Interspecific variation among baboons in the anatomy of the posterior, including ischial callosities and oestrus swellings
(writing in progress)
Ischial callosities, associated bare skin, and oestrus swellings are characteristic of baboons and other supersocial cercopithecids.
Their anatomical structure, function, and colouration in the various species of baboons are confusing.
Some naturalists think that the various forms of savanna baboons are just subspecies. Hiwever, they differ far to much to be anything less than different species.
This can be seen in the ischial callosities.
These function non-sexually. as pads for sitting, but are surprisingly different among the various species of savanna baboons (Papio).
For example, the chacma baboon (Papio ursinus) has the smallest ischial callosities, illustrated in the following photo in the adult male.
Papio ursinus adult male:
https://s-media-cache-ak0.pinimg.com/736x/22/6d/02/226d02b73e1017f4adfb3feaf3da9b5a.jpg
In the female of the chacma baboon, the ischial callosities are similarly modest, but the adjacent oestrus swellings are complex and dynamic.
In the following photo we see how the pink oedema has spread from the anus-vulva area laterally. I find it remarkable that the oestrus swelling seems to ‘focus’ on the anus as much as the vulva, with the result that the vulval area is inevitably contaminated by faeces and the male must surely be introducing faecal matter inadvertently to the reproductive tract of both himself and his partner when he copulates. I don’t think this has been thought through enough.
Please note that the ischial callosities in the female remain visible as distinct from the oestrus swelling, although they a) go pinkish, and b) tend to be overlapped by the swelling.
Papio ursinus adult female early in oestrus swelling:
http://thumbs.dreamstime.com/z/female-chacma-baboon-sexual-organs-south-africa-23299849.jpg
In the following photo (on right) we see how large the oestrus swelling can be in the chacma baboon. It has spread laterally to the haunches, dorsally to well above the anus, and ventrally from the perineum to the crotch. The ischial callosities, still pinkish in contrast to the dark grey ones of the male (and presumably the non-oestrus female) are still largely visible, so this female can still sit, although sitting is uncomfortable.
As an aside, just look at the head of this female, particularly the illusion of a small cranium owing to the low forehead. Consider that this animal, of body weight about 15 kg, has a brain fivefold larger than that of a large species of wallaby of similar body mass?
(right-hand photo) Papio ursinus adult female with maximum oestrus swelling:
https://www.researchgate.net/profile/Joanna_Setchell/publication/46182259/figure/fig2/AS:267692057821234@1440834168752/Figure-2-Primate-ornaments-that-signal-the-possession-of-specific-MHC-class-II.png
The following photo shows the male and female of the hamadryas baboon together for scale. This female individual is approaching oestrus, as you can see by here pink oedematous swelling which makes sitting uncomfortable for her. But what is remarkable is that in this species, the male MIMICS the female by having large areas of bare skin, associated with the ischial callosities, that are conspicuously pink. The function of these swellings, which are permanent as long as the male is in his prime, is to appease attacking males by means of effeminate presentation of the posterior. Please note the irony: the male of the hamadryas is far more ‘macho’ than that of the chacma in his grey cape, white facial ruff, and even the deep jaw; but on the other hand he has an effeminate posterior.
Papio hamadryas:
https://upload.wikimedia.org/wikipedia/commons/c/cb/Papio_hamadryas_pair.jpg
The following two photos show just how extraordinarly massive the oestrus swellings can become in the hamadryas baboon in captivity. I emphasise that this is NOT pathological, it is ‘normal and healthy’, with the caveat that such extremes are seldom observed in the wild. The effect is particularly startling, considering that in every other way the female of this species is so ordinary as to be nondescript.
The second photo shows how, partly by virtue of complex creasing, the contamination of the vagina by faeces seems almost guaranteed. What on Earth is going on here, in terms of adaptation? Note that the ischial callosity is completely covered by this swelling, which means an extreme that I do not think the chacma baboon reaches.
Papio hamadryas adult female at peak of oestrus swelling:
http://2.bp.blogspot.com/-BObI2vJEHwc/Udg82oqq-AI/AAAAAAAACv8/kWTJuTpjjI4/s1600/baboon-swelling.jpg
Papio hamadryas adult female at peak of oestrus swelling:
http://i.imgur.com/jhW2kKA.jpg
The final photo once again shows the mature male of the hamadryas baboon, emphasising that it is normal for the male to have a pink butt superficially similar to the oestrus swelling of the female. I have yet to get to the bottom of where the ischial callosity begins and ends in this species, but I think this pink swelling is tough and quite comfortable for the male to sit on.
Papio hamadryas adult male in his prime:
http://www.angelfire.com/super2/claire_loves_geordie/images/baboon2.jpg
There are at least five complications to bear in mind when looking at the posteriors of baboons (genus Papio), in addition to gender.
Firstly, the chacma baboon tends to have minimal exposure of a bare dark patch of skin lateral to the ischial callosity. The five other species have this bare patch more prominent than in the chacma.
Secondly, in the hamadryas the male has pinkish, mimicking the female.
Thirdly, the oestrus swellings become larger and more extensive as ovulation is approaches.
Fourthly, the oestrus swellings tend to be larger and more extensive in zoos than in the wild.
Fifthly, the two other genera (Theropithecus and Mandrillus) differ considerably from Papio.
The following shows the yellow baboon, in which there is a clear difference in tone and hue between the ischial callosities (flesh-coloured) and the bare patches lateral to these. I assume that these dark grey bare patches are bare owing to the fur being worn off during sitting. However, these patches (which have thick but not necessarily callous skin) vary considerably in extent and colouration in various species of baboons.
Papio cynocephalus probably subadult male:
http://cache4.asset-cache.net/gc/537007621-yellow-baboon-walking-on-roof-with-broken-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=EjsHGVE%2BEK2PNY6JdwOOA9xzgZo%2B4b%2Bf3YXUWhFXFOc2BvVLxDPItvo1QfwIdomh
In the following photo of the anubis baboon, the tail has been amputated, possibly by a rival male. This nicely reveals the precise location of the anus. As in the yellow baboon above, the ischial callosity is more flesh-coloured than the bare patch lateral to it, but the difference is that in the anubis baboon this bare patch is more clearly defined, as if to suggest some sort of display.
Papio anubis adult male:
http://voices.nationalgeographic.com/files/2014/07/De-Jong-Butynski-Olive-baboon-Meru-1.jpg
In the adult female of the anubis baboon, this lateral bare patch is likewise clearly evident, which is a point of difference from the chacma baboon. If one looks at females of the chacma baboon in e.g. Kruger National Park, one will not see such a clear, bald, shiny, dark grey patch on the buttocks of the anoestrus stage (which occupies about a third of each month).
Papio anubis adult female with no oestrus swelling:
http://cld.persiangig.com/preview/NmQnP8sz4M/olive_baboon_514hornsby.jpg
The following shows how much less noticeable the bare patch is in the anoestrus stage in the chacma baboon. Note that the ischial callosities seem identical in size and colouration between chacma and anubis baboons.
Papio ursinus adult female with no oestrus swelling:
http://travel4wildlife.com/wp-content/uploads/2012/09/baboon.jpg
In the guinea baboon (which is a small species similar in body size to the hamadryas), the bare patch lateral to the ischial callosity is more like the anubis than like the chacma in appearance. However, this species holds its tail differently from the chacma, lacking the characteristic kink of the latter species.
Papio papio adult female, with no oestrus swellings:
http://www.animalphotos.me/mamm2/bab-guin_files/guinea2.jpg
The following shows that the bare patch lateral to the ischial callosity is fairly obvious in the male of the guinea baboon. Note again how different the tail is from the chacma baboon. And of course the face is different as well, because in the guinea baboon the forehead and muzzle are parallel, whereas in the chacma one is at an angle to the other.
Papio papio adult male:
http://www.animalphotos.me/mamm2/bab-guin_files/guinea1.jpg
The following is another view of the prominent bald patch on the posterior of the male (and female) of the anubis baboon. However, note that the tail is more similar to that of the chacma than that of the guinea baboon.
Papio anubis adult male:
https://www.aboutanimals.com/images/olive-baboon-savanna-820x459.jpg?c7dc04
The following shows the female of the chacma baboon with oestrus swelling. Note how the skin around the anus has swollen, as well as the skin from perineum to vulva. The anal opening is the slit just below the base of the tail, with the vulva so close to it that contamination with faeces is inevitable and seems to be part of the adaptive design for some reason. Note that the dull flesh-coloured ischial callosity is still visible although the left and right sides seem to have been forced apart and each is being partly overlapped by the sexual swelling. This individual does have a definite bare patch lateral to the ischial callosity, but this is likely to be subsumed by the pinkish sexual swelling by the time of ovulation.
Papio ursinus adult female with oestrus swelling:
https://cdn.superstock.com/4141/Download/4141-16725.jpg
The chacma baboon has minimal development of the bare patch on the buttocks, but shows instead a pair of pale patches of pelage on the mid-muzzle.
The following specimen of the adult male chacma baboon shows what is about the maximum development, for this species, of the bare patch on the buttocks, which is lateral to the ischial callosity (which is not visible in this view). It’s certainly true that this bare patch is more poorly developed in the chacma baboon that in any of the other four species of baboons, but it is not quite absent.
I am not sure why a pale patch appears on the cheeks in this view. There is no facial ruff in the chacma baboon but it seems that there is a modest ‘sheen’ effect in this area?
Another feature that somewhat surprised me in this specimen is the semi-tassel on the tail.
Also note the paleness of the upper eyelids, which I think is true of all species of baboons although in the hamadryas the pale is more a function of a combination of half-closing the eyes and raising the skin on the ‘eyebrow ridge’ (which of course lacks eyebrows in the sense of pelage).
Photo of chacma baboon showing maximum development of bare patch of skin on buttocks:
Papio ursinus adult male in northeastern Namibia:
http://previews.123rf.com/images/thoron77/thoron771003/thoron77100300014/6552529-Male-baboon-in-Mahango-Game-Reserve-Namibia-Stock-Photo-baboon.jpg
The yellow baboon (Papio cynocephalus) is goegraphically intermediate between chacma and anubis baboons, so we should perhaps expect this species to shown an intermediate pattern. And this more or less turns out to be true, although one’s eye tends to be distracted by the fact that this is the rangiest in build of all the baboons.
In the following series of photos (all of which refer to adult male Papio cynocephalus) I show that the yellow baboon:
a) does possess a clear bare patch on the rump, but this seems paler than in the anubis baboon, perhaps in partial matching with the paleness of the cheeks,
b) does possess pale patches on the mid-muzzle, as well-developed as in the chacma baboon.
So, overall the yellow baboon seems to combine the muzzle-patches of the chacma baboon with something approaching the rump patches of the anubis baboon, but differs from both in that it has conspicuously pale cheeks. These cheeks are not ruffed as in the anubis baboon, but paler than the nondescript cheeks of the chacma baboon.
The yellow baboon is thus harder to interpret than the anubis or chacma baboons, but at least this series of photos documents its pattern to some degree.
http://3.bp.blogspot.com/-NRzkkE0FGbc/TjI1_w5U4HI/AAAAAAAADHI/LncBCCSTefs/s400/yellowBaboon1_920.jpg
http://l7.alamy.com/zooms/4e25d25b87a743fda2266eaebb80c6f0/yellow-baboon-savannah-baboon-anubius-baboon-olive-baboon-papio-anubis-ebnk67.jpg
http://thumbs.dreamstime.com/z/yellow-baboon-3103920.jpg
http://pin.primate.wisc.edu/fs/sheets/images/278med.jpg
http://cache4.asset-cache.net/gc/128111537-rear-view-of-yellow-baboon-papio-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=feJtx6rXFRNqHW1SdJqosoh0A6e5HeurBGAdC83VOWLVxS%2BuAAwBfXN4dsL%2B8gsN
http://www.lolldaiga.com/wp-content/uploads/De-Jong-Butynski-P.-cynocephalus-Kitobi.jpg
(writing in progress)
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