-ugandan-kobus-defassa-queen-elizabeth-national-park-uganda-east-africa-image211288540.html?imageid=A807CDC3-FA5F-449C-A396-CB9605239E42&p=39496&pn=1&searchId=9f12497c29def42bf65a512eafff9f8a&searchtype=0).

By contrast, what is noteworthy about the puku is that its front-of-ear is pigmented enough to dull its appearance:

https://www.alamy.com/puku-moorantilope-image333998332.html?imageid=E1053F55-4D4D-4BD0-8AB5-28C431A29488&p=1151839&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.inaturalist.org/observations/1186419

https://www.inaturalist.org/observations/192639553

https://www.inaturalist.org/observations/185294972

https://www.inaturalist.org/observations/155452720

https://www.inaturalist.org/observations/122317157

https://www.alamy.com/puku-kobus-vardonii-chobe-national-park-botsuana-image360761693.html?imageid=E4C8868D-C329-44A6-83FA-66038A3C7635&p=369970&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.shutterstock.com/image-photo/solitary-male-puku-antelope-kobus-vardonii-1085192051

https://www.shutterstock.com/image-photo/portrait-puku-kobus-vardoni-botswana-8702971

This pigmentation on the front-of-ear detracts from conspicuousness in the same direction - albeit not to the same degree - as in the lion (https://fineartamerica.com/featured/a-lioness-portrait-christopher-miles-carter.html).

INCONSPICUOUS PATTERNS

There are various other patterns in the colouration of the puku. However, all are too faint to qualify as bleezes, flags, or semets.

Dark/pale differentiation between rump and haunch

In the puku, the rump is somewhat darker than the haunches, with a fairly abrupt boundary.

This pattern is

homologous with that in the lechwe (Kobus leche, https://www.inaturalist.org/journal/milewski/90974-lechwe#), in which it is far more conspicuous, and
analogous with that in e.g. hartebeests (Alcelaphini: Alcelaphus, particularly Alcelaphus lelwel).

However, the overall effect is that the colouration of the hindquarters (including the tail) is inconspicuous in the puku.

https://www.inaturalist.org/observations/186614277

second photo in https://www.inaturalist.org/observations/183562322

https://www.inaturalist.org/observations/169920283

https://www.inaturalist.org/observations/152659359

https://www.inaturalist.org/observations/101342161

https://www.inaturalist.org/observations/37101247

https://www.alamy.com/puku-kobus-vardonii-in-south-luangwa-national-park-zambia-puku-south-luangwa-national-park-zambia-image554645894.html?imageid=5947E7F8-BF9A-45FE-9C28-F283212ED2BF&p=2184918&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.alamy.com/female-puku-kobus-vardonii-standing-in-grassland-in-south-luangwa-national-park-in-zambia-southern-africa-image597927112.html?imageid=B1D5916E-9A78-4B99-9E54-D54026E89FF7&p=11309&pn=1&searchId=660be775941111ad3ff09a1a1eb9c3a4&searchtype=0

https://www.shutterstock.com/image-photo/wild-puku-antelope-african-savannah-427182217

https://www.shutterstock.com/image-photo/puku-photographed-bush-zambia-23460037

https://www.alamy.com/kob-hind-and-fawn-disturbed-at-a-salt-lick-mole-national-park-northern-image1833508.html?imageid=5BE18701-13D7-491E-9BCB-4940D6D1E1B3&p=54834&pn=7&searchId=b27cc7ee52bb614a82ca2293933ebfc9&searchtype=0