Preliminary attempt to list the exceptional/unique features of the spotted hyena
(writing in progress)
Just what are the exceptional or unique attributes of the spotted hyena?
Only once these features have been established can we really begin to interpret the life history strategy and ecology of the species meaningfully, something which will presumably allow us to explain, in a deep and insightful as opposed to shallow and mechanistic way, the unique genitalia of the female spotted hyena.
Exceptional dentition because the spotted hyena combines well-developed canines and carnassials with unique bone-crushing premolars. No other Carnivora but hyenas have similar dentition, but we still need to establish clearly just how the spotted hyena differs from other hyenas in its dentition.
Exceptional sexual monomorphism until puberty (after which this tends to break down because of the conspicuousness of udder and nipples).
Exceptional emphasis/reliance on lactation. We should find out if any other Carnivora show parallels in this.
Exceptional incongruity between overall colouration (disruptively spotted) and behaviour (not remaining stationary in a way that would allow camouflage to work). The spotting of the spotted hyena has never been functionally explained, i.e. its adaptive value remains unknown.
Exceptional bottleneck in birth canal. I know of no mammal comparable to the spotted hyena in this feature.
Exceptional bias towards females and against males in overall social status, i.e. exceptional superiority of females over males in the hierarchy of power within the species. This is only partly described by the word ‘matriarchal’, but we should review which other Carnivora are considered matriarchal, something that will require careful definition of the word ‘matriarchal.’
Exceptionally penis-like clitoris. I don’t think there’s any animal on Earth that matches the spotted hyena in this way.
Exceptionally selfish sociality (as opposed to altruistic).
Another way of rationalising our new explanation of bottleneck in birth canal of spotted hyena:
What is to be explained?
The fact that the spotted hyena has evolved a bottleneck in its birth canal, so tight that it poses lethal risk – certainly to the first neonate but even to some extent to the mother. Labour can be so hard (constraints on the stretching of the urinogenital passage within the fully flaccid and partly retracted peniform clitoris) that there can be such delays and such physiological distress that the neonate dies during parturition.
My new explanation:
This is a self-imposed handicap but the payoff is in social status and the improved access to food in intraspecific competition. Perhaps about half of all female individuals fail to produce a living neonate in the first birth of their lives, but the ca 50% that do succeed may enjoy a sudden hike in their social status, which allows them to dominate certain other individuals at kills. These young female individuals will of course probably not be superior to many of the female individuals in the clan, but the point is that any hike in status is better than hierarchical stasis or loss of rank.
The mechanism: after a young female individual gives successful birth on her first-ever attempt, and she begins suckling her infant, she has a way of communicating this genuine success on her next greeting of hierarchically similar ‘peers’ in the clan.
I suspect that the way she goes about this is to ignore ‘peers’ with whom she previously demoted herself, which implies new superiority. This would provoke an initiation of greeting by the ‘demoted’ individual, which would – I suspect – be the one to erect her peniform clitoris (whether intact or freshly torn from unsuccessful first birth) for olfactory inspection. The result of this greeting would be that the successful female individual would walk away as a recognised superior to the other individual concerned despite having been an inferior previously.
Even is this reshuffling applies to only a few individuals (all of them female of course) in the whole clan, it is probably worth it in terms of foraging success. This is because in the social system of the spotted hyena there are few opportunities for advancement; the hierarchy tends to be set by inheritance and one of the few ways to promote oneself is to pass the self-imposed test of first birth.
In this explanation, the peniform clitoris emerges as the instrument, as it were, of both demotion and promotion. It is an instrument of demotion because its erection signifies acknowledgement that the social status has remained inferior or is newly inferior.
I am referring here to the greeting ceremony. It is an instrument of promotion because its injury during birth, combined with the olfactory proof of suckling, signifies a kind of kudos that excuses that particular individual from demoting herself on her next encounter with a ‘rival’ individual of comparable rank.
Among Carnivora, and mammals (and other animals) in general, there is a certain trade-off between QUANTITY and QUALITY of reproduction.
Essentially, animals can either pump out lots of infants which tend to die like flies, ore they can concentrate their investment into a few individual offspring which are carefully nurtured. We see this principle even within e.g. Felidae: for example the cheetah has a larger litter than the coexisting leopard, i.e. the cheetah goes more for quantity than the leopard which goes more for quality.
Of course, many variables contribute to the quality/quantity distinction, of which litter size is only one. And all species of Carnivora do have a quantity aspect as well as a quality aspect to their reproductive strategy. But the point is that the spotted hyena, perhaps more than any comparable carnivore, tends to go for quality at the expense of quantity, in keeping with its relatively long life, relatively great intelligence and capacity for lifelong learning, and relatively complex society.
So, the spotted hyena is an unusual carnivore in that it combines a quality-based reproductive strategy and an extremely complex society (something which I think tends to go with quality-emphasising reproduction throughout the animal world) with EXTREME SELFISHNESS and a strategy in which there is MINIMAL altruism (of the sort seen in e.g. the African hunting dog Lycaon pictus).
Clearly, the spotted hyena is extreme in that it attempts quality-based reproduction despite being about the most SELFISH of social carnivores on Earth. Were it solitary in its social system, this might not be a surprise.
But it is extremely social, with clans of up to about 100 individuals and ‘cooperative’ (actually just collective/gregarious in most instances, because the basis of getting together is competitive rather than collaborative) foraging (mainly in defence against other Carnivora) and denning. I could perhaps put it this way: the spotted hyena manages to reproduce in a quality-emphasising way despite receiving no intraspecific assistance.
The mother in the spotted hyena gets no help from anyone despite living in a complex society. She gives birth alone in a hole or thicket, even though the offspring will usually den a few weeks later as part of a collective (the clan usually has one denning site that is being used at any one time). Her most difficult of parturitions is endured alone in the world, with no sisterly help or comfort.
When she reproduces again later in life, her surviving daughter gives her no help, in contrast to e.g. canids in which such help is routinely offered. The father provides no paternal care whatsoever. Even her sisters will probably not bother to suckle her offspring in emergency when the mother’s return from foraging safari is delayed.
The ‘cooperation’ at the clan’s denning site is nothing more than passive protection by any adult individual who happens at the time to be attending her own offspring; i.e. no adult actively defends anyone else’s offspring and the den works purely gregariously as opposed to collaboratively.
There may be ‘strength in numbers’ but in the spotted hyena it cuts both ways. This is because the more competitors the more hectic the competition. So the mere facts of gregariousness and social complexity in no way imply, per se, that any individual spotted hyena is ever deliberately assisted – in anything it ever attempts – by any other individual. If it is a case of strength in numbers, it’s almost as if this is by default, the side-effect of collective competition.
What the literature does not emphasise enough, I feel, is how surprising it is that the spotted hyena specialises on quality-based reproduction despite its lack of altruism.
What is unique/extreme is its combination of three things: extreme selfishness, extreme social complexity (I choose this rather than extreme gregariousness because much of the social complexity is enacted virtually via olfaction, rather in real time via vision), and extreme parental investment (few litters, small litters, slow growth, rich milk produced during prolonged lactation, plus inheritance of rank from mother).
Perhaps that’s worth repeating: the key to understanding the bottleneck in the birth canal of the spotted hyena is the species’ unique combination of extreme selfishness (= lack of altruism) with extreme social complexity with extreme parental investment.
If the spotted hyena manages to make extreme parental investment in a few offspring despite its lack of altruism, perhaps the peniform clitoris is the organ in which this unusual approach is most embodied?
Confirmation that first birth is dangerous in spotted hyena, plus details of sexual differences in peniform organ:
The following paper confirms that, based on the captive colony at Berkeley, about 60% of first births produce a stillborn neonate.
This paper also describes in detail the differences between the penis and the peniform clitoris. They are similar for sure, but not identical by any means. The differences are gross enough that they should be readily visible intraspecifically. The flexibility of the penis exceeds that of the peniform clitoris, the opening at the end is dorsal in male and ventral in female, and the glans is angular in male and round in female, etc.
It strikes me for the first time that there may be some analogy between self-imposed stillbirth in the spotted hyena and infanticide in e.g. the lion.
In the lion, the basic puzzle is why the male kills juveniles of his own species. There is a payoff which arguably leaves the species as a whole better-off, but nonetheless it is counterintuitive that the lion should itself be responsible for killing conspecific infants, given all the other species of carnivores out there that would love nothing better than to commit this infanticide = murder.
Given the hatred among lion, hyenas, leopard, canids, etc., you’d think that the last thing that would evolve within the lion species would be infanticide, and the last reaction to this murder that would evolve in the mothers is to turn willingly to the murderers for the next copulation, in short order. Yet this is what actually happens: a measure of suicide at the species-level.
At it seems adaptive in a roundabout way. The obvious benefit is that the juvenile-killing male individuals provide excellent protection to their own cohort of offspring and that this results overall in improved reproductive success, a case of ‘being cruel to be kind’ in an intraspecific sense.
Could it be that in the spotted hyena there is something similar going on: that it is somehow a case of cruelty-to-be-kind when the first offspring of a given individual female dies in parturition? If so, what could the indirect payoff be?
One possibility would be that the female individual gets an instant kick up the hierarchical ladder if she gives birth successfully to her first litter (which usually consists of one). This would be easy, of course, for other female individuals to detect in the greeting ceremony, based on hormones and the obvious damage to the clitoris.
I guess what this amounts to would be an initiation rite or a passage of ordeal, something we humans understand well enough? The benefits – if indeed the status of the individual receives this instant boost – would obviously be improved access to food, which means that on her next birth the same female individual would have a better chance of success than she otherwise would have had.
It’s possible that, although researchers like East and Holecamp have done such detailed data-collection on the hierarchy of the spotted hyena, they have missed this ‘kick up the ladder’, either because they had no search-image for it or because it was too subtle to be shown in their statistics?
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4069199/
(writing in progress)
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