29 de mayo de 2022

Did authentic mega-killers keep their mouths shut?

(writing in progress)

The extinct Smilodon, largest of all sabretooth cats, belongs to an extinct subfamily, Machairodontinae, of the family Felidae.

Smilodon is particularly well-known because of the unusually large number of skeletons excavated. More than 1200 specimens have been recovered at the La Brea Tar Pits of California, where the species is Smilodon fatalis.

The South American species Smilodon populator (https://prehistoric-fauna.com/Smilodon-populator-family and https://prehistoric-fauna.com/Smilodon-populator and https://prehistoric-fauna.com/Smilodon-populator-2008 and https://prehistoric-fauna.com/Smilodon-populator-family and https://prehistoric-fauna.com/Smilodon-populator-rec), largest of all recorded felids, is also fairly well-documented in terms of its skeleton.

This genus has repeatedly been depicted fang-baring in a way similar to the leopard (Panthera pardus, https://www.agefotostock.com/age/en/details-photo/snarling-leopard-with-huge-teeth/ESY-017555797) but with the mouth even more widely open. Although some artistic reconstructions of Smilodon may be unrealistic in other respects, a snarling expression in confrontation with other species may seem in line with all the known facts.

However:

Fang-baring varies greatly in extant Carnivora. For example, some families, such as the bears (Ursidae), show no fang-baring expressions in interspecific conflict, although the brown bear (Ursus arctos) does fang-bare in intraspecific confrontations. And even within the family Felidae, certain species (e.g. the caracal Caracal caracal) fang-bare extremely readily, whereas others (e.g. the Canada lynx Lynx canadensis) of similar body size and canine length fang-bare in interspecific conflict extremely reluctantly.

In the case of sabretooth cats in the genus Smilodon, there are three main reasons to doubt that fang-baring occurred at all, let alone in warnings to other species.

Firstly, it is unlikely that the canines were used in self-defence against other predators. The extremely large Smilodon populator of South America was more powerful than any sympatric predator and would have little to fear from attack by other Carnivora. However, Smilodon fatalis in North America coexisted with large species of wolves and bears which could potentially kill sabretooth cats.

This is because these teeth were extremely specialised for killing large herbivores, thought to be mainly megaherbivores
and would have been too cumbersome as well as too fragile to be used for rapid snapping or stabbing, or other methods of sparring. Indeed these teeth were probably a liability rather than an asset in brawling.

Secondly, the main weapons used by Smilodon, in fights with conspecifics and other Carnivora, were probably the self-sharpening claws, which were extremely large on the forefeet. The protractile claws of Smilodon were typical of the Felidae despite their exceptional size.

And thirdly, the function of fang-baring in felids is to show the full length and sharpness of the canines, which, in all extant Carnivora, are hidden by the upper lips when the mouth is in a relaxed expression

Because the canines projected permanently from the lips in sabretooth cats, such display seems pointless whether directed intra- or interspecifically. The depiction of fang-baring in most reconstructions of Smilodon is consequently a pseudo-scientific and superfluous bid for emotional appeal. Why would a felid flaunt the obvious?

In future, would I not be more realistic – and ultimately no less dramatic – to portray Smilodon keeping its mouth closed in aggressive and defensive postures?   

(writing in progress)

Ingresado el 29 de mayo de 2022 por milewski milewski | 0 comentarios | Deja un comentario

bustard

(writing in progress)

The Australian bustard (Ardeotis australis) is noteworthy because it is the largest species of flying bird in Australia. The mature male can reach about 14 kg, which is severalfold heavier than most species of eagles.

It also has a remarkable display in the male during the breeding season, in which the appearance is transformed by the inflation of several air sacs and the ‘flagging’ of several aspects of the plumage. During the early settlement of Australia, the Australian bustard was widespread and common enough to have been a sought-after item of food. Its flesh is tasty and not as tough as might be expected for a bird which spends its life walking as it forages.

However, it is only when one thinks laterally that the puzzling aspects of the Australian bustard emerge.

Firstly, it is a surprising fact that similar bustards (formerly regarded as conspecific) occur also in India, Arabia, and widely in Africa. This defies the usual pattern in which the Australian avifauna (other than aquatic or wetland-associated forms, plus certain raptors) is rather distinctive owing to the isolation of this continent. In the case of the largest bustards it is as if God said ‘the isolation of Australia be damned, I’m going to put the same bustard down on the African continent, the Indian subcontinent, and the Australian continent’.

Secondly, one of the most interesting and overlooked aspects of the Australian bustard (and its close relatives) is the extreme sexual dimorphism. Why so dimorphic in body size, without much difference in body shape? (For example, neither ostriches nor emus are particularly sexually dimorphic in body size).

And thirdly, associated with the great sexual dimorphism is the secretiveness of the female, in contrast to the conspicuousness of the male. Most photos of large bustards show the mature male, which tends to walk in the open. The female, being smaller, tends to hide (crouching down when disturbed), and i
I get the impression that it seldom photographed). It is as if the female is not even missed by photographers; nobody seems to notice that they are not spotting or photographing the female, and so certain surprising aspects of sexual dimorphism remain overlooked.

It occurs to me that, once one focuses on the female for a change, these large bustards may perhaps qualify for a certain kind of ‘record’ among birds.Who can think of a larger species of diurnal bird in which the colouration of the adult female is cryptic/disruptive? The general pattern among birds is that thoroughly inconspicuous (cryptic and/or disruptive) colouration tends to be restricted to nocturnal forms and, among diurnal forms, certain rather small birds of extremely open environments, such as larks, which can remain stationary and thus blend in to the surroundings. The large bustards, particularly in the form of the female, seem to be exceptional in this regard, not so?

One incidental point worth mentioning here is that large bustards lack a ‘blaze’ display on the tail when flying, in contrast to a general pattern among flying birds. The tail is inconspicuously marked and lacks dark or pale accentuation, so that when the tail is spread during take-off it does not become particularly conspicuous as in so many familiar birds including the domestic pigeon.

If I am right, then what would emerge is a realisation that the largest bustards are not not only the largest flying birds (as referring to the mature male). They are also the largest camouflage-coloured diurnal birds (as referring to the female). There is minimal sexual dimorphism in the colouration of female and male in normal postures, but the plumage and air-sacs are configured in such a way that the male – which tends to be more conspicuous anyway because of its large size – can transform itself into a virtual living ‘flag’ when displaying sexually. This ambivalence in large bustards, between remarkable inconspicuousness (female) and remarkable conspicuousness (displaying male) is, to my mind, one of the overlooked aspects of the biology of the Australian bustard.

I would like to know more about the subtle, oft-overlooked aspects of sexual difference in plumage between mature female and mature male in the Australian bustard, as well as its close relatives (Ardeotis kori, A. nigriceps, A. arabs). Most writers seem to have assumed that the sexes have similar colouration in their normal (non-diplaying) postures and actions, but I suspect that there are significant differences, along the lines I refer to in the captions below.

The following shows what I take to be adult female A. australis, and if I’m right then this is one of the few good photos of the female of the largest species of bustards. Note the relative downplaying of the dark markings, particularly at the base of the neck, and note the lack of tonal (pale/dark) contrast between wing-coverts and lower flanks/drumstick plumage. The ‘flank-panel’ (which actually occurs on the wing-coverts of the folded wing) is inconspicuous here owing to its ‘speckling’, whereas in mature males (particularly in the Indian species A. nigriceps) this panel can form a conspicuous dark band. The neck is not pale enough in this female to be conspicuous, and the dark marking on the crown also seems relatively subdued. I ask the question: is this the largest species of camouflage-marked diurnal bird in existence?

The following two photos show the mature male A. australis in breeding display. Not only are the markings somewhat bolder than in the female, but the inflation of several air-sacs, plus postural erections, transform what is otherwise a rather inconspicuously-coloured bird into a ‘living flag’.

(writing in progress)

Ingresado el 29 de mayo de 2022 por milewski milewski | 0 comentarios | Deja un comentario

28 de mayo de 2022

Surprising differences among the superficially similar large-bodied bustards

@rion_c @davidbygott @pelagicgraf @jacob12_ @jakob @johnnybirder @john8 @gumnut @joshuagsmith @ratite @dallonw @gatorhawk @subirshakya

The Australian bustard (Ardeotis australis, https://www.inaturalist.org/taxa/108-Ardeotis-australis and https://grasslands.ecolinc.vic.edu.au/fieldguide/fauna/australian-bustard#details) was once assumed to be conspecific with

The full extent of the differences between the Australian and African species have tended to be overlooked, partly because

The aim of this Post is to show clearly that

  • the Australian bustard and the kori bustard are more different than they may seem, and
  • the Australian bustard and the great Indian bustard are more similar than expected given their wide geographical separation.

DIFFERENCES BETWEEN THE AUSTRALIAN AND AFRICAN SPECIES

A reason why several differences have been overlooked is that they are hidden in the tail and in improbably distensible ‘air-sacs’.

The tail is obscured in the normal postures of both sexes of large-bodied bustards. Even in flight, the folded tails look deceptively similar between the Australian bustard and the kori bustard. It is only once the tail is variously raised in sexual, defensive and aggressive excitement that the caudal plumage shows the real differences in birds seen on the ground.

The ‘air-sacs’ lack any outer indications until spectacularly inflated in masculine displays. When the males of large-bodied bustards display sexually, they adopt extreme postures while ‘unfolding’ dark-versus-pale plumage in such outlandish ways that the normally inconspicuous birds are transformed into ‘living flags’. It is only then that the true differences in 'air-sacs' between the species become apparent in the extraordinary distended necks.

The tail is less noticeable in the Australian than in the African species, because:

  • in the Australian bustard, the retrices (stiff tail feathers) are relatively short and plain, whereas
  • in the kori bustard these feathers differ by being longer with pale barring which shows up when the tail is raised and fanned vertically or sideways (see https://www.youtube.com/watch?v=DYZgaYkyVKY ).

Furthermore,

  • in the Australian bustard, the white under-tail coverts and vent plumes remain oddly hidden in the masculine display, whereas
  • in the kori bustard, all these white feathers are fully exposed in any display of the tail.

Although there are no breeding plumages in the usual seasonal sense, the extending, erecting and inflating of complex and usually hidden surfaces and structures makes these normally unobtrusive birds into virtual beacons. And it takes hardly more than a glance to see that these masculine displays are surprisingly different between the Australian and African species.

In the Australian bustard, displaying males inflate what is thought to be the oesophagus to form their main ‘balloon’. This shape-shift enormously distends the skin of the lower neck into a conspicuously pale, pendulous 'stocking', which nearly trails on the ground as it swings (see https://www.youtube.com/watch?v=f5YJYmRt3Aw and https://www.youtube.com/watch?v=l9uoUcW-Yds ). This structure is absent in the kori bustard.

Additionally, males of the Australian bustard inflate air-sacs in the whitish upper neck. The kori bustard likewise inflates the greyish upper neck to show whitish, but in its case the distensions on left and right remain distinct, and the show is accentuated by a dark ‘chin’ (or, more precisely, crook-of-throat).

An adjunct display in the Australian bustard is that of the white feathers of the flank, which are spread to overlap the edge of the folded wing. This too is absent in the kori bustard.

In both species, displaying males raise the tail until its tip touches the neck, enhancing the dark-pale contrast.

However, the erect tail of the Australian bustard looks mainly brown in this display, whereas that of the kori bustard looks mainly white. Furthermore, the Australian bustard keeps its body horizontal while the tail is erect, whereas the kori bustard eventually swings its body into an almost vertical position.

The masculine display of the kori bustard is also more complex in its sequence of different postures, as follows.

First the male erects its tail to show its fluffy white underside, with drooped wings (see https://www.youtube.com/watch?v=KXjppefiMiU and https://www.youtube.com/watch?v=ITijczBTMLc and https://www.youtube.com/watch?v=233NDsLxWE4 ) not seen in the Australian bustard. It then erects its torso while further inflating the upper neck. Finally the tail-tip is lowered to the ground and the display culminates in the male standing vertically to emphasise the fully-ballooned neck at maximum height (see https://www.youtube.com/watch?v=WloXywNfxOE and https://www.youtube.com/watch?v=wC3ADdhCZag) – a posture not seen in the Australian bustard.

The only displays shared by males and females in these bustards seem to be those of the tails in non-sexual contexts. In both sexes while on the ground, certain postures can bluff antagonists by making the whole body seem larger than it really is. The tail is fanned in various ways while the wings are spread to impress rather than to fly.

The kori bustard has been photographed more frequently performing these bluffing displays. Perhaps this is because its habitat differs from that of the Australian bustard. The kori bustard shuns tropical woodlands and prefers the exposure of semi-deserts - where a typically African array of herbivores and predators occurs despite the limitations of seasonal drought.

The difference between the habitats of the two species means that the kori bustard interacts more frequently with other large animals than does the Australian bustard (e.g. see https://www.traveller24.com/Explore/Bush/watch-secretary-and-kori-bustard-in-bird-brawl-unlike-anything-youve-seen-in-kruger-20190423 and https://www.mikerae.com/birds-living-at-ndutu/kori-bustard-being-badly-hunted-ardeotis-kori/ and https://www.louwphotography.com/Africa/Tanzania/Ngorongoro-Crater/i-Qd5hTGJ/A and scroll in https://douganddaniele.tumblr.com/post/28046046332/safari-101-on-the-wing and 'kori bustard and tawny eagle tangle over termites' in http://www.eyesonafrica.net/updates/2010/upd_jan10-1.htm).

Bustards are furtive compared with storks, cranes and the secretary bird (Sagittarius serpentarius). However, there are times when even females hold their ground while spreading the tail and wings in bluff, whether defensively or offensively; there are threats to eggs and juveniles from trampling herbivores and sundry predators. Spectacular examples are attacks by the martial eagle (Polemaetus bellicosus) (see https://www.facebook.com/biopicsbyjudylehmberg/posts/martial-eagle-killing-a-kori-bustardwe-have-been-lucky-enough-to-spend-a-good-bi/1548749875365018/), a bird-eating raptor with no precise counterpart in Australasia.

When the kori bustard displays in these non-sexual contexts, it fans the tail vertically without spreading its wings (see https://www.youtube.com/watch?v=rB2Fz8kvh6s ) or laterally while spreading its wings (see https://www.alamy.com/kori-bustard-fighting-springbok-image2337624.html ).

The kori bustard sometimes competes with vultures for carrion (https://angama.com/blog-posts/this-week-at-angama/this-week-at-angama-50/). There is even a record of this species performing its bluff while contesting with the southern pale chanting goshawk (Melierax canorus) for prey flushed incidentally by the honey badger (Mellivora capensis). This is a daring example of self-assertion given the reputation of this carnivore (see https://www.sciencephoto.com/media/561323/view/pale-chanting-goshawk-and-kori-bustard and https://fineartamerica.com/featured/kori-bustard-with-pale-chanting-goshawks-tony-camacho.html).

The two subspecies of the kori bustard are widely disjunct within Africa. The following show that the appearance remains similar despite the wide geographical gap:

Southern Africa subspecies, Ardeotis kori kori: http://www.stellenboschbirds.com/gompou.html

East African subspecies, Ardeotis kori struthiunculus: https://www.africanbirdclub.org/afbid/search/birddetails/species/455/4661

SIMILARITY BETWEEN THE AUSTRALIAN AND ASIAN SPECIES

In males, the pale parts of the body tend to be noticeably paler, while the dark parts tend to be noticeably darker, in the great Indian bustard than in the Australian bustard.

The result is that the great Indian bustard has bolder colouration and is the more conspicuous species, whether displaying or not.

However, the females remain so similar that taxonomists might legitimately ‘lump’ the Australian and Indian forms as two subspecies of a single species, were they not so disjunct geographically. This presents a biogeographical puzzle: much similarity has persisted despite the wide sea-barrier of six thousand kilometres.

This close relatedness is particularly revealed by a little-known tract of plumage, as follows.

When the tail is raised in masculine displays, an adjunct whorl of feathers on each side (left and right) - which has yet to be identified anatomically but may correspond to the femoral tract - is also erected in such a way as to cover most of the white under-tail coverts with a brown fan. No such tract of plumage plays any role in the displays of the kori bustard. This categorical difference leaves the Indian and Australian forms in close alliance.

The following photos show masculine display in the Australian bustard. Please note what looks like a brown fan of feathers on the side of the tail: http://www.raywilsonbirdphotography.co.uk/Galleries/Birds/Regions/Australasia/Aus_Australian_Bustard.html and https://www.mindenpictures.com/stock-photo-australian-bustard-ardeotis-australis-male-displaying-victoria-naturephotography-image00415250.html and https://steve-wilson.smugmug.com/Australian-birds/ and https://www.alamy.com/stock-photo-australian-bustard-ardeotis-australis-adult-male-calling-during-courtship-70267954.html and https://www.agefotostock.com/age/en/details-photo/australian-bustard-ardeotis-australis-male-in-courtship-display/U53-601149 and https://www.youtube.com/watch?v=THY4fDU0PPg and https://www.mdahlem.net/birds/7/bustard.php.

Partly in review of the various lines of information presented above, here are photos showing the consecutive stages of masculine display in the kori bustard:

Ardeotis kori struthiunculus, male, in initial stage of sexual display:
https://www.shutterstock.com/es/video/clip-1009864109-kori-bustard-ardeotis-walking-around-on-serengeti

Ardeotis kori struthiunculus, male, with tail fully erected in sexual display:
https://africanbirdclub.org/afbid/search/birddetails/birder/455/23012

Ardeotis kori struthiunculus, male, with air-sacs in the upper neck fully inflated in sexual display:
http://www.stellenboschbirds.com/gompou.html

Ardeotis kori struthiunculus, male, culmination of sexual display with torso fully upright and tail lowered:
https://www.mindenpictures.com/search/preview/kori-bustard-ardeotis-kori-male-displaying-masai-mara-game-reserve-kenya/0_90748197.html

Kori bustard, Ardeotis kori struthiunculus, male, culmination of sexual display with torso fully upright and tail lowered:

Ingresado el 28 de mayo de 2022 por milewski milewski | 1 comentario | Deja un comentario

A hyperconspicuous horse, hiding in plain sight

@pelagicgraf @simontonge @maxallen @aguilita @jwidness @bobby23 @johnnybirder @oviscanadensis_connerties @tandala @artois @sciencegirl02 @saber_animal @woodridgejeff @rlawrenz

Much has been written about the narrow escape from extinction by the takhi (Equus przewalskii, https://en.wikipedia.org/wiki/Przewalski%27s_horse), the last form of wild horse on Earth. However, the adaptive colouration of this species has not previously been discussed.

Just as the striping of zebras is puzzling, so the hyperconspicuousness of the takhi is puzzling. The difference is that the former puzzle is popular, whereas the latter puzzle is unacknowledged.

The colouration of the takhi makes it conspicuous at all ages and in all seasons. It gleams out from the treeless grasslands during the sunny time of year (https://www.inaturalist.org/observations/32959824 and https://www.inaturalist.org/observations/108162555). Why would a large ungulate advertise itself to this degree to its predators, such as wolves?

Particularly puzzling is the fact that infants of the takhi are both extremely pale for Equus and far paler than adults of the species. Note that, in infants,

In this complex pattern of depigmentation and sheen in infants, the takhi is extreme among all the species and subspecies of Equus.

Now, it is one thing for large animals, living in open environments, to have colouration making the adults even more obvious to predators than they already are. It is another for infants – which are precocial in all equids including the takhi - to adopt this showiness from the start. And it is something else again for the conspicuous colouration of infants to be additionally configured, as opposed to being merely precocial.

Inasmuch as it self-advertises at several ontological levels, the takhi can perhaps be characterised as a hyperconspicuous ungulate.

In order to understand the adaptive value of the particular conspicuousness of the takhi, let us first review the colouration of the infants of comparable wild ungulates.

In Equus there are three patterns in the colouration of infants relative to adults.

Firstly, the colouration is similar to that of adults right from birth in zebras and African asses – none of which is as self-advertising in its colouration as the takhi. In these forms, infants show nearly adult colouration, partly because the mane is fully developed from the start (https://www.alamy.com/zebra-mother-and-baby-zebra-running-side-by-side-on-grass-in-masai-mara-kenya-image362235495.html).

Secondly, in Asiatic wild asses the infants resemble adults but are not quite as self-advertising because the mane – conspicuously dark even if short in adulthood – remains poorly developed at birth.

In the following species, infants are almost as pale as those of the takhi, the difference being that adults lack the dark contrasts conferred in the takhi by the lower legs, substantial mane, and broad tail-tassel:

And thirdly, we have the takhi with its characteristic pallour, as described above.

Among large, gregarious ruminants with habitats resembling those of Equus, the general pattern is for infants to have disruptive (camouflage) or cryptic (plain) colouration regardless of the adult colouration. Even in habitats with vegetation too low or sparse to conceal adults, the infants hide in the environment, usually by lying flat apart from the herd for most of the day and night, for several weeks.

For example, in the wapiti (Cervus canadensis), a species of large deer partly sympatric with the takhi in Mongolia, the colouration of infants is spotted for camouflage (https://www.gettyimages.co.uk/detail/photo/wild-baby-elk-or-wapiti-in-green-grass-royalty-free-image/657484904 and https://www.leesonphoto.com/image/I000081bIE2S5edQ).

In most large African antelopes, the colouration of infants is a medium fawn, plain and not particularly pale, which confers inconspicuousness provided the infants lie stationary. Even hartebeests (Alcelaphus, https://videohive.net/item/red-hartebeest-and-suckling-calf/21285845 and https://www.dreamstime.com/stock-image-baby-red-hartebeest-antelope-image13753251 and https://www.dreamstime.com/stock-image-red-hartebeest-image779081), which are exceptionally fast and enduring runners, retain the usual pattern in which infants hide rather than joining the group.

No form of horse, ass or zebra conforms to the typical pattern of ruminants, because the infants of Equus are so precocial that they are active immediately after birth, remain with the herd from the start, and are as apparent as their parents. But why has the takhi evolved to be conspicuous?

One approach to this puzzle may be to focus on the prime examples of infantile conspicuousness among ruminants, namely certain wildebeests (Connochaetes) of Africa.

Wildebeests are

  • the only ruminants which emulate Equus in having newborns so precocial that they can keep up from the start with adults fleeing at maximum speed from predators,
  • the most specialised of ruminants for long-range seasonal migration,
  • more synchronous in their breeding than expected, considering their year-round territoriality in tropical climates.

In addition to their extreme precociality, certain species of wildebeests qualify are conspicuous as follows (see https://www.inaturalist.org/posts/54094-adaptive-colouration-in-wildebeests-part-1-large-scale-conspicuous-features#):

  • adults have particularly bold patterns by virtue of gross combinations of dark and pale (although the configurations of contrast differ from that seen in the takhi),
  • infants are self-advertising by virtue of their overall paleness, and
  • the fawn colour of infants differs from a cryptic plainness because it contrasts with the precocially dark face.

In both the takhi and wildebeests, then, there is a combination of

  • infantile paleness,
  • adult conspicuousness owing to dark-pale contrasts,
  • sheen/antisheen at all ages,
  • immediate integration of infants into the group, and
  • extremely seasonal breeding.

In ruminants, conspicuous colouration is often associated with self-advertisement to predators, based on the principle that

  • gregarious species living in the open tend to be conspicuous even if plain-coloured, and
  • those individuals proving their fitness by 'stotting' are unlikely to be targeted for pursuit by predators scanning the group.

‘Stotting’ in wildebeests is subtle and complex. Adults react to the approach of potential predators by cavorting or style-trotting (https://www.shutterstock.com/nb/video/clip-5778965-cavorting-animal-mad and https://whyevolutionistrue.com/wp-content/uploads/2021/06/download-1-1.png), as if amused and exhilarated by the menace. Infants of wildebeests run in particularly bouncy ways on such occasions, as if playing.

It seems to make sense that if the best way to avoid being targeted is to show off to potential predators, then self-advertising colouration enhances this strategy. But, returning to equids: the trouble is that nobody has ever observed the takhi ‘stotting’, even in infancy.

The question of why zebras are striped has produced several potential explanations, which continue to be tested; the puzzle has fully gripped the imagination of biologists. The takhi poses a parallel puzzle, because its appearance is equally counterintuitive in its own way. However, in its case the question has, until now, been overlooked.

FURTHER ILLUSTRATIONS:

The following shows the distinctive pallour of the newborn takhi, a pattern transcending that in any species of ass or zebra. Despite being at home in well-watered lands, the takhi starts life paler than any other species in the genus Equus and as pale as the most arid-adapted large antelope, namely the addax (Addax nasomaculatus) of the Sahara.
Equus przewalskii:
http://www.zooborns.com/.a/6a010535647bf3970b01b8d28b14be970c-800wi

The following shows that the pallour of infants of the takhi results partly from the initially poor development of the dark markings on the legs (note the trace of striping on the fore leg of this individual infant). The mane, although showing the first signs of dark bristles, is also poorly developed relative to the newborns of other forms of Equus.
Equus przewalskii:
http://www.zooborns.com/.a/6a010535647bf3970b019aff57687f970c-800wi

The following shows that sheen contributes to the conspicuousness of infants of the takhi. Several features make adults of the takhi obvious to the human eye even at distances of more than a kilometre. Firstly, the pale ventral surface of the torso is extended so high on the flank that it catches the light; this pale area exhibits sheen in the summer coat. Secondly, the muzzle is conspicuously pale. Thirdly, the lower legs, mane and tail-tassel are conspicuously dark. The colouration is similar between seasons except that the sheen seems to be restricted to the summer coat.
Equus przewalskii:
http://www.zooborns.com/.a/6a010535647bf3970b019aff57c5f3970d-800wi

The following shows that adults of the takhi are conspicuous even in snow by virtue of the darkness of the mane, tail and lower legs. The pallour of infants might hypothetically hide them in such backgrounds, but the seasonal demands of reproduction tend to preclude births in winter.
Equus przewalskii:
https://www.unicorntrails.com/files/galleries/ride633_9042

The following shows that in the western white-bearded wildebeest as in the takhi, infants are pale in contrast to the large-scale contrasts between pale (mainly owing to sheen) and dark in adults. Also note the precocial locomotion.
Connochaetes mearnsi:
http://l7.alamy.com/zooms/f8cf41d4e932430d865f20addbc8f3e6/blue-wildebeest-connochaetes-taurinus-with-newborn-calf-serengeti-gac3pw.jpg

The following shows the sheen on the legs, and a precocially dark face, in infants of the western white-bearded wildebeest; these are consistent with the fact that the infants of wildebeests lack hiding behaviour by day or, as far as we know, by night.
Connochaetes mearnsi:
http://c8.alamy.com/comp/GA3CW6/blue-wildebeest-with-newborn-calf-connochaetes-taurinus-serengeti-GA3CW6.jpg

The following shows that the western white-bearded wildebeest is born as pale as the ‘white’ beard of adults, consistent with the adaptive conspicuousness of infants.
Connochaetes mearnsi:
https://static.greatbigcanvas.com/images/singlecanvas_thick_none/panoramic-images/newborn-wildebeest-calf-running-with-its-mother-ndutu-ngorongoro-tanzania,119306.jpg?mw=540&mh=380&max=540

The following shows that infants of the Indian wild ass are almost as pale as those of the takhi. However, this paleness is not anomalous relative to adults, the dark mane of which is shorter and thus less noticeable than in the takhi. Asiatic wild asses, although conspicuous, do not qualify as hyperconspicuous because the colouration of infants is precocial rather than ontogenetically distinctive.
Equus khur:
https://i.pinimg.com/736x/6e/66/4f/6e664f5017de6d14c71888c0a7330427--iran-persian.jpg

The following shows that the dark mane and tail-tassel have yet to develop in infants of the Tibetan wild ass. However, infants of this species are not as pale as those of the other forms of wild asses.
Equus kiang:
https://i.pinimg.com/736x/61/71/c1/6171c1e2d72b500a671ff2d9a81ee0b1--baby-horses-asia.jpg

The following shows that the Somali wild ass differs from the takhi in that its infants are not particularly pale, and differs from Asiatic wild asses in that its mane is so precocial that it has developed by the time of birth.
Equus somaliensis:
http://www.zooborns.com/.a/6a010535647bf3970b019afff07af2970d-800wi

The following shows that in the plains zebra infants can be as intensely marked as adults.
Equus quagga boehmi:
http://visionsofnature.biz/uploads/processed/0029/0610171111111zebra_and_foal__serengeti.jpg

The following shows that mountain zebras resemble the plains zebra in the relationship of infants to adults in colouration.
Equus zebra:
https://i.pinimg.com/736x/3f/28/e2/3f28e28f73cbb79425043aa2df4bd632--zebra-pictures-animal-pictures.jpg

The following shows that Grevy’s zebra, although having the narrowest striping among zebras, likewise has infants striped much like adults.
Equus grevyi:
http://l7.alamy.com/zooms/5466eca17fc24da9b9f35eafe61104a2/grevys-zebra-equus-grevyi-adult-female-and-foal-standing-in-semi-desert-f7xe9e.jpg

Ingresado el 28 de mayo de 2022 por milewski milewski | 5 comentarios | Deja un comentario

27 de mayo de 2022

The peniform clitoris of the spotted hyena, reconsidered

(writing in progress)

Everyone knows that the spotted hyena (Crocuta crocuta, https://en.wikipedia.org/wiki/Spotted_hyena) is odd in having a peniform clitoris.

The usual interpretation is that this allows females to emulate masculinity in a society that is matriarchal to an unusual degree among mammals. Or, more particularly, that females have converged with males by having extremely modified genitalia. In various publications the view is taken that the spotted hyena shows ‘sexual monomorphism’ (https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0310.1986.tb00570.x#:~:text=Abstract,clitoris%20closely%20resembling%20a%20penis and https://www.researchgate.net/publication/230213058_Sexual_Monomorphism_in_Spotted_Hyenas_Crocuta_crocuta) and that the peniform clitoris of the female ‘mimics’ the penis.

However, let us rethink the whole conceptual framework.

The conventional view - which I question in this Post - can be elaborated as follows:

  • The female genitalia are similar to those of the male, including a peniform clitoris which looks so similar to a penis that the sexes are hard to distinguish.
  • Clitoral greetings are particularly important for maintaining a strict hierarchy, in which females tend to dominate males.
  • The erect peniform clitoris is used in greetings between individuals, during which olfactory signals are exchanged.
  • The size and scent of the peniform clitoris provide an honest form of communication between individuals.
  • The need for females to dominate males in competition for food arises from the unique strategy of the spotted hyena in travelling for up to five days away from the den on foraging excursions, to generate and then bring back milk to the young.
  • 'Sexual mimicry' (https://dash.harvard.edu/bitstream/handle/1/41467428/113481%20muller.pdf;jsessionid=3AA952CD2804CE17C8AAD0C7CC130F3D?sequence=1 and https://sciencetrio.wordpress.com/2009/11/09/genital-mimicry-social-erections-and-spotted-hyenas/) in the spotted hyena is thus partly explained by the idea that successful breeding depends - more than in any other mammal - on full dominance of females over all males, and maintenance of the female hierarchy across a clan which can be extensively dispersed.

However, this account throws up several incongruities. 

Females display the peniform clitoris not to males (which have their own separate hierarchy) but to females. It is the subordinate, not the dominant, individual that tends to show an erection in greeting rituals. In juveniles of the spotted hyenas, the clitoris is larger (relative to body size) than in adults. Only in the spotted hyena does the clitoris double as a birth canal; this species actually gives birth through its clitoris. (An enlarged clitoris per se is not unique to the spotted hyena, occurring also in e.g. true moles (Talpidae, https://en.wikipedia.org/wiki/Talpidae) and the fossa (Cryptoprocta ferox, https://en.wikipedia.org/wiki/Fossa_(animal)). And in other ways as well, the peniform clitoris is not actually analogous to the penis.

These incongruities suggest that a central question about this species is not why the clitoris is so penis-like, but why the birth-canal has been relocated to pass through an organ as narrow as a penis. Please note that the clitoris could theoretically have been just as penis-like but separate from the vagina, with only the urethra running through the clitoris.

What I have not seen pointed out previously is that it has - in evolutionary terms - always been possible for the peniform clitoris of the spotted hyena to contain the urethra (and thus to be the route for micturition, just like the penis) without also serving as a birth-canal. After all, in most mammals the urethra and the vagina are separate in the first place. So the spotted hyena has chosen, evolutionarily, not only to fuse the the urethra with the clitoris, but also to fuse the vagina with the clitoris. These are two different changes, and the more puzzling one is the fusion of the birth canal with a penis-like tube because this makes birth so difficult. The risks are potentially lethal.
  
The penis is mainly an organ of masculine intromission, but the peniform clitoris is - I hypothesise - mainly an organ of demotion.

Please consider that, In the spotted hyena, there are two ‘bottlenecks’ of life-and-death importance in the groin of the female.

Firstly and most importantly, there is a metaphorical bottleneck of the milk supply to offspring. The whole life-history strategy of the species depends on milk flowing at a certain rate and timing for reproduction to succeed. Let us assume for now that a crucial aspect of the spotted hyena is how odd the lactational bottleneck is in breeding females.

The second bottleneck is that of the birth canal, which has been converted into the narrowest form conceivable. This more literal bottleneck means that both birth and growth have been so configured as bottlenecks.

These bottlenecks may ensure that  the most proficient individual females reproduce successfully with the resources acquired by the whole clan. Crucial here is that the milk supplied by the dominant females exceeds what it would be if the spotted hyena foraged as a solitary animal. The collective procures much of the food (by gregarious hunting and by gregariously overpowering the lion) but a few individuals channel much of this food through their bodies.

The security of the milk in the female's udder is of paramount importance. Production of milk over five days of exertion, by virtue of access to food in an extremely competitive species, is likely to be vital for survival of young. The peniform organ is an instrument whereby inferior/lower-ranking females reaffirm their place unequivocally. This increases the security of the milk because it largely removes the risk of a milk-bearing female being challenged and injured, or prevented from eating, by other females of the clan. This rationale also invokes larger predatory species; the spotted hyena needs to have unquestioned access to the kill but it also needs conspecific help in its contests with the lion (Panthera leo). This is why the collective of the clan is so important and it is crucial that all members know their place in it.
  
We can accept that the peniform clitoris is an honest organ in the spotted hyena, preventing any miscommunication or political pretences that could put the most valuable members of the clan, namely the dominant milk-bearing females, at risk. There is a premium on olfactory truthfulness in this species, revealing the true political alliances, because the complex alliances cannot be observed in real time, and must be observed virtually instead. The peniform clitoris hypothetically ensures that there is minimal deception given that a given individual of the spotted hyena is unable to see most of the interactions among other individuals in the way possible in e.g. baboons (Papio). Honesty is crucial because the spotted hyena has a ‘virtual’ clan rather than one in which political machinations can be observed in real time.
 
What, then, is the true main function of the peniform clitoris of the spotted hyena? My goal here is to label this ‘an organ of ....’ along the lines of calling the penis ‘an organ of sexual intromission’. I suggest that the answer is 'social demotion' (as opposed to promotion).
 
The reason why this is worth careful consideration is that no other animal seems to possess an organ of demotion, and demotion is something different from submission in the sense of surrender. Besides, submission already has a particular social meaning in Biology.
 
Submission needs no special organ because all the animal has to do is lower its head or its ears, put its tail between its legs, whimper, or lie with its belly exposed. Submission means ‘giving up’ in the context of a particular agonistic event. What happens in the spotted hyena is different: it is indeed submission in the sense that the individual submits to a process in which it is usually 'humiliated' (the process being the detailed olfactory examination of its peniform clitoris). However, submission describes this poorly because surrender takes only a moment whereas what really happens in the greeting ceremony of the spotted hyena is more like an interrogation.
 
'Sexual monomorphism’ is misleading in the spotted hyena because the peniform clitoris and the normal mammalian penis are functional opposites, in the following sense. The penis is always erected and displayed in a context of promotion, i.e. the male individual promotes himself socially and/or sexually. No male animal except the spotted hyena, as far as I know, erects its penis to ‘submit’ to any other individual, or to be 'humiliated'. The penis is mainly a sex organ but in its social use it is promotive, implying superiority where there is rivalry among males.
 
A crucial aspect of the spotted hyena, not reflected in the conventional view, is that the relationship has been inverted. The peniform organ is now erected demotively rather than promotively. Female in erection affirm their demotion, and this has perhaps extended partly to males, which may experience erection not merely in sexual excitement or self-assertion vs other males, but also as a way of affirming ‘I remain demoted’ to a courted female.
 
It is by this rationale that I suggest that we regard the peniform clitoris of the spotted hyena as ‘an organ of demotion’.
 
Come to think of it: does the spotted hyena erect its peniform organ while micturating?
 
Given that in both male and female of this species the peniform organ serves as a spout for urine, and given that in flaccid mode the peniform organ is little more than a bump on the surface of the body, it is easy to assume that the act of micturition – even if only for reasons of hygiene – would involve the partial erection of the peniform organ. And this may indeed be a reasonable assumption in the male.

However, we know that, in the case of female, there is no ceremonial micturition; urine is passed urine without ritual, often while lying down, soiling the fur of the flanks. This leads me to doubt that females bother to erect the clitoris, even partially. This, if true, would be important because it shows that the peniform clitoris hardly qualifies as a functional spout for urine. It is not really convergent with the penis in this function, if the female does not actually convert her flaccid clitoris into a spout while micturating.
  
The problem with the terms 'sexual mimicry' and 'sexual monomorphism':

Mimicry is essentially functional, i.e. the object concerned gets an advantage from resembling the object that it resembles. By mimicking a toxic butterfly, a harmless butterfly implies a functional similarity, in this case toxicity (which is untrue). This correct use of ‘mimicry’ surely does not apply to the spotted hyena. If it were a case of mimicry, then we would expect that the peniform clitoris would behave like a penis.

The only functional similarity is that the clitoris produces scent, much as the penis does - which is not enough evidence of overall mimicry. Besides, it seems tenuous to claim that the organ needs to resemble a penis physically to produce the scents in question. The vulva of the normal female mammal is perfectly capable of giving off scents. So even here the case for mimicry seems weak.

'Monomorphism' is too easily misinterpreted (the more insidiously for the fact that this is usually implicit rather than explicit) to mean that the genitalia of the female are like those of the male. I think the truer interpretation of the same facts is that what is most remarkable is how functionally different these female genitalia are from normal mammalian male genitalia.

If the peniform clitoris were really to resemble the penis functionally, the following would apply.
 
Firstly, the clitoris would be used for penetration. This is conceivable if one imagines that in the spotted hyena there might have been a matriarchal system in which a female ritual of dominance consisted of rape-like actions. It is interesting that there seems to be no recorded instance of female-on-female rape in the animal world, but if such a thing was possible it would surely be in a species with a peniform clitoris. Even anal rape is conceivable in the spotted hyena given that this species lacks a vagina in the conventional sense.
 
Because nothing of the sort occurs in the spotted hyena, the concept of mimicry does not seem apt. As far as I know, females do not even mount subordinate individuals ritually, as happens in e.g. certain ruminants.
 
Secondly, the clitoris would be used as a spout for urine, particularly in scent-marking (as seen in the domestic dog). As far as I know, there is no mimicry of the penis w.r.t. micturition, other than the fact that the urine exits from the peniform organ (I suspect usually in its most flaccid state).
 
Thirdly, the clitoris would be used in the body language of self-assertion or the display of confidence/libido. This is seen in primates including humans, signified by the slang word ‘cock’ and ‘cocky’. In fact there is nothing ‘cocky’ about erection of the peniform clitoris. Instead its erection being a particularly clear signal of self-demotion rather than self-promotion.
 
So, could it be that this puzzle, i.e. that the clitoris of females superficially resembles the penis of males while not mimicking it functionally, that is central in our understanding of the species as a whole?
  
And is the fact that the spotted hyena gives birth through its clitoris not, in a sense, proof of a lack of mimicry?

(writing in progress)

Ingresado el 27 de mayo de 2022 por milewski milewski | 12 comentarios | Deja un comentario

26 de mayo de 2022

Ecological notes on Syzygium (Myrtaceae) in southern Africa

@jeremygilmore Comments please?

One of the obvious biotic differences between southern Africa and Australia is in the incidence of Myrtaceae (https://en.wikipedia.org/wiki/Myrtaceae).

Myrtaceous trees and shrubs cover much of Australia across a wide range of climates and soils. By contrast, they tend to be few and far-between - and therefore easily overlooked - in southern Africa.

A main ecological difference between these continents is the extreme nutrient-poverty of Australia, together with a limited incidence of herbivores and an extreme incidence of wildfires.

This raises the question:
How do the indigenous Myrtaceae of southern Africa relate to poor soils, herbivores, and wildfire?

The following notes may begin to shed some light on this topic, focussing on syzygiums (https://en.wikipedia.org/wiki/Syzygium), a genus indigenous to both continents.

EASTERN SOUTH AFRICA (see https://upload.wikimedia.org/wikipedia/commons/a/ad/St_Lucia_Estuary_OSM.png)

The relevant myrtaceous tree species here are Syzygium cordatum (https://www.inaturalist.org/taxa/338719-Syzygium-cordatum) and Syzygium guineense (https://www.inaturalist.org/observations?taxon_id=132507). These have succulent fruits and are dispersed and sown by frugivores. In this way they differ from most fire-adapted Myrtaceae in Australia, as well as most woody plants adapted to poorly-drained ground worldwide.

Syzygium cordatum occurs in stunted form in the area of Lake Sibhayi (https://en.wikipedia.org/wiki/Lake_Sibhayi). This a nutrient-poor part of Amatongaland (https://en.wikipedia.org/wiki/Amatongaland and https://www.researchgate.net/figure/The-Mkuze-Wetland-System-showing-the-extent-of-the-floodplain-and-the-location-of_fig1_7139313).
 
According to Tinley K L (1976, The ecology of Tongaland), a main habitat of S. cordatum in this area is the level just above that of the lake edges, where the upper soil is not waterlogged although the subsoil probably is. In such situations S. cordatum is the only tree, growing with the grasses and sedges Urelytrum squarrosum, Bulbostylis contexta, Monocymbium ceresiiforme, Eragrostis sp., Imperata cylindrica, Mariscus sp., Andropogon sp., Ischaemum arcuatum, Eragrostis capensis and E. chapelieri, Perotis patens, and Dactyloctenium geminatum.
 
Another main habitat of S. cordatum is ‘woodland’ (which I take to be savanna). One variant is ‘umdoni veld’, in which S. cordatum shares the tree stratum with many other taxa, e.g. Strychnos spinosa and S. madagascariensis, Dichrostachys cinerea, Albizia adianthifolia, Mundulea sericea, Hyphaene natalensis, Brachylaena discolor, Sclerocarya caffra, Ziziphus mucronata, Trichilia emetica, Apodytes dimidiata, Ficus stuhlmannii, and Acacia nilotica ssp. kraussiana. “In the eastern section [of the Lake Sibhayi area] Syzygium cordatum is the dominant woodland species changing to Terminalia sericea in the west, where the latter is dominant. The central part of Sibayi has an overlap of both types of vegetation.”

Tinley notes that “This country is commonly used by hippos for grazing purposes”. Although nobody expects S. cordatum to be eaten by the hippopotamus (https://www.inaturalist.org/taxa/42149-Hippopotamus-amphibius), the habitat is surely affected by this megaherbivore in Amatongaland. This defies resemblance to Australia, where megaherbivores are absent.
 
Swamp forest (see https://en.wikipedia.org/wiki/Forests_of_KwaZulu-Natal) occurs in the Sibhayi area as in other parts of Amatongaland, where the water runs rather than remaining stagnant. The tallest trees are Ficus hippopotami, Macaranga capensis, Voacanga thouarsii, Morella serrata, and Halleria lucida, and the main plant near ground level is the scandent fern Stenochlaena tenuifolia. Syzygium cordatum occurs at the edge of this poorly-drained forest, not within it.
 
Syzygium cordatum also occurs at the edges of two other types of forest, namely coastal forest and dune forest, in the Sibhayi area (see https://en.wikipedia.org/wiki/Forests_of_KwaZulu-Natal; bushpig, bushbuck, cane rat, red duiker, and suni occur in both types, but the nyala is absent from dune forest.)

Syzygium cordatum is thus absent from vegetation that is free of wildfires (coastal and dune forest as well as swamp forest), or subjected to permanent inundation at the surface (swamp forest). On the other hand, it also seems to be excluded from considerable areas of grassland owing to wildfire and/or good drainage. Where the intermediate conditions suit it, it can be the most prominent species of tree in savanna.
 
In summary so far:
Although Tinley does not put it together this way, I infer that S. cordatum is widespread in the Sibhayi area of Amatongaland wherever there is a combination of

  • nutrient-poor soils,
  • enough grass to carry wildfire, and
  • some degree of waterlogging in the subsoil.

However, the hippopotamus is likely to be naturally present wherever S. cordatum is common in Amatongaland. This 'megaherbivory' tends to undermine any analogy with Australia.
  
Farther south, on the coastal plain near the Mkuze River:

On the western edge of Oyengo Pan is a small belt of trees of S. cordatum. On the coastal side is a plain of nutrient-poor whitish sand, characterised by 'lala palm' (Hyphaene) scattered in grassland. (In the same area, ‘in places small patches of bush occur on large ant-hills’). In this zone, S. cordatum occurs extensively along the edges of treeless marshes covered in graminoid vegetation. The trees of S. cordatum are 8-9 m high, and the only plants growing under them are grasses.

I infer that S. cordatum forms savanna here, withstanding wildfires without becoming stunted. However, S. cordatum also grows in the largely treeless grassland (characterised by Hyphaene and Phoenix) as a dwarf, as does Parinari curatellifolia (https://en.wikipedia.org/wiki/Parinari_curatellifolia).
  
The tallest vegetation (reaching 18 m high) in this coastal belt of the Mkuze area is swamp forest, occurring along the main drainage lines. Neither S. cordatum nor Syzygium guineense is mentioned as present.
 
Moving to the northwest, closer to the Lebombo hills on the western side of the Mkuze area, we find drainage lines such as the Ophanzi, where riparian forest (not to be confused with swamp forest) reaches 18 m high and includes S. guineense. Similar riparian forest, dominated by Ficus sycamorus, occurs along the Mkuze River itself.
 
It is apparent that both S. cordatum and S. guineense are associated with partly wet conditions. Riparian forest of Ficus sycamorus tends to be inundated in summer owing to overflow of rivers, but in winter the soil is well-drained. In the case of S. cordatum, the typical situation seems to be the edges of marshes, where there is permanent waterlogging of the subsoil. Although S. cordatum may be dwarfed by frequent wildfires, there does not seem to be any obvious relationship between the height of S. cordatum and either drainage or wildfire.
 
My conclusion so far:
In southeastern Amatongaland, S. cordatum forms a short (about 5 m high) savanna, in which it can be the main tree. This savanna seems to be fire-prone, implying that even trees of S. cordatum can withstand frequent wildfires under certain regimes. This fire-tolerance is unique for myrtaceous trees in southern Africa, and seems somewhat convergent with confamilials (not necessarily congeners) in Australia.

Syzygium cordatum seems to be well-adapted to savannas at the edges of marshes in Amatongaland, which are too nutrient-poor for other trees, too poorly-drained for tall trees in general, and subject to wildfire (albeit not to the exclusion of 'megaherbivory').

A complication is the ability of S. cordatum (in parallel with Parinari but with greater abundance) to adopt a dwarfed form in situations where all trees are excluded by whatever factor it is that excludes trees in the pale sandy belt of Amatongaland. Also deserving more thought is the parallel between this S. cordatum and two genera of palms (Hyphaene and Phoenix), which are likewise capable of growing into fairly large trees but are usually found in stunted form in Amatongaland.
 
MALAWI AND ZAMBIA

Syzygiums are prominent plants in the Malawi-Zambia area, contributing to catenas in miombo (https://en.wikipedia.org/wiki/Miombo) and locally dominant in a wide variety of growth-forms. The nutrient-poverty with which syzygiums are associated, and the extreme plasticity of forms, are noteworthy in any comparison of Myrtaceae in southern Africa and Australia.

Burtt Davy et al. (1958), on page 15, provides information about Syzygium mumbwaense (https://plants.jstor.org/compilation/Syzygium.mumbwaense; White (1962) seems to regard this as Syzygium guineense ssp. huillense, which is confusing) in miombo in Malawi. I infer that

  • its habitat, being sandy and nutrient-poor, resembles Australia,
  • other nutrient-poor floristic elements such as Uapaca, Protea, and Burkea, co-occur, and
  • the syzygium adopts a multi-stemmed, mallee-like form where there is some accumulation of laterite (https://en.wikipedia.org/wiki/Laterite), a substrate type widespread in Australia.

In the area of Lilongwe (https://en.wikipedia.org/wiki/Lilongwe), the catena features miombo vegetation. A ‘lateritic’ layer, locally called ‘lubwe’, is exposed in places by erosion. “The lubwe always defines the lower limit of heavy leaching of the soil and is a zone of seepage...The lubwe band is characterised by the small tree Syzygium mumbwaense...This band may occur below the Uapaca zone where a drift of quartz overlies the basic complex.”

The typical catena hereabouts, from uppermost in the landforms to lowermost, is as follows:

  • on quartz sand on the hilltops, Uapaca kirkiana - Brachystegia floribunda
  • next, one step lower, Brachystegia longifolia – Faurea speciosa, a zone in which Protea abyssinica occurs as scattered plants
  • next, Brachystegia boehmii – Isoberlinia globiflora on reddish sandy soils, where Burkea africana may also occur
  • next, a zone characterised by the dwarf form Syzygium guineense ssp. huillense
  • next, Terminalia on sand, and
  • at the bottom, treeless grassland on clay in the 'dambo' (https://en.wikipedia.org/wiki/Dambo).

According to the same source, some areas of riparian forest in Malawi are co-dominated, on granitic soils, by S. cordata, S. guineense and Bridelia. In ‘swamps’ throughout the ‘low montane’ areas of Malawi, syzygiums occur to some extent.

An unidentified syzygium occurs with the palm Raphia, adjacent to streams in swampy land at altitudes of 1067 m in southern Malawi. This apparently survives despite long grass and frequent wildfires in this vegetation type.

Moving across the border to Zambia:

According to White (1962), syzygiums occur as follows.

Syzygium cordatum can grow to as high as 22 m and even occasionally has buttresses at the base. It is widespread in Zambia and dominant or co-dominant in swamp forest and fringing forest. This suggests that the vegetation dominated by S. cordatum in Amatongaland, South Africa, described above, represents a southerly attenuation of a typical vegetation type in the miombo biome.

Syzygium guineense is widespread and polymorphic in Zambia, as follows.

Hybrids between S. cordatum and S. guineense are common in Zambia.

Apart from the syzygiums already mentioned, Zambia also has S. owariense (https://www.inaturalist.org/observations/106142654), an evergreen tree up to 22m high (sometimes slightly fluted at the base), similar to S. guineense ssp. macrocarpum. Syzygium owariense occurs in the northern province and parts of central province of Zambia, and is dominant or co-dominant in swamp forest and fringing forest.

OVERALL DISCUSSION

The relationship of syzygiums in southern Africa to wildfire and herbivory seems inconsistent and needs further elucidation. However, what is clear is the polymorphism/raciality/plasticity of growth form in both of the widespread species.

In S. cordatum this is expressed mainly as a remarkable variation from stunted to arborescent. In S. guineense it is expressed mainly as a proliferation of subspecies.

Either way, what seems to emerge is that just a few species achieve the equivalent of many species, in terms of filling various ecological niches. Doe syzygiums in Australia also vary so greatly intraspecifically?

Ingresado el 26 de mayo de 2022 por milewski milewski | 2 comentarios | Deja un comentario

24 de mayo de 2022

Patterns of body size in hares

@sanjoaquinserpents @jorgejuanrueda @chewitt1 @tandala @tfrench @sammyboy2059 @capracornelius @saber_animal @ldacosta @aguilita @maxallen @marcelo_aranda @mr_fab @pelagicgraf @grinnin @jacob12_ @oviscanadensis_connerties @calebcam @galewski @dinofelis

The genus Lepus (https://en.wikipedia.org/wiki/Hare) contains about 32 species. These vary in average body mass by nearly five-fold, from about 1 kg in the smallest species to about 5 kg in the largest species.

Furthermore, this variation in body size does not generally conform to Bergmann's rule (https://en.wikipedia.org/wiki/Bergmann%27s_rule and https://www.tau.ac.il/lifesci/zoology/members/yom-tov/articles/Geographic_variation.pdf).

In this Post, I

  • list all the species of Lepus in decreasing order of body mass,
  • point out the biggest anomalies relative to Bergmann's rule,
  • seek general correlations between adaptive colouration and body size, and
  • suggest that stotting is restricted to large-bodied species plus a medium-size species characterised by pair-bonds.

The following list of the species of Lepus, in descending order of average adult body mass, is based mainly on Chapman and Flux (1990, https://portals.iucn.org/library/node/6047).

othus 4.8 kg
arcticus 4.5 kg
europaeus 3.8 kg
alleni 3.6 kg
saxatilis 3.5 kg
tibetanus (https://en.wikipedia.org/wiki/Desert_hare)/tolai (https://en.wikipedia.org/wiki/Tolai_hare) 3.5 kg
townsendii 3.25 kg
timidus 3 kg
flavigularis ?3 kg
castroviejoi 2.9 kg (https://animaldiversity.org/accounts/Lepus_castroviejoi/)
starckii 2.75 kg
callotis 2.7 kg
granatensis ?2.5 kg (https://animaldiversity.org/accounts/Lepus_granatensis/)
insularis 2.5 kg
oiostolus 2.5 kg
nigricollis 2.5 kg
brachyurus 2.5 kg
californicus 2.5 kg
capensis most subspecies ?2 kg
peguensis 2.25 kg
victoriae 2 kg
habessinicus 2 kg
comus 2 kg
fagani ?2 kg
melainus 1.84 kg
mandshuricus 1.8 kg
coreanus ?1.8 kg
sinensis 1.6 kg
hainanus 1.5 kg
yarkandensis 1.4 kg
americanus 1.3 kg
capensis subspecies omanensis and cheesmani 1 kg

The main support for Bergmann's rule lies in the fact that the largest-bodied species, namely Lepus othus, is restricted to Alaska (https://upload.wikimedia.org/wikipedia/commons/4/49/Lepus_othus_range_in_ak.png). However, this is undermined by the fact that also occurring in Alaska is the smallest-bodied species, namely Lepus americanus (https://en.wikipedia.org/wiki/Snowshoe_hare#/media/File:Lepus_americanus_map.svg).

The following photos, all taken in Alaska, show that the above two species look similar without any scale to show the nearly five-fold difference in body mass:

Furthermore, a single species, namely L. capensis, varies greatly among its subspecies within a limited range of latitudes in the Middle East (https://www.inaturalist.org/journal/milewski/42001-the-mystery-of-the-arabian-miniatures#). This is nicely illustrated by Figure 302, on page 213 of Harrison and Bates (1991).

The very smallest-bodied form of Lepus, namely L. capensis jefferyi, occurs on a coastal island in Arabia, namely Masirah Island (https://en.wikipedia.org/wiki/Masirah_Island). However, this does not detract from the fact that the subspecies of the nearby mainland in the mountains of Oman, namely L. capensis omanensis, is nearly as small-bodied. Furthermore, the subspecies of the vast sandy deserts (http://saudi-archaeology.com/background/geography-arabian-peninsula/) of the Rub al Khali (https://en.wikipedia.org/wiki/Rub%27_al_Khali), Dahana (https://www.britannica.com/place/Al-Dahna), and Nafud (https://www.britannica.com/place/al-Nafud), namely L. c. cheesemani, is also surprisingly diminutive despite occurring at medium latitudes straddling the Tropic of Cancer.

Defying any simple pattern, the smallest-bodied species and subspecies of Lepus fall into disparate ecological categories, namely

  • species adapted to forests (americanus in the subarctic and hainanus in the tropics), vs
  • species adapted to deserts (yarkandensis in northwestern China and certain subspecies of capensis in Arabia).

The general relationship between body size and adaptive colouration is as follows:

The relationship between body size and ostensible stotting in Lepus, although poorly-documented (see https://www.inaturalist.org/journal/milewski/66356-do-hares-ever-stot#), is as follows:

  • in large-bodied species (more than 3.5 kg), stotting tends to be bipedal,
  • quadrupedal stotting seems to occur only in several species (e.g. europaeus, townsendii, callotis) of body mass 2.7 kg or more, the smallest-bodied species of which (callotis) being unusual in its pair-bonded social structure, and
  • stotting of any kind has yet to be seen in any species of body mass less than 2.7 kg.
Ingresado el 24 de mayo de 2022 por milewski milewski | 6 comentarios | Deja un comentario

23 de mayo de 2022

Do hares ever stot?

I thank @lefebvremax and @beartracker for helpful discussion of this topic.

Various species of ruminants stot (https://whyevolutionistrue.com/2013/01/03/antelope-pronking/ and https://en.wikipedia.org/wiki/Stotting).

This behaviour occurs also in a large-bodied, hare-like rodent, namely Dolichotis (https://www.alamy.com/stock-photo-patagonian-mara-cavy-dolichotis-patagonum-stotting-valdes-peninsula-86749556.html and https://www.youtube.com/watch?v=bHU2RAa_-Vo and https://www.youtube.com/watch?v=e0zSyhkyycA and https://www.alamy.com/patagonian-mara-cavy-dolichotis-patagonum-stotting-valdes-peninsula-chubut-patagonia-argentina-image263028463.html and https://en.wikipedia.org/wiki/Mara_(mammal)).

The nature of stotting is basically as follows. The animal:

  • moves exuberantly, expending energy in a conspicuous and inefficient way, and
  • handicaps itself in its locomotion, as if to show off its individual fitness.

Stotting is clearly a form of self-advertisement. However, questions remain of:

  • whether the demonstration is directed towards members of the same species on one hand, or potential predators on the other, and
  • what message is being sent.

As far as I know, no naturalist has previously claimed that any lagomorph stots, at least in the quadrupedal way. The words 'hare' and 'stot' do not seem to appear in the same sentence, anywhere in the biological literature.

What have been frequently mentioned are 'observation leaps' (https://academic.oup.com/mspecies/article/doi/10.2307/3504151/2600727?login=false and https://www.researchgate.net/publication/348464180_Lagomorpha_Locomotion), in which hares in the act of fleeing intersperse their normal gallop with occasional, particularly high bounds.

Nearly all authors seem to have assumed that 'observation leaps' function not as a form of self-advertisement, but rather as a way of maintaining a clear view of the potential predator.

Therefore, in view of the above:
Establishing that Lepus stots in evolutionary convergence with ruminants and Dolichotis would be something new to science.

At present, the evidence for stotting in hares falls into three categories (besides 'observation leaping', part of the function of which remains questionable), as follows:

  • sundry photos and videos suggesting aberrations from the normal gaits of running, often in uncertain circumstances,
  • clear evidence, in a few large-bodied, ecologically extreme species, of bipedal gaits unknown in other mammals but plausibly interpreted as a form of stotting, and
  • fairly unambivalent self-advertisement in one species, which probably constitutes stotting but has not been labelled as such.

HINTS OF STOTTING IN SUNDRY SPECIES

The following photos and videos suggest subtle forms of stotting. The contexts are unclear, and in some cases may be courtship and rivalry rather than reactions to the approach of potential predators. It is also possible that hares differ from ruminants and Dolichotis in that the bouncing gait occurs not as the animal initially runs but instead as it slows down from a bout of running.

Lepus californicus: https://inaturalist.nz/observations/101996083 and https://inaturalist.nz/observations/64044230

Lepus townsendii: https://www.inaturalist.org/observations/35863227 and https://www.researchgate.net/figure/Startled-white-tailed-jackrabbit-Lepus-townsendii-in-full-flight-in-native-grass-cover-at_fig2_339086542

Lepus timidus: https://www.shutterstock.com/nb/image-photo/mountain-hare-lepus-timidus-known-blue-396645550

Lepus europaeus:
Two gaits suggestive of stotting can be seen from about 4 minutes 30 seconds in https://www.youtube.com/watch?v=ylqBH7iOXl4 and from about 1 min 45 sec in https://www.youtube.com/watch?v=q3JM0hhNOOU.
The following show possible stotting: https://www.inaturalist.org/observations/106614136 and https://upload.wikimedia.org/wikipedia/commons/1/13/Feldhase%2C_Lepus_europaeus_2a.JPG and https://www.agefotostock.com/age/en/details-photo/european-hare-lepus-europaeus-adult-male-running-stotting-back-to-female-in-grass-field-suffolk-england-march/FHR-10512-00774-842 and https://www.alamy.com/european-hare-lepus-europaeus-adult-male-running-stotting-back-to-image61827919.html and https://www.inaturalist.org/observations/73530651 and https://www.inaturalist.org/observations/73202777 and https://www.alamy.com/european-hare-lepus-europeaus-adult-male-running-with-a-bouching-gait-known-as-stotting-over-grassland-suffolk-england-february-image462643335.html.

Lepus does not normally erect its tail in flight. I suspect that stotting in e.g. Lepus europaeus sometimes features both a bouncing action and the swinging of the tail higher than usual (as seen in the first photos in each of https://www.inaturalist.org/observations/106614136 and https://www.inaturalist.org/observations/73202777). This exposes not just the white underside of the tail (which is only partly exposed https://www.istockphoto.com/photo/running-hare-gm467394605-33962244 in normal fleeing gaits in Lepus) but also a white patch of pelage on the buttocks, which is hardly noticeable in the normal action of fleeing.

BIPEDAL LOCOMOTION IN LARGE-BODIED SPECIES, possibly qualifying as stotting

See:

Only a few species of hares use bipedal gaits when fleeing from potential predators (https://www.youtube.com/watch?v=xJoB5gk8riY). It seems reasonable to interpret this as a form of stotting. Lepus arcticus and L. alleni are both unusual for hares by virtue of their large body size and their gregariousness.

In L. arcticus, both hind legs move in synchrony in the bipedal gait. However, the action is different from that in wallabies because the strides are short and rapid, and the body is held upright.

In L. arcticus, there is an additional gait in which only three legs touch the ground (https://animaldiversity.org/accounts/Lepus_arcticus/), in what amounts to a self-imposed, running limp.

APPARENT QUADRUPEDAL STOTTING IN LEPUS CALLOTIS

See Lepus callotis in https://www.inaturalist.org/posts/64011-interspecific-variation-in-flags-as-features-of-adaptive-colouration-in-hares-part-2-other-species-of-semi-arid-north-america#.

This species seems to qualify for stotting in a quadrupedal gait resembling that in ruminants..

Best and Henry (1993) state: "When flushed, L. callotis alternately flashes its white sides while running away from the intruder...Another escape behavior is that of leaping straight upward while extending the hind legs and flashing the white sides. This behavior is seen when the white-sided jackrabbit is startled or alarmed by a predator."

Seemingly relevant is the fact that L. callotis is unusual in its social structure. This species is the only hare known to occur in pairs, with an obvious pair-bond.

DISCUSSION

Much remains to be documented and interpreted with respect to possible stotting in hares.

For example, a detailed review of Lepus timidus (https://www.jstor.org/stable/3504302 and https://www.researchgate.net/publication/275737416_Lepus_timidus) makes no mention of any gaits, despite the wide distribution of this species and its close relationship to L. arcticus.

Not only 'observation leaping' but also bipedal standing at the approach of potential predators (https://www.tandfonline.com/doi/pdf/10.1080/03014220709510074 and https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1439-0310.1993.tb00544.x), when conducted in the open (https://www.gettyimages.com.au/detail/photo/jump-royalty-free-image/89348401?adppopup=true), may make more sense as demonstrations of individual fitness than as ways of keeping a potential pursuer in sight.

Regardless of the poor coverage in the past, what is already clear is the diversity of gaits (plus postures such as demonstrative, bipedal standing) listed above as candidates for stotting.

No species of Lepus stots as frequently/predictably as do certain gazelles, deer, and Dolichotis. However, where hares seem to excel is in the variety of gaits that are candidates for stotting within a single genus. I know of no genus of hoofed mammal or rodent in which such a diversity of potentially self-advertising forms of locomotion occurs.

Ingresado el 23 de mayo de 2022 por milewski milewski | 5 comentarios | Deja un comentario

17 de mayo de 2022

Caudal flags in porcupines

Various mammals possess a caudal flag. This is defined as a pattern of dark and/or pale on the tail, in some cases extending to the adjacent rump or haunches, that is inconspicuous when the figure is stationary or at rest, but conspicuous when activated by movement.

Typical examples of caudal flags occur in

'Porcupines' (https://en.wikipedia.org/wiki/Porcupine) are two families of rodents, namely Erethizontidae and Hystricidae, in which certain species have evolved extreme defences in the form of spines (https://www.inaturalist.org/journal/milewski/65187-similarities-differences-between-the-porcupines-of-different-hemispheres-erethizon-vs-hystrix-part-2#).

In this Post I ask 'which of the 28 species of porcupines possess a caudal flag'?

The answer seems to be: three species, namely Atherurus africanus and two of the eight species of Hystrix. However, all of these are odd compared with other mammals.

The caudal flag in Atherurus, which is pale (https://ainawgsd.tumblr.com/post/181842995325/embed and https://www.agefotostock.com/age/en/details-photo/african-porcupine/FTF-R10000143/1), is odd in that

  • it functions as much audially as visually,
  • it is easily lost, during the lifetime of the individual, by means of autotomy, and
  • it may be conspicuous only in ultraviolet.

The two species of Atherurus share the same design of the tail, in which the hairs of the tassel produce a rattling sound when shaken (https://animaldiversity.org/accounts/Atherurus_africanus/). However, it is only in A. africanus that the paleness of the tassel qualifies as conspicuous, at least in terms of the spectrum visible to the human eye.

The caudal flag in Hystrix africaeaustralis and H. indica (https://www.alamy.com/stock-photo-indian-crested-porcupine-hystrix-indica-also-known-as-the-indian-porcupine-124427947.html and https://www.alamy.com/stock-photo-indian-crested-porcupine-hystrix-indica-also-known-as-the-indian-porcupine-124427951.html), which is likewise pale and produces rattling sounds, is odd in that

  • it functions as much audially as visually,
  • it becomes visible only when the pelage of the body is erected, and
  • it is less conspicuous than the dark/pale pattern of the pelage of the posterior part of the body.

Although some photos of Trichys (e.g. https://www.ecologyasia.com/verts/mammals/long-tailed-porcupine.htm) show the tail tassel to be pale, this probably does not qualify as a caudal flag.

Ingresado el 17 de mayo de 2022 por milewski milewski | 1 comentario | Deja un comentario

10 de mayo de 2022

Does the North American porcupine have eye-mask colouration?

In this Post, I define 'eye-mask' (https://en.wikipedia.org/wiki/Disruptive_eye_mask) as a dark feature of animal colouration that disguises the eyes, on a figure and head that are not dark overall.

This topic has recently started to appear in the scientific literature. See:

I note that mammals possessing eye-masks tend to fall into two categories, viz.

It makes sense that the eyes are particularly inconspicuous in animals that have overall colouration designed for hiding from prey, or from larger-bodied predators. However, any functional relationship between eye-masks and warning colouration remains to be explained.

As can be seen from the examples above, eye-masks in mammals occur mainly in predatory species. They are rare in plant-eating species.

However, a possible example is Erethizon dorsatum.

Is this plant-eater one of the few rodents to possess an eye-mask? And, if so, is this related to warning colouration in this 'porcupine'?

As far as I know, these possibilities have not previously been mooted in the literature.

Warning colouration in E. dorsatum is weaker and less consistent (see https://www.inaturalist.org/journal/milewski/65187-similarities-differences-between-the-porcupines-of-different-hemispheres-erethizon-vs-hystrix-part-2#) than those in either African-Eurasian 'porcupines' (Hystrix) or the various genera of skunks (https://en.wikipedia.org/wiki/Skunk). The subtle dark/pale contrasts depend on posture and muscular movements of the skin in E. dorsatum. They are absent in some individuals, partly owing to seasonal and regional variation.

EVIDENCE OF EYE-MASK IN ERETHIZON DORSATUM

The following individuals of E. dorsatum seem to possess an eye-mask:

https://www.inaturalist.org/observations/8175871
https://www.inaturalist.org/observations/11274273
https://www.inaturalist.org/observations/10788818
https://www.inaturalist.org/observations/28411661
https://www.inaturalist.org/observations/37898442
https://www.inaturalist.org/observations/44542308
https://www.inaturalist.org/observations/33855151
https://www.inaturalist.org/observations/45805001
https://www.inaturalist.org/observations/80415227
https://www.inaturalist.org/observations/79231635
https://www.inaturalist.org/observations/78933797
https://www.inaturalist.org/observations/78111758
https://www.inaturalist.org/observations/77306649
https://www.inaturalist.org/observations/76953405
https://www.inaturalist.org/observations/69636688
https://www.inaturalist.org/observations/64210546
https://www.inaturalist.org/observations/27843255
https://www.inaturalist.org/observations/49303934
https://www.inaturalist.org/observations/47206486
https://www.agefotostock.com/age/en/details-photo/adult-male-north-american-porcupine-erethizon-dorsatum-minnesota-usa/YY4-1640900

However, the pattern is not clear-cut because, in some individuals in some seasons/regions,

Juveniles tend to be dark overall, lacking mask-colouration (https://www.istockphoto.com/photo/porcupines-gm180723145-24209220 and https://www.istockphoto.com/photo/baby-porcupine-gm157719814-22029118 and https://www.istockphoto.com/photo/baby-porcupine-gm504918032-83421755 and https://www.masterfile.com/image/en/841-03506138/a-captive-baby-porcupine-erethizon-dorsatum-animals-of and https://www.istockphoto.com/photo/baby-porcupine-gm174802022-22029114).

Some individuals are pale overall, for unknown reasons, e.g. https://www.researchgate.net/figure/An-isabelline-colored-North-American-Porcupine-Erethizon-dorsatum-from-Yukon-Canada_fig1_270904496 and https://www.inaturalist.org/observations/49305543 and https://www.istockphoto.com/photo/the-north-american-porcupine-also-known-as-the-canadian-porcupine-or-common-gm1272502547-374755167.

DISCUSSION

The anti-predator defences of Erethizon dorsatum are centred on its hindquarters, leaving the face relatively unprotected.

The carnivore most adept at killing E. dorsatum is Pekania pennanti (https://www.adfg.alaska.gov/index.cfm?adfg=fisher.printerfriendly#:~:text=Hunting%20Method,to%20descend%20trees%20head%20first). The relatively small body and elongated, weasel-like shape of this mustelid allow it to bypass the posterior spines and reach the front, whether the rodent is on the ground or climbing a tree. The carnivore thus manages to bite the face repeatedly until E. dorsatum is incapacitated.

Given that the face is, as it were, the Achilles' heel of E. dorsatum, and that most attacks occur by night, it may make sense that the rodent would benefit from its eyes being hidden. Furthermore, the inconsistency of the pattern may help to deny would-be predators - other than M. pennanti - a clear search-image in the first place.

A result of this obfuscation is that E. dorsatum is peculiarly non-photogenic even by day.

As any scrolling of the thousands of observations in iNaturalist soon shows (https://www.inaturalist.org/observations?taxon_id=44026), the photographed figure often looks almost faceless (e.g. https://www.alamy.com/close-up-portrait-of-a-porcupine-image439051825.html) unless the illumination is particularly clear.

Ingresado el 10 de mayo de 2022 por milewski milewski | 6 comentarios | Deja un comentario