Intriguing parallels between gelada and spotted hyena, including 'sexual mimicry'

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There are some strange parallels between the spotted hyena (Crocuta crocuta, https://www.inaturalist.org/taxa/41886-Crocuta-crocuta) and the gelada (Theropithecus gelada, https://www.inaturalist.org/taxa/43530-Theropithecus-gelada).
 
The gelada shows oestrus, as do other baboons. However, this is not by means of perineal/vulval/buttock displays, but instead by means of an unique display on the chest of females.

This is odd. However, it makes sense, because the gelada is such a specialised grazer. It grazes in a sitting and shuffling position (https://www.inaturalist.org/observations/93080317 and https://www.alamy.com/gelada-gelada-baboons-theropithecus-gelada-geladas-in-semien-mountains-ethiopia-simien-mountains-national-park-image255379044.html?imageid=E4CA439C-8E1D-4D90-ADE7-6A9365A61FF4&p=853427&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0).

Thus, the posterior is hidden most of the time.

In females of the gelada, the chest resembles the posterior/genital display of other baboons. The following show how fluid-filled the chest of the female becomes in oestrus: http://cdn.c.photoshelter.com/img-get/I0000WFL6ZtWHzZw/s/600/600/3052719.jpg and http://mammiferesafricains.org/wp-content/uploads/2014/02/Gelada25.jpg and https://drscdn.500px.org/photo/6726246/m%3D2048/bd32c4f58de06bcd4ff04cae9d7900dc and https://www.alamy.com/stock-photo-gelada-baboons-theropithecus-gelada-34568792.html?imageid=14BDE9A5-BABD-468C-88E3-72872AE2DF8A&p=31437&pn=2&searchId=43b4fd56c18e613f5a6c934ff23fa90c&searchtype=0.

This is the equivalent of the extreme swelling and colouration of the posterior in other baboons (https://onlinelibrary.wiley.com/doi/10.1002/ajp.22154). (In the gelada the hue of females' chests changes with age rather than with the oestrus cycle.)

So far, we have something remarkable, but not particularly puzzling. It is only about as odd, in its own way, as the complex anal glands and anal pouch of the spotted hyena. Both are morphological specialisations, in keeping with ecological specialisations.
 
What seems more anomalous in the gelada is as follows.

Mature males, although possessing clearly masculine feature, seem to mimic the sexual display of females.

Males, like females, have an hourglass-shaped bare patch on the chest, with a conspicuous pinkish hue (https://www.gettyimages.in/detail/video/red-skin-patch-display-on-chest-of-male-gelada-stock-video-footage/1B05613_0050 and https://www.alamy.com/stock-photo-gelada-baboons-theropithecus-gelada-mating-in-simien-mountains-national-49972611.html?imageid=7F7B4936-26ED-4FCB-9CD1-E2C1B43A82EB&p=164920&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/geladas-in-ethiopian-higlands-image342182110.html?imageid=2B6EC72D-42AC-4B5F-9AB3-EE82432820DC&p=1245774&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/gelada-theropithecus-gelada-captive-image370935491.html?imageid=97AF3E0F-D629-4316-8383-F816D6D7EA4E&p=377338&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/male-gelada-theropithecus-gelada-monkey-in-semien-mountains-ethiopia-image231468539.html?imageid=1BF8A4CB-1ABC-4448-B250-9DB953B5E983&p=181514&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/stock-photo-gelada-baboon-theropithecus-gelada-male-animal-animals-baboon-baboons-20626358.html?imageid=B0B5E654-B0CA-450F-AA97-A03AE0CB6727&p=32975&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0).

In males of the gelada, the arrangement of pelage and skin-creases gives this display a genital gestalt, somewhat vulva- or buttock-like. The chest display of mature males has no masculine overtones in common with any other mammal I know of, human chest hair notwithstanding.

In the spotted hyena, the sexes have similar body size and shape, with females somewhat more massive than males. This contrasts with the gelada, in which males are by far the larger-bodied sex. Mature males are about 18.5 kg, compared with 11 kg for adult females (https://www.alamy.com/stock-photo-geladas-theropithecus-gelada-pair-standing-on-rock-captive-switzerland-72476141.html?imageid=22171D4E-4CEB-49E2-AA88-52E2BA9174E2&p=94339&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/stock-photo-three-geladas-theropithecus-gelada-18357887.html?imageid=88301E82-A2A4-44A1-9FCD-2E0D0FC8ACA9&p=65924&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.mindenpictures.com/stock-photo-gelada-baboon-theropithecus-gelada-female-and-male-simien-mountains-naturephotography-image00554829.html).

The following again shows the sexual dimorphism, as well as the similarities and differences in the chest display http://2.bp.blogspot.com/-FKroMTJ5otI/T7NdWYP1VkI/AAAAAAAAA54/nv7uQByDPXw/s1600/Gelada7.jpg. The female here is at a stage of the oestrus cycle when fluid-vesicles appear temporarily on the chest.

Thus, males seem, in a way, to be showing sexual mimicry.

In the spotted hyena, females seem to mimic males; in the gelada it is males that seem to mimic females.
 
There is also a parallel in the bringing of the teats into the genital display.

I have mentioned in other Posts that the teats of the spotted hyena are located in the groin. This means close to the clitoris, in this species with its odd genitalia.

In the case of the gelada, the oestrus display involves the teats, because both are located on the chest. (Note that, as in other cercopithecids, the teats are extremely close together, enabling the infant to suckle from both at once, https://www.alamy.com/stock-photo-a-young-gelada-sits-next-to-its-mother-in-the-simien-mountains-ethiopia-110606213.html?imageid=FC60FF7A-3A61-4252-8C28-FC7E571EA5B4&p=29755&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0.)

So, it seems that, in both primate and carnivore, there is not only some sort of ‘sexual mimicry’ but also a level of ‘co-location’ of the genital organs and suckling organs. In other baboons, after all, the teats are on the chest, far from the genital display on the posterior.
 
What may be relevant here is that the gelada seems to differ from other baboons in courtship. The gelada does not seem polygamous in the same sense as other baboons are.

In other baboons, males tend to be sexually coercive. In the gelada, females take the main role in choosing males, and soliciting their attentions. Females seem to be in social control in the gelada, despite being far smaller, weaker, and less armed than males are. The society is largely controlled by females, with a female hierarchy that seems independent of males. It is females that show most of the aggression among ‘breeding units’.

Furthermore, infanticide by males is rarer than in other baboons, because pregnant females can spontaneously abort instead (https://en.wikipedia.org/wiki/Bruce_effect).
 
A second surprising parallel between primate and carnivore is in vocal complexity, i.e. language.

The vocalisations of the gelada are so complex that they seem to qualify as language (https://en.wikipedia.org/wiki/Gelada). This reminds me of the spotted hyena, which is by far the most vocal and linguistically versatile of Carnivora.

I have yet to understand why language is so much better-developed in the gelada than in other baboons. However, I suspect that in both gelada and spotted hyena there are, to some degree, separate ‘dialects’ for males and females.
 
This leads me to make a new connection: that in courtship the gelada uses ‘visual persuasion instead of rape’, as it were. And that, in its own way, the chest display of males is some sort of ‘feminist signalling’.

In the spotted hyena, females have ‘stolen’ the identity of the phallus to the degree that its ‘perversion’ has spread even to the penis. Males of the spotted hyena do not erect the penis as a sign of assertion/confidence.

Similarly: in the gelada, males have appropriated the appearance of the feminine posterior (wearing it as a T-shirt, as it were). Males seem permanently to wear insignia of solidarity with females, despite their greater brawn and incomparably more dangerous canines. This differs from other baboons.
 
Do readers see the emerging analogy?

In the spotted hyena, the society combines sexism with a remarkable bending of genders. Even the vocalisations seem sexist, in the sense that females usually ignore the whooping call if it is made by males. This implies that even conversations in the spotted hyena are split into those among females, and those among males, despite the ostensible 'masculinisation' of females.

In the gelada, the society is also surprisingly ‘feminist’, despite superficial appearances to the contrary.

I suspect that the body size, cape/mane, and canines of males may be more for protection of the group against predators such as the leopard (Panthera pardus), and less about sexual dimorphism for courtship and polygamy.

Although mature males of the gelada may be anti-predatory warriors, their masculinity may possibly be analogous with that of the spotted hyena in submitting to sexual control by females.

A third parallel can be found in facial expressions.

Both the gelada and the spotted hyena expose the teeth and gums more than other baboons and other Carnivora, respectively. In the gelada this exposure is owing to a remarkable morphological specialisation.

Both sexes can flip the upper lip upside-down/inside-out, exposing a conspicuous pinkish area of the gums, as well as the incisors and canines (https://www.alamy.com/gelada-baboon-theropithecus-gelada-with-its-mouth-wide-open-stuttgart-image62156981.html?imageid=6E419A8B-F48D-4146-8F17-E0AC5C808AB1&p=165061&pn=2&searchId=43b4fd56c18e613f5a6c934ff23fa90c&searchtype=0 and https://www.alamy.com/the-geladas-have-four-inch-long-incisors-as-herbivores-these-are-primarily-for-fighting-simien-mountains-national-park-ethiopia-meet-the-adultero-image426583285.html?imageid=4F83387B-9727-4746-908A-0BCF6AF7A74B&p=403504&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0 and https://www.alamy.com/stock-photo-gelada-baboon-theropithecus-gelada-adult-male-close-up-head-folding-47752681.html?imageid=35BAFA03-C064-482F-A8E4-0DD8B5FA03B4&p=11592&pn=2&searchId=43b4fd56c18e613f5a6c934ff23fa90c&searchtype=0 and https://www.alamy.com/gelada-baboons-baring-teeth-in-the-simien-semien-mountains-national-park-ethiopia-africa-image216176155.html?imageid=A7836037-B652-4A73-B3AD-ADA3E903DECC&p=230145&pn=1&searchId=480dd3191edee4e232cf1a69495fef1a&searchtype=0). This is not necessarily fang-baring of the threatening/defensive kind.

The spotted hyena exposes its gums most completely in fear or humour rather than in anger, by drawing the gape far back (https://www.youtube.com/watch?v=4gKUSvmxRs4 and scroll in https://www.sabisabi.com/blog/7936/wild-dog-vs-hyena/). It does not seem to expose the canines or the cone-shaped, bone-cracking premolars to signify threat.

The gelada exposes its gums most completely in fear or humour, by flipping the upper lip. Females expose the canines, despite these being so small that the expression actually exposes vulnerability. The following shows the fear-grimace (or possibly happy-grin) of adult females: https://stock.adobe.com/images/big-mouth-of-a-endemic-female-gelada-baboon-to-a-male-in-the-simien-mountains-national-park-in-ethiopia/198393861 and https://c1.staticflickr.com/9/8169/7992284573_abeee57402_h.jpg and https://www.naturepl.com/stock-photo-gelada-baboon-theropithecus-gelada-female-lip-flipping-as-a-sign-of-image01247223.html.

The spotted hyena has shifted its sexual opening far forward, converted the clitoris to a phallus, and created a pseudo-scrotum. For its part, the gelada has shifted its perineal/vulval/buttock display to the front, and placed feminist insignia on males' chests. Both expose their gums/teeth in odd ways, poorly-described as 'fang-baring'.
 
The conversion of the chest to a sexual display is not unique to the gelada among primates. A more familiar case is female breasts in Homo sapiens.

In both cases, one of the reasons seems to be the adoption of an upright posture. In the case of the gelada, this is a sitting posture, but an upright one nonetheless. Where humans differ from the gelada is that men have no sexual mimicry of women.

FOOTNOTE on fang-baring, grinning, smiling, grimacing in the gelada and other baboons:
  
My reference is Estes (1991) on the topic of facial expressions in baboons and Old World monkeys.

Cercopithecoid monkeys and anthropoid apes do smile in a sense, implying that it is not after all uniquely human to smile. The expression is called not a smile but a ‘play face’.

The configuration of the mouth is similar to that of the aggressive fang-baring expression, but the eyes look different. “The teeth are bared as in bared-teeth threat but there is an obvious difference in the eyes, which are often slitted or partially closed, never staring”.
 
Apart from the opening of the jaws, why could this not be called a ‘happy-grin’? I do not see the openness of the mouth as a disqualifying factor, because baboons also perform the fear-grimace, at least part of the time, with an open mouth.
 
Could it be that many of our relatives smile in a way that is both homologous and analogous to our human smile? I suspect that, if anyone has discussed this informatively, it will be Desmond Morris.
 
Baboons have both visual and audial displays of their dangerous canines. They ‘fang-bare’ conspicuously by both yawning and the ‘canine threat display’. However, they also use what Estes describes as ‘tooth-grinding’. I suspect that it is not the molars that are being grinded here, but the upper canines against the lower premolars. The latter act as ‘whetting stones’. I.e. when a male baboon grinds its teeth it is actually sharpening the canine, and the sound warns the other, by implying the sharpness of the canines.
 
Is there any Carnivora that has an audial display of the canines? I suspect not. In this sense, primates outdo carnivores: their canines are in some species proportionately larger than those of carnivores; the canines remain sharp because they are whetted against a special lower premolar; and there is an audial as well as visual display of the canines. Balancing this, though, is the fact that, in most primates, females have far smaller canines than males (I seem to recall this is not true for gibbons and I need to check which other species of monkeys and apes have impressive canines in females).
 
Estes (1991) does not feature the gelada. However, photos on the web show that females of the gelada often uses an expression that is either an assertive fang-baring or a fear-grimace. I suspect that it is mainly a fear-grimace, although not usually described as such. One of my reasons is that the canines, although discernible, are not big enough to be dangerous-looking in females of the gelada. If I am right, the main difference between the gelada and other cercopithecids is the lip-flip performed in the nominally fang-baring expressions (yawning, fear-grimace, canine threat in males, etc.).
 
Estes (1991) indicates that, in not only baboons but Old World monkeys in general, the penis is used to display confidence, self-assertion, and status, way beyond any purely sexual communication. For example, not only baboons but most cercopithecid monkeys have a display in which a mature male takes a sentinel role, guarding over the group, with his legs slightly spread, and his penis partly erected, the conspicuousness of the penis accentuated in some species by bright hues. The non-sexual display of the penis is different in Old World monkeys and baboons on the one hand, and the spotted hyena on the other. In the former, the display of the penis is assertive, whereas in the latter the display of the penis is submissive/self-effacing. I have not found anything in the literature that actually states this basic difference. However, it seems obvious when one thinks laterally. This would affect our interpretation of the peniform clitoris of Crocuta.
 
Coming back to the face: one of the main differences between monkeys and the spotted hyena is that in the former the eyebrows and eyelids are used in various facial expressions, in combination with the mouth. The eyes are more expressive in hyenas than in felids, canids, viverrids, etc.. However, the spotted hyena has no eyebrows and no display of the eyelids. The closest thing I have seen to the primate pattern is the complex wrinkling of the skin on the forehead, particularly right between the ears. This gives the spotted hyena a quizzical look, in a subtle way.
 
The gelada and the spotted hyena both show the fear-grimace in extreme ways, by particularly stretched mouths. In the spotted hyena it is mainly the gape that stretches to the maximum in the fear-grimace (https://www.youtube.com/watch?v=4gKUSvmxRs4), while in the gelada it is mainly the upper lip, which actually flips inside-out. It remains to be seen whether the gelada ‘smiles’ (i.e. a happy expression) with the lip-flip, i.e. whether it possesses a positive version of the fear-grimace that also shows the maximum exposure of the upper gums. If so, I doubt whether any primatologist has noticed it, for more or less the same reasons as I have explained elsewhere, w.r.t. the failure to notice the fear-grimace in the human species.
 
It may transpire that both the spotted hyena and the gelada have a ‘happy-grin’.
  
Theropithecus gelada female, probably fear-grimacing:
http://www.shahrogersphotography.com/gallery/Upload/SM08FR-520.jpg

Publicado el julio 17, 2022 04:20 TARDE por milewski