24 de junio de 2022

To what extent do foliar-spinescent acacias coexist with foliar-spinescent grasses in central Australia?

@arthur_chapman @abedggood @mattbarrett @iancastle @jeremygilmore

Australia is the continent on which foliar spinescence is best-developed.

One of the largest-scale manifestations of this is the dominance of vast areas by 'porcupine grasses' (Triodia, https://en.wikipedia.org/wiki/Triodia_(plant)).

Hummock grassland (https://www.anbg.gov.au/photo/vegetation/hummock-grasslands.html and https://www.awe.gov.au/sites/default/files/documents/mvg20-nvis-hummock-grasslands.pdf), dominated by Triodia, occurs over much of the central Australian area studied by Latz (1995, https://books.google.com.au/books/about/Bushfires_Bushtucker.html?id=xlRmPgAACAAJ&redir_esc=y and https://books.google.com.au/books/about/Bushfires_and_Bushtucker.html?id=CH-uugEACAAJ&redir_esc=y).

In this vegetation, the dominant plant is hummock grass, but there are many shrubs scattered here and there. These include at least 18 spp. of Acacia that are particularly associated with Triodia, while being common enough to warrant consideration.

Some of these acacias are foliar-spinescent. Their phyllodes are terete, with ‘pungent’ tips (https://www.wordnik.com/words/pungent#:~:text=from%20The%20Century%20Dictionary.&text=Specifically%20%E2%80%94%20In%20botany%2C%20terminating%20gradually,sharp%20points%3B%20stinging%3B%20acrid.). They are thus convergent with Triodia in the extreme adaptation of the form of their foliage.
I asked the following questions for this central Australian study area:

  • of the 19 spp. of Acacia particularly associated with Triodia, which ones are foliar-spinescent? and
  • of all the Acacia spp., are the spp. with foliage most similar to that of Triodia the most strongly associated with Triodia?

According to my analysis, the answers are:

  • only a few spp. are foliar-spinescent, and
  • no, the species of Acacia most convergent in foliage form with Triodia does not coexist with Triodia; rather it tends to occur in mutual exclusion with Triodia.

This means that, in this central Australian study area, Acacia in hummock grassland is typically not foliar-spinescent, despite the foliar-spinescence of the dominant grasses.

However, the picture is complicated by the fact that many or most of the Acacia spp. occupy some sort of successional niche in hummock grassland, post-fire. In the case of those spp. most congruent with Triodia in the successional cycle, there are indeed a few foliar-spinescent spp. of Acacia.

Hummock grassland is unusual, for semi-desert vegetation, in burning intensely, and depending on wildfire for its regeneration.

When hummock grassland burns, ash is deposited. This then provides nutrients for a flush of ‘fireweeds’, which are usually soft-leafed plants living only a few years while the more slow-growing Triodia begins to recover.
Some spp. of Acacia qualify as ‘fireweeds’. This is true despite the hardness of their wood, which is one of the most important causes of tyre punctures on tracks through vegetation ‘normally’ dominated by Triodia.
In this study area, the ‘woody fireweed’ spp. of Acacia are

None of these spp. is foliar-spinescent.

Furthermore, none of them grows strictly in temporal association with the hummocks of this vegetation type. This is because they tend to senesce before Triodia achieves dominance of the vegetation. Their role is successional. Once they die, they remain only as buried, durable seeds, waiting for potentially decades before the next intense fire.
It may be a surprise that ‘fireweeds’ include such hard-wooded shrubs. However, there is no surprise that these spp. of Acacia are non-spinescent.
Then there is a category of spp. of Acacia which also occupy a successional, germinative role, but live longer and do not depend on the most intense fires for their success. It would be misleading to call these fireweeds, because they can live for several decades (albeit not as long as the plants of Triodia, which tend to continue their growth radially, in the form of rings with expanding bare centres),
These germinative, fire-promoted spp. of Acacia in the study area are

Again, none of these is foliar-spinescent. They can be found coexisting with Triodia (the acacias on the wane while the hummock grass is still on the rise). However, but they effectively form a non-spinescent upper stratum (up to a few metres high) over the grasses.
Finally, there are spp. of Acacia here which tend to regenerate vegetatively after fire. The above-ground stems tend to die in fires, but there is re-sprouting from the base. Some of these spp. are clonal, and sucker to reproduce vegetatively. The spp. are

(Another sp., namely A. minyura, https://en.wikipedia.org/wiki/Acacia_minyura, has a niche that is best characterised as similar to that of mulga (A. aneura, https://en.wikipedia.org/wiki/Acacia_aneura).)
Among these spp., there are two with spinescent phyllodes, namely

  • A. inaequilatera (which additionally possesses nodal spines), and
  • A. maitlandii (which I discuss in another Post).

Both spp. are shrubs about 2 m high.

This means that A. inaequilatera (https://en.wikipedia.org/wiki/Acacia_inaequilatera) is among the most intensely spinescent spp. in its genus. And yes, it does indeed coexist with Triodia, at more or less the stage of the successional cycle when hummock grass dominates the area. Acacia inaequilatera has corky bark protective against fire.

The additional defence in the case of A. maitlandii (https://en.wikipedia.org/wiki/Acacia_maitlandii) is a certain amount of resin (on the twigs rather than the phyllodes).
The following shows Acacia inaequilatera over Triodia https://apps.lucidcentral.org/wattle/text/entities/acacia_inaequilatera.htm. The following shows the sclerophyllous, ‘pungent’-tipped phyllodes of A. inaequilatera: https://en.wikipedia.org/wiki/Acacia_inaequilatera#/media/File:Acacia_inaequilatera_foliage.jpg.

This is an example of an intensely spinescent wattle growing together with spinescent hummock grass. However, such correspondence in spinescence between the hummock grasses and the tall shrubs growing with them is more the exception than the rule in central Australia.

The species of Acacia in the study area most strongly convergent in foliage form with Triodia is A. tetragonopylla (https://www.inaturalist.org/taxa/519206-Acacia-tetragonophylla). The phyllodes of this species are terete and ‘pungent’.

The habitat of A. tetragonophylla does not correspond to that of Triodia. Instead, this shrub occurs in woodlands and on hills, where Triodia is scarce or absent.

A reason for this mutual exclusiveness is that A. tetragonophylla relies on germination to regenerate, but also grows slowly. It is extremely drought-resistant but poorly-adapted to fire.

Ingresado el 24 de junio de 2022 por milewski milewski | 1 comentario | Deja un comentario

23 de junio de 2022

The most picturesque of antelopes and deer, in their most picturesque settings

@ludwig_muller @alex_wall @omarthenaturlist5 @noepacheco @brucebennett

Sometimes, nature throws together animals that happen to be photogenic, with surroundings that happen to be photogenic. This results in beautiful photos, combining scientific interest with aesthetic appeal.

Here, I focus on two such cases:

  • the bontebok in fynbos, and
  • barren-ground caribou in the tundra in autumn.

Fynbos, the vegetation of the southwestern tip of Africa, tends to feature splashes of colour despite being evergreen. A typical element is the protea Leucadendron (https://www.inaturalist.org/observations?taxon_id=186152), the foliage of which turns cheerfully yellow each winter (https://www.inaturalist.org/observations/122801288). Adjacent to fynbos, other vegetation types feature floral carpets of various herbaceous plants.

An indigenous herbivore of the Fynbos Biome is the bontebok (Damaliscus pygargus pygargus, https://www.inaturalist.org/taxa/42275-Damaliscus-pygargus). This subspecies, now sedentary, is easily located and photogenic throughout the year, in both sexes, and from birth to old age.

The conservation areas involved are all small, but they are easily accessible and have surprisingly diverse floras and faunas: https://en.wikipedia.org/wiki/Bontebok_National_Park and https://en.wikipedia.org/wiki/West_Coast_National_Park and https://en.wikipedia.org/wiki/Table_Mountain_National_Park#Cape_Point_section and https://en.wikipedia.org/wiki/De_Hoop_Nature_Reserve.

The caribou/reindeer is widespread in the boreal (https://en.wikipedia.org/wiki/Boreal_ecosystem) and subArctic zones. However, it is in Alaska (subspecies granti, https://en.wikipedia.org/wiki/Porcupine_caribou#:~:text=The%20Porcupine%20caribou%20or%20Grant%27s,is%20sometimes%20included%20in%20it. and https://en.wikipedia.org/wiki/Denali_National_Park_and_Preserve), and in the Northwest Territories of Canada (subspecies groenlandicus, https://en.wikipedia.org/wiki/Northwest_Territories), that its pied pattern of colouration can best be depicted in combination with the varied hues of its habitat.

Here, the cycle of moult and regrowth of the pelage is timed such that the full pattern happens to be expressed in tree-line vegetation, between the coniferous forest and the tundra. And, as it happens, this vegetation is in its full autumn colours at this time.

The ecosystems traversed by barren-ground caribou are incomparably more vast than those seen in the southwestern Cape of South Africa - regardless of the possibility that the bontebok itself was formerly migratory over modest distances. To photograph the caribou in its most picturesque settings calls for professionally organised, specialised tours to remote areas.




















scroll in https://www.canadiannaturephotographer.com/arcticadventure2014.html


Ingresado el 23 de junio de 2022 por milewski milewski | 2 comentarios | Deja un comentario

Caleonic colouration in the caribou, part 2

(writing in progress)

As I see it, the major differences among the main three main forms of Rangifer tarandus in North America are as follows.

I focus on the fully mature male in autumn. Differences can be seen in antler form and colouration patterns. 
Barren-ground type (typically groenlandicus and granti, https://photos.alaskaphotographics.com/img-show/I0000pqZ2U_D_aI8 and https://www.alamy.com/stock-photo-sideview-of-an-adult-bull-caribou-walking-along-a-ridgetop-near-highway-40002640.html?imageid=B658E192-A8DF-42E2-8FEC-856427CAFA0B&p=228470&pn=6&searchId=d45a0b079e0a44d6df19e063f123082f&searchtype=0 and https://www.alamy.com/stock-photo-a-bull-and-cow-caribou-in-the-alaskan-range-mountains-during-the-autumn-126175283.html?imageid=FCD3A92E-5377-4F5B-A54A-A1E9CA2572AB&p=194525&pn=1&searchId=26929b68aec462c7654cb43d9dd2f7a4&searchtype=0 and https://www.alamy.com/stock-photo-a-bull-and-cow-caribou-in-the-alaskan-range-mountains-during-the-autumn-126175284.html?imageid=4928F00C-F791-45EC-93BC-1A700551D8D6&p=194525&pn=1&searchId=26929b68aec462c7654cb43d9dd2f7a4&searchtype=0 and https://www.alamy.com/stock-photo-a-bull-caribou-follows-his-harem-in-the-alaska-tundra-during-the-autumn-102726416.html?imageid=51D937F6-E643-48FC-B5B3-89DE79BD20A6&p=194525&pn=1&searchId=26929b68aec462c7654cb43d9dd2f7a4&searchtype=0):

  • posterior parts of antler emphasised, with minimal palmation
  • colouration pied; overall, tonally balanced (approximately equal areas of dark and pale, in profile)
  • flank-banding maximal
  • pale feature near elbow

Insular type (pearyi https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/peary-caribou-barren-ground/chapter-4.html and terranovae https://saltscapes.com/roots-folks/3205-caribou-country.html and scroll Inn https://trophyhunts.com/listing/steel-mountain-lodge-newfoundland-canada-fly-in-hunting-lodge-for-moose-and-caribou/ and https://mobile.twitter.com/ducboreal/status/1369313314820521990 and https://m.facebook.com/NewfoundlandLabradorTourism/photos/a.111088443781/111092763781/?type=3 and https://www.alamy.com/stock-photo-large-bull-caribou-with-shedding-velvet-antlers-walks-through-crimson-75290365.html?imageid=3A3FE78C-D4D3-4C1F-93D3-567A2543B15E&p=228679&pn=25&searchId=9892403e79eeaa448727cb13a1e36c01&searchtype=0):

  • antler form moderate
  • colouration pallid
  • flank-banding minimal (by means of pallour)
  • pale extension on haunch

Woodland type (typically caribou sensu stricto, https://www.alamy.com/stock-image-male-woodland-caribou-rangifer-tarandus-caribou-central-british-columbia-162739550.html?imageid=705471E7-CC68-4E93-BE30-678AC46531C4&p=281926&pn=4&searchId=d557ba6763acd5a93532c35ee5eb7dff&searchtype=0 and https://www.alamy.com/stock-photo-woodland-caribou-rangifer-tarandus-caribou-bull-northern-british-columbia-125476288.html?imageid=B8781D2E-37BA-4870-8F53-467D9A3A15BD&p=360763&pn=19&searchId=ca9b65ac9c231055a4ff7c926e1bb949&searchtype=0 and https://market.newfoundlandcanvas.com/bradjames/woodland-caribou-1 and https://kidadl.com/facts/animals/woodland-caribou-facts and https://www.tbnewswatch.com/local-news/first-nations-criticize-caribou-protection-plan-692585):

  • anterior parts of antler emphasised, with maximal palmation
  • colouration dark (even the neck failing to become white in autumn)
  • flank-banding minimal (by means of darkening)
  • pale feature near elbow

If there are three major types of Rangifer tarandus in North America, then the question arises: which environmental differences have produced this differentiation?

The following occurs to me, bearing in mind that for cervids one of the most important aspects of the environment is avoidance of other ruminants of similar body-size.

In general, the pattern for large (>20 kg) cervids everywhere in the temperate to polar Northern Hemisphere, plus tropical to temperate South America, is that only one species occurs in a given area. Cervids tend to be mutually exclusive in habitat although there are situations of coexistence of a large species with a small species.

Whereas a theme among bovids is coexistence in multi-spp. communities, cervid spp. tend to compete/indirectly interfere with each other to the effect that only one sp. can succeed in any given area.

Indeed, this is part of the reason for the decline in the true woodland caribou (R. t. caribou sensu stricto) in the western part of the boreal zone of North America. With logging, the habitat of this form has supported an increase in Alces alces or forms of Odocoileus, or both. These forms, even if they do not compete with R. tarandus for food, tend to support too many predators for the populations of R. t. caribou to sustain the losses in the longer term./What occurs to me about the three major forms of R. tarandus in North America is the following:

The barren-ground sspp. (mainly groenlandicus and granti) coexist partly with Alces alces and Ovis dalli but tend to spend a crucial time of year (summer) in a remote extreme environment free of other ruminants (and with limted predation).

The forms found on islands (sspp. pearyi and terranovae) were (until the introduction of Alces alces to Newfoundland) essentially free from coexistence with other ruminants; coexistence was irrelevant to any longer-range movements they performed.

The woodland and mountain sspp. (e.g. caribou sensu stricto) were the most subject to coexistence with other ruminants, of all the three types. The ruminants concerned included Alces alces, several forms of Odocoileus, and forms of Ovis; and the coexistence potentially occurred throughout the seasonal cycle. This means, inter alia, that the natural densities of populations of the woodland and mountain forms of R. tarandus were everywhere limited, which affects population-related phenomena such as rutting behaviour the sexual displays.

The point of this conceptual framework, with particular reference to R. t. terranovae of Newfoundland, is the following. It may seem surprising, given that Newfoundland is a large island and not remote from the mainland, that the form of R. tarandus on it is so distinctive (and so similar to the remote Arctic R. t. pearyi, which lives at a far lower latitude with a far more extreme climate). However, R. t. terranovae was unusual, among all the forms of R. tarandus at its latitude, in having its whole habitat to itself w.r.t. other ungulates.

I offer the following summary of the ideas introduced here:

Migratory (barren ground) types: pied colouration; free of other ruminants in summer; relatively free of predation in summer/Island types: pallid colouration; permanently free of other ruminants; predatory pressure set by R. tarandus itself

Woodland/mountain types: dark colouration; permanently subject to coexistence with at least one other sp. of ruminant; predatory pressure potentially disproportionate year-round.

Continuing this line of thinking, we may go on to ask:

Given that the colouration of all forms of R. tarandus has conspicuous aspects and inconspicuous aspects, how are the different patterns of colouration potentially adaptive to the different predatory regimes?

I offer the following tentative answer:

Migratory types: extremely conspicuous at the season of relative freedom from predation, somewhat inconspicuous at the season of relative intensity of predation/Island type on Newfoundland: extremely conspicuous in summer, inconspicuous in winter (when its extreme pallor blends in with snow)

Woodland/mountain types: somewhat inconspicuous year-round, including winter when the background consists of not only snow but also trees and shrubs.

(writing in progress)

Ingresado el 23 de junio de 2022 por milewski milewski | 28 comentarios | Deja un comentario

22 de junio de 2022

Caleonic colouration in the caribou, part 1

(writing in progress)

A well-recognised form of conspicuous colouration in medium-size to large animals is the pied pattern (https://www.tripadvisor.com/LocationPhotoDirectLink-g469397-d469470-i381557535-Bontebok_National_Park-Swellendam_Overberg_District_Western_Cape.html and https://www.flickr.com/photos/myplanetexperience/50867088327). This consists of a dark/pale patchwork too bold to function disruptively, i.e. for camouflage.

However, another conspicuous pattern, less familiar but obvious in certain mammals, deserves a name. I provisionally call this 'caleonic colouration'.

Caleonic colouration has arisen repeatedly in lineages as diverse as

It is normal for the ventral parts of the body to be pale, as part of the inconspicuous pattern called cryptic colouration (https://en.wikipedia.org/wiki/Countershading). However, the extension of this pale switches the effect to conspicuousness. This is because the pale, encroaching upwards towards the dorsal side, tends to catch the sunlight at all seasons and most times of day.

This ‘lateralisation’ of the pale parts of the pelage occurs variously on the cheeks, neck, shoulders, flanks, and/or hindquarters. In extreme cases it reaches the dorsal surfaces of the rump, the neck, and even the back. This achieves whole-body conspicuousness for gregarious species living in the open, where it is hard to hide anyway.

In the caleonic pattern, the figure is 'highlit' by what seems to be a flame located below it.

In a sense, animals with caleonic colouration have ‘inverted’ the principle of countershading, to achieve whole-body conspicuousness instead of crypsis (https://en.wikipedia.org/wiki/Crypsis). This differs from the pied pattern, in which countershading is redundant owing to the large-scale dark/pale contrast in the pigmentation of the pelage.

In this series of Posts, I show that the widespread species Rangifer tarandus (https://www.inaturalist.org/taxa/42199-Rangifer-tarandus) has certain subspecies with pied colouration, and others with caleonic colouration. This arguably makes it the only species of mammal in which both patterns occur, depending on the location.

(Besides R. tarandus, the only species which I know to possess caleonic colouration in only certain populations is the domestic horse Equus caballus. However, this is qualified by the likelihood that the domestic horse has arisen by hybridisation among several wild congeners during the process of selective breeding.)

Please bear in mind that R tarandus undergoes seasonal moult of the pelage, in which the pigmentation wears out during the winter, and the re-growing fur initially looks fairly uniform in of spring/early summer, before the hairs acquire their full effect. Thus the fully-differentiated colouration tends to be expressed in autumn, corresponding to the rutting season.

The following shows pied colouration in Rangifer tarandus: https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057000.html?imageid=CA708987-0B78-4D58-A301-7570ACD15211&p=365985&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-with-female-calf-on-migration-south-41499424.html?imageid=24FDBEC7-2515-4910-A5C6-57A0352BEF7C&p=54193&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-female-in-snow-on-migration-south-through-41499304.html?imageid=013FADBA-BE26-48E8-96CC-B83A1BEDFC74&p=54193&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057056.html?imageid=8BFBDFF1-5FE8-4504-BC54-0C1ED673978D&p=365985&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/caribou_trails/caribou_trails_2014.pdf.

The following shows caleonic colouration in Rangifer tarandus: https://www.inaturalist.org/observations/28836472 and https://www.natureinstock.com/search/preview/woodland-caribou-rangifer-tarandus-caribou-bull-in-town-newfoundland-canada/0_10121446.html and https://www.mindenpictures.com/stock-photo-woodland-caribou-rangifer-tarandus-caribou-male-newfoundland-canada-naturephotography-image00596574.html and https://m.facebook.com/NewfoundlandLabradorTourism/photos/a.111088443781/111092763781/?type=3 and https://www.inaturalist.org/observations/9039103 and https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/38196369.

Pied colouration occurs in the autumn coat of most of the subspecies of Rangifer tarandus, including R. t. groenlandicus and R. t. granti. The darkest parts are muzzle, forelegs, brisket, and lower flanks, while the palest are nose (rhinarium), neck, beard/dewlap, tail and the narrow rump-blaze. These features are arranged to provide dark/pale contrast, not crypsis or disruption of the outline of the animal.

Caleonic colouration occurs in the subspecies found on two systems of islands, far apart geographically. On the Arctic islands occurs subspecies, R. t. pearyi (https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/mammals/peary-caribou.html and https://www.inaturalist.org/guide_taxa/1119027 and https://www.alamy.com/stock-photo-bull-caribou-in-velvet-antlers-stands-in-the-colorful-autumn-tundra-75290355.html?imageid=89F3DD5C-43FB-48AC-B540-F92A8006B30D&p=228679&pn=25&searchId=9892403e79eeaa448727cb13a1e36c01&searchtype=0). On the island of Newfoundland (https://en.wikipedia.org/wiki/Newfoundland_(island)) occurs subspecies, R. t. terranovae (https://www.naturepl.com/stock-photo-woodland-caribou-nature-image00596572.html and https://www.shutterstock.com/de/image-photo/caribou-adult-female-rangifer-tarandus-avalon-1911012163).

I agree with Valerius Geist that R. tarandus on the island of Newfoundland is quite distinct from other forms of ‘woodland caribou’, and that taxonomy took a wrong turn when R. t. terranovae was lumped with R. t. caribou.

The following illustrate R. t. terranovae: https://mobile.twitter.com/NFLDdesigns/status/1339255210749865986/photo/1 and http://www.nlnature.com/Newfoundland-Canada-Nature/1520.aspx and http://birdingnewfoundland.blogspot.com/2009/12/southern-avalon-peninsula-birds-and.html and second photo in https://www.cbc.ca/news/canada/newfoundland-labrador/reindeer-deer-lake-video-1.4918560.

In the pied pattern, the lower flanks, chest, lower shoulders, and brisket are the darkest parts of the animal. This differs from the caleonic pattern in R. t. terranovae, in which all these parts are the palest parts of the animal. It is hard to see how the two patterns of colouration in R. tarandus, namely pied and caleonic, can be represented as extremes on a continuum. Instead, what seems to have happened is that in an ancestral form the whitish at the belly has spread so far up that it has replaced the entire flank-band complex in the pied pattern, while at the same time the legs have gone from basically dark to basically pale, and the neck has acquired a darkish dorsal zone in the caleonic pattern.

In Rangifer tarandus terranovae, I find at least three aspects detracting from any simple characterisation of the pattern as caleonic:

  • some individuals do retain a faint version of the flank-banding typical of most subspecies of R. tarandus,
  • the pale of the neck tends to be disjunct from the pale of the shoulders and flanks, separated by a more-or-less vertical tract of pale greyish-fawn fur, and
  • the pale of the lower haunch tends to give way to a darker tone on the upper leg in some individuals.

What this means is that the pattern of colouration in R. t. terranovae is not categorically different from that in other subspecies. However, the combination of a caleonic tendency (particularly on flank and haunch) and an overall pallour set this subspecies apart from all other subspecies besides R. t. pearyi. Whereas ‘woodland caribou’ in the western part of the boreal zone of North America are unusually dark for the species (e.g. according to Valerius Geist), R. t. terranovae is unusually pale, particularly considering that it lives at a far lower latitude than pearyi.
Please see e.g. https://www.wildandexposed.com/journal/2018/10/17/marks-adventures-in-newfoundland
I take the following to be in July or August. Last year’s guard pelage is still moulting.
The following, probably in July, shows the extreme pattern of colouration, so different from that of other R. tarandus (except for pearyi). The diagonal border between darker and paler on the haunch is diagnostic of terranovae, and does not occur in the other subspecies of R. tarandus including pearyi. This photo shows the fresh underpelage of summer; the guard pelage has yet to appear. Note that the face is the darkest part of the animal (with one patch of last year’s guard pelage still to fall out completely). Note that the whitish extends above the knee, which is consistent with caleonic colouration.

The following is of the mature male, probably in August-September, with the guard pelage emerging on the neck. The diagonal tonal contrast on haunch is diagnostic of R. t. terranovae.

The following is similar seasonally to that above, but the face not as dark, and the knee region not included in the pale tract.

I take the following to be the mature male in September, in something approaching the pattern of colouration of the autumn. There is no trace of the flank-banding typical of most subspecies of R. tarandus.

I take the following to be in August, with the new underpelage complete. In this case the pale diagonal on the haunch gives way to darker on the upper hind leg.

The following two male individuals, probably in September, show some features linking the ‘typical’ pattern above to the pattern typical of other subspecies of R. tarandus. These include the relative darkness of the legs and the faint banding on the flank. These detractions notwithstanding, this colouration remains different from those of any other forms of ‘woodland caribou’ at the same season.

I take the following to be in September, just before the rutting season. This individual has a pattern on its flank which is a faint version of that in most other subspecies of R. tarandus. However, the difference remains that the colouration is pallid instead of pied.

The right-hand photo below shows what I take to be the mature male in autumn, during the rutting season. Note the separation of the pale of the neck from the pale of the elbow region.

I take the following to be the adolescent male in autumn. The side of the body shows a faint version of the banding seen in most subspecies of R. tarandus. The face is not dark here as it is in several of the males above which I assume to be because the guard pelage has emerged on the face.

If the following is in autumn, it illustrates the point that in terranovae there is no pied pattern of colouration.

Because both sexes are in hard antler together, I take the following two photos to be in autumn, near or in the rutting season. In the first of these two photos, two of the female individuals plus the juvenile retain, albeit in pallid form, the flank-banding typical of other sspp. of R. tarandus, which detracts from the caleonic pattern.
The mature males in the following show the typical colouration of terranovae.

I take the following two photos to be in September, with the colouration approaching that of the rutting season.

I take the following to be in the rutting season. This colouration is different from the pied colouration of R. t. groenlandicus and R. to granti in the rutting season.

I have pointed out, above, that some individuals of R. t. terranovae have a faint version of the flank-banding seen in other subspecies of R. tarandus, and that this detracts from/tends to compromise the caleonic pattern. However, this may perhaps be owing to some degree of anthropogenic mixing with another subspecies.
Wilkerson (2010, https://www.mun.ca/biology/scarr/Wilkerson%202010,%20excerpt.pdf) states that the domestic reindeer (R. t. tarandus) was introduced to the island of Newfoundland early in the twentieth century, and that there was indeed contact between this subspecies (which possesses flank-banding) and the indigenous populations, viz R. t. terranovae

My hypothesis is therefore that the original appearance of the Newfoundland form was truly caleonic to the exclusion of the flank-banding.

(writing in progress)

Ingresado el 22 de junio de 2022 por milewski milewski | 5 comentarios | Deja un comentario

The odd bird that is the musk duck

(writing in progress)

There is an unremarked similarity between the musk duck (Biziura lobata, https://www.inaturalist.org/taxa/7178-Biziura-lobata) and the platypus (Ornithorhynchus anatinus, https://www.inaturalist.org/taxa/43236-Ornithorhynchus-anatinus).
The following video shows the musk duck fairly well: https://www.youtube.com/watch?v=xWwoMvfTcGk .
Both the platypus and the musk duck are restricted to Australia (mainly the cooler parts). They are as peculiar as anyone might wish, as ‘Australian specialities’. The musk duck is the largest freshwater duck on Earth, and is peculiar relative to other waterfowl in various other ways.

Both platypus and musk duck are so specialised for swimming that they can hardly locomote on land (although of course the platypus burrows extensively at the water’s edge). In both the platypus and the musk duck, the male produces a musky odour at breeding time.
The body sizes, diets and foraging methods of platypus and musk duck are similar, and the two species look so alike in the water that they are sometimes confused by naturalists. The beak of the musk duck, perhaps more than other waterfowl, is similar to the beak of the platypus. The swimming methods are similar although it is the front feet with which the platypus paddles. Of course, both forms lay eggs.
It strikes me as surprising that evolution in Australia has produced such similar animals, sharing the same trophic guild and in some areas coexisting, but drawn from the mammals in one case and from the birds in the other case. How are these forms ecologically separated, given that they seem to compete for similar foods?

The musk duck is able to fly to water bodies too temporary to allow residence by the platypus, but I have yet to see this stated in the literature in the context of ecological separation within a guild. Are there permanent water bodies in eastern Australia that are inhabited continually by both the platypus and the musk duck?
With respect to brain size, what is interesting is that, just as the platypus is rather brainy for such a primitive mammal, so the musk duck is brainy for a waterfowl (Iwaniuk and Nelson 2001). This braininess is particularly intriguing in view of the fact that the musk duck is among the few waterfowl known to be able to mimic vocally.
The platypus has mean brain mass 10.1 g at body mass 1.4 kg, whereas the musk duck (n =9 individuals of unstated sex) has mean brain mass of 9 g at body mass 2 kg. Since the male musk duck is considerably larger than the female, I suspect that female brain mass in the musk duck is < 9 g. What this means is that there remains a difference in brain size in keeping with the general rule that large birds tend to have lighter brains than those of like-size mammals.

Although the musk duck is brainy for an anatid, and the platypus is ‘reptilian’ for a mammal, there remains a gap between them in brain size.
Most waterfowl of about the body mass of the musk duck have brain mass about 6.9 g. The Australian shelduck (Tadorna tadornoides, https://www.inaturalist.org/taxa/7070-Tadorna-tadornoides) happens to have the same body mass as the platypus (1.4 kg) but a brain of only 5.7 g. And the merganser (Mergus merganser, https://www.inaturalist.org/taxa/7004-Mergus-merganser), which lives far from Australia, also happens to have a body mass of 1.4 kg with brain mass only 5 g.

Note that the merganser has a brain only half the mass of that of the platypus, at similar body mass.

So the platypus has a far larger brain than those of the like-size shelduck and merganser, and a slightly larger brain than that of the coexisting musk duck, with other waterfowl of comparable body masses (e.g. Alopochen, Anser, Aythya, Melanitta, Somateria) in between.  
Musk duck (Biziura lobata):

Platypus (Ornithorhynchus anatinus):

Musk duck (Biziura lobata):

Here are more facts about braininess in the musk duck (Biziura lobata). My source is Iwaniuk and Nelson (2001).
Firstly, there is a nice contrast between the musk duck and another ‘Australian speciality’, namely the Cape Barren goose (Cereopsis novaehollandiae, https://www.inaturalist.org/taxa/7150-Cereopsis-novaehollandiae). Whereas the musk duck is perhaps the most encephalised anatid in Australasia, the Cape Barren goose is the least encephalised of all the anatids sampled by these authors worldwide.

What this means is that simply being an ‘Australasian speciality’ predicts little w.r.t. braininess.

Nobody should be surprised to find that a grazing goose, ecologically comparable with the emu (Dromaiu novaehollandiae, https://www.inaturalist.org/taxa/20504-Dromaius-novaehollandiae) and bearing precocial offspring, and furthermore associated with islands off an island continent, is small-brained – even relative to the standards of anatids, which are among the smaller-brained of birds.

However, it is surprising that a species as peculiarly Australian as the musk duck is large-brained.
Secondly, it just so happens that the absolute brain masses are similar in musk duck and Cape Barren goose: about 9 g. (Note that Iwaniuk and Nelson 2001 give brain sizes in ml, and I have used a factor of 1.03 to convert these volumetric data to masses.) What is nice, in illustration of the extreme difference between the musk duck and the Cape Barren goose w.r.t. encephalisation, is that they share a single brain mass (about 9 g) despite the fact that their body masses are more than two-fold different (2 kg for musk duck compared to 4.5 kg for Cape Barren goose).
Thirdly, another ‘Australian speciality’, the magpie goose (Anseranas semipalmata, https://www.inaturalist.org/taxa/6905-Anseranas-semipalmata) just so happens to have similar brain mass again: about 9 g. Because its body mass is 2.4 kg, it is close to average in brain/body mass for an anatid – despite any peculiarities it may have in terms of diet etc.
The only other anatid in the data-set with brain mass very approximately 9 g, namely the white-fronted goose (Anser albifrons, https://www.inaturalist.org/taxa/7019-Anser-albifrons), is also worth mentioning because it is below-par in braininess but not as extremely so as is the Cape Barren goose. Both the white-fronted goose and the Cape Barren goose are ‘grazers’, but the former bird, grazing the tundra in summer and migrating far south within the Northern Hemisphere in winter, does not live in the kind of isolation, virtually protected from predators, that the insular Cape Barren goose enjoys.
Fourthly, the discussion by Iwaniuk and Nelson (2001) of the braininess of the musk duck is worth reading. The musk duck is odd among anatids in minimising the number of eggs per clutch and in having parental feeding of hatchlings and juveniles.

Almost all species of anatids have precocial offspring which, although guarded by parents, forage for themselves from the start. The peculiarity of parental care in the musk duck, although unique in detail, seems to echo a theme in the Australian fauna: odd reproductive habits.

It could even be framed as some sort of convergence between musk duck and platypus that both provide for their offspring, the former by feeding its chicks small invertebrates and the latter by oozing milk. The niche of invertebrate-eating diver in freshwater might have been expected to be filled by ‘normal’ diving ducks in Australia, but instead the forms sharing this niche on the island continent are both aberrant in showing more parental provisioning and more encephalisation than expected in waterfowl.

It seems odd that one of these niche-occupiers is an aberrantly non-buoyant duck, and the other is a duck-billed, egg-laying mammal (monotreme). However, it leads to various questions once one overcomes the traditional reluctance to compare across the bird-mammal divide.
The following zoom-in shows a horizontal line-up of spp. at the value of about 9 g for brain mass in four spp. of anatids. The left-most is musk duck, which is encephalised. The right-most is Cape Barren goose, which is either decephalised or primitively unencephalised owing to island life, relatively free of predation. The two intermediate points are magpie goose on the left (only a tad brainier than expected for the average anatid) and white-fronted goose (which is like a Northern Hemisphere version of the Cape Barren goose). The white-fronted goose is a tad less brainy than expected for the average anatid.
Cape Barren goose (Cereopsis novaehollandiae):
(writing in progress)

Ingresado el 22 de junio de 2022 por milewski milewski | 1 comentario | Deja un comentario

21 de junio de 2022

Comparison of the cycads Zamia and Macrozamia

If one lives in Australia or South Africa, as I have done for most of my life, one tends to get the impression that cycads have tough, plastic-like leaves. If one pays attention to details, one also gets the impression that these tough leaves have spinescent pinnae. Thus one forms a certain impression of ‘the typical cycad’, and this impression is of a leaf-spinescent plant.
In this Post, I focus on a tropical American genus of cycads, namely Zamia, which contains many (53) species. The point is to show that there are plenty of cycads in the world that have leaves of ‘normal’ texture, lacking spines on the pinnae. These spp. generally live in rainforests, free from fire.

And in this genus, Zamia, the ecological versatility of cycads is so great that at least one species qualifies as an epiphyte, and another as a denizen of mangroves.
My source is D L Jones (2002). This author provides the species-descriptions but makes no attempt to synthesise the intergeneric comparisons in the way I do here.
Please bear in mind that in terms of habitat the two genera have different emphases. Zamia typically occurs in tropical rainforest, although some species occur in savannas. By contrast, Macrozamia typically occurs in various types of relatively open, fire-prone vegetation at higher latitudes, and never penetrates tropical rainforest, let alone equatorial rainforest.

However, it seems fair to compare Zamia living in Florida with Macrozamia living in southeastern Queensland.
Although most spp. of Zamia have pointed pinnae with small teeth (which Jones describes in some cases as ‘spiny’), neither the tip of the pinna (which is never described as ‘pungent’ in this genus) nor the teeth on its margin seem to be able to hurt the human hand. What this means is that in the great majority of spp. the pinna is not, in fact, spinescent (although I cannot rule out some sharpness similar to that of ‘saw-edged’-sedges).
Although Zamia lacks leaf-spinescence on the leaf-blades themselves, many spp. of Zamia do possess a different kind of leaf-spinescence:

  • prickles on the rhachis in some spp., and
  • prickles on the petiole in most spp.

In e.g. Zamia chigua, the prickles on the petiole are described as including ‘branched’ prickles, whatever that means.
Overall, the ‘typical’ species in genus Zamia has a spinescent petiole but non-spinescent pinnae.
In this way, Zamia can be seen as the ‘opposite’ to the genus Macrozamia of Australia. This is because Zamia

  • tends to have spinescent petioles whereas Macrozamia never does,
  • has the petiolar prickles in some cases extending on to the rhachis, whereas no sp. of Macrozamia has spines on the rhachis,
  • lacks the spiny tip to the pinna which is so common in Macrozamia, and
  • often has ‘teeth’ on the margins of its pinnae, which Macrozamia lacks, although neither genus has spinescent margins to the pinnae.

Although certain spp. of Zamia are sclerophyllous (leaves described by Jones as ‘thick and leathery, stiff, rigid’ in the case of e.g. the horticulturally popular Z. furfuracea), other spp. of Zamia have leaves so thin that the leaves of Z. hymenophyllidia are described as ‘membranous’! What is particularly significant about this is that even in this membranous-leafed sp. the petioles retain ‘very small prickles’.
What this indicates is that petiolar spinescence is adaptively ‘decoupled’ from pinnal spinescence, not so? Petiolar spinescence lacks a relationship with sclerophylly, and this is as true in cycads as it is in plants generally.
Zamia integrifolia is worth mentioning specifically, because it shows that even a species adapted to open vegetation in relatively dry climates remains non-spinescent. Zamia integrifolia is widely distributed from southeastern Georgia in the USA to certain Caribbean islands and the Bahamas. It was once abundant in Florida, where its stems were exploited for edible starch by the Seminole native Americans, just as the same species was exploited in the Caribbean by the Arawak native Americans.

Despite being so subject to damage, despite growing in fire-prone vegetation, and despite having ‘stiff, leathery’ pinnae, Z. integrifolia is non-spinescent. Its petioles lack prickles. Its rhachis accordingly lacks prickles. The pinna, far from being ‘pungent’, has that rare thing for a cycad, a blunt apex! And even the marginal ‘teeth’, so common in Zamia, are in this species small and blunt, described as mere bumps, i.e. far from spinescent.
At a casual glance, Zamia integrifolia, which is regarded as hardy and adaptable in horticulture, looks much like the typical form of Macrozamia (Australia) or Encephalartos (Africa). However, on closer inspection it proves to be lacking in any spines. And in this case this cannot be explained by an association with rainforest.  
The most epiphytic species of Zamia, Z. pseudoparastica, has a few prickles on its petiole, a non-spinescent (non-prickly) rhachis, and non-spinescent pinnae. Intriguingly, the diaspores of this specialised cycad are aberrant in having the sarcotesta sticky-mucilaginous and with a distinctive sour smell, presumably in aid of dispersal by fruit-eating bats and birds. Here we see convergence with mistletoes in the mutualism with vertebrates in aid of dispersal and sowing in suitable sites, i.e. on branches rather than on the ground.
At least one species, Zamia roezlii, occurs in mangroves, where it may be flooded by high tides. And this species, occurring in e.g. Ecuador, is also non-spinescent.
I assume that Zamia, which is known to be toxic, relies on toxins to the exclusion of leaf-spinescence in its pinnae. However, I have yet to explain why Zamia would opt for spinescence on its petioles.
I can summarise these differences as follows:
In both the Australian genus Macrozamia and the American genus Zamia, some spp. lack any spinescence in their leaves. However, those spp. which are leaf-spinescent differ in a basic way between the two genera. Macrozamia defends its leaves from herbivores by ‘marginal’ spinescence, whereas Zamia defends its leaves from herbivores by ‘basal’ spinescence.

In Macrozamia, the spinescence is distal; in Zamia, proximal. I.e. in Macrozamia the spinescence is at the tips of the pinnae (and not on the petioles), a pattern consistent with sclerophylly.

By contrast, in Zamia the spinescence is on the petioles, not at the tips of the pinnae. This is instead consistent with non-sclerophylly, i.e. with a flimsy (papery rather than leathery) texture to the leaves.
I find it surprising that these major groups of cycads take such different approaches to anti-herbivore defence. It almost seems that the pressures of herbivory in equatorial rainforests tend to be qualitatively different from those in the various kinds of open vegetation in temperate-zone Australia.
And the notion that cycads are anachronistic ‘dinosaur plants’ is obviously false, in view of the versatility of cycads even in rainforests.


Zamia 'maritima', showing the prickles on the petiole.

Zamia integrifolia, which looks superficially like Macrozamia but is in fact non-spinescent, lacking spines even on the petiole.
https://garden.org/plants/photo/555455/ and https://tropical.theferns.info/viewtropical.php?id=Zamia+integrifolia and https://florida.plantatlas.usf.edu/Photo.aspx?id=19723 and https://en.wikipedia.org/wiki/Zamia_integrifolia
Zamia furfuracea, showing the prickles on the petiole. This species has sclerophyllous pinnae but the pinnae are not spinescent. Instead, it is the petiole which is spinescent.
https://austinbotany.wordpress.com/2015/03/14/zamia-furfuracea-cardboard-palm/ and https://www.baobabs.com/Fiche2.php?Lang=en&Ref=582 and https://www.florida-palm-trees.com/cardboard-palm-tree/ and https://en.wikipedia.org/wiki/Zamia_furfuracea

Ingresado el 21 de junio de 2022 por milewski milewski | 0 comentarios | Deja un comentario

A user-friendly guide to braininess in mammals

Fig. 1 in http://www.pnas.org/content/107/37/16216.full compares brain sizes, relative to body sizes, in various lineages of mammals. This constitutes a powerful summary that will be of interest to many readers.

However, most naturalists may find some of the categories so complicated as to be baffling. So, here is a user-friendly guide to the interpretation of this chart.
Braininess can be defined as brain size relative to body size, using a mathematical correction for scaling factors. Braininess can be quantified as Encephalisation Quotient (EQ, https://en.wikipedia.org/wiki/Encephalization_quotient), which by definition has a value of 1 for the average mammal.
Please note, immediately, this study omits the monotremes (https://en.wikipedia.org/wiki/Monotreme).

Marsupials (https://en.wikipedia.org/wiki/Marsupial) are divided into several clades. Indeed, in this classification, marsupials are not a coherent category as such. For example, American opossums (https://en.wikipedia.org/wiki/Opossum) are unrelated to Australian possums (https://en.wikipedia.org/wiki/Possum), being convergent rather than stemming from a common ancestor.

Equally surprising, in the opposite way, is that primates (https://en.wikipedia.org/wiki/Primate) share the same clade as rodents (https://en.wikipedia.org/wiki/Rodent). This means that we humans are more closely related to rats than possums are to opossums.

And then, as if to discourage any lay person trying to fathom this chart:
One clade, namely Laurasiatheria (https://en.wikipedia.org/wiki/Laurasiatheria), is so extremely diverse that it ranges from bats to whales and from skunks to zebras.
Not allowing ourselves to be deterred by these bewildering cladistic associations, let us move from left to right across the same chart (Fig. 1 in http://www.pnas.org/content/107/37/16216.full).
On far left we have Peramelemorphia (https://en.wikipedia.org/wiki/Peramelemorphia), the group of marsupials consisting of bandicoots and the bilby. These marsupials have particularly small brains. Look at the great difference in relative brain sizes between bandicoots and the human species, which is the solid dot in the column for Euarchontoglires (https://en.wikipedia.org/wiki/Euarchontoglires), and located right at the top of the chart.
The values second from left refer to the large and diverse group including kangaroos, wombats, possums, etc. As readers can see, Diprotodontia (https://en.wikipedia.org/wiki/Diprotodontia) tend to have relative brain size less than the average for mammals, but not as extremely so as in the bandicoots.
The next two columns, third and fourth from left, refer to the dasyurid marsupials (Dasyuromorphia, https://en.wikipedia.org/wiki/Dasyuromorphia) and the American opossums (Didelphimorphia, mentioned above). Both groups have relative brain sizes not much different from the mammalian average. This, by the way, is one of the reasons why I find it significant that both the marsupial lion (Thylacoleo) and the thylacine (Thylacinus) are inferior in EQ to Carnivora (see my other Post).
So far, what this means is that a quoll (Dasyurus, https://en.wikipedia.org/wiki/Quoll) is likely to be brainier than a dorcopsis (think rat-kangaroo, https://en.wikipedia.org/wiki/Dorcopsis) of similar body size, which in turn is likely to be brainier than a bandicoot of similar body size. And the Virginia opossum https://en.wikipedia.org/wiki/Virginia_opossum, despite its reputation as brainless, would be worth checking to see if in fact it is brainier than some bandicoots.
The fifth column from the left, Xenarthra (https://en.wikipedia.org/wiki/Xenarthra), refer to the ‘edentates’, an American group including armadillos (https://en.wikipedia.org/wiki/Armadillo), sloths (https://en.wikipedia.org/wiki/Sloth), and anteaters (https://en.wikipedia.org/wiki/Anteater). As readers can see, this clade has relatively small brains although not as much so as in the case of bandicoots.
The sixth column is diverse, apart from an African association common to most of them: elephants (https://en.wikipedia.org/wiki/Elephant), dugongs (https://en.wikipedia.org/wiki/Dugong), golden moles (https://en.wikipedia.org/wiki/Golden_mole), tenrecs (https://en.wikipedia.org/wiki/Tenrec), aardvarks (https://en.wikipedia.org/wiki/Aardvark), and elephant shrews (= sengis, https://en.wikipedia.org/wiki/Elephant_shrew).

These Afrotheria range from decephalised in e.g. tenrecs (which are both insular on Madagascar and extremely defended with e.g. spines) and dugongs, to encephalised in e.g. elephants. The most relevant aspect of Afrotheria in the current context is the fact that elephant shrews, although comparable with bandicoots, score higher than bandicoots in EQ.
The seventh column, Laurasiatheria, contains ungulates (https://en.wikipedia.org/wiki/Ungulate) and Carnivora (https://en.wikipedia.org/wiki/Carnivora) with fairly average brain size for mammals. However, it also contains other groups which include extreme values for EQ.

For example, pangolins (https://en.wikipedia.org/wiki/Pangolin) are included in Laurasiatheria, and they are decephalised in keeping with their extreme armour and their staple diet of ants and termites. At the other extreme we have dolphins (https://en.wikipedia.org/wiki/Dolphin), which surprisingly are in the same clade as pangolins and are so encephalised as to rival humans in EQ.
The eighth column shows Euarchontoglires, including primates, treeshrews (https://en.wikipedia.org/wiki/Treeshrew), rodents, lagomorphs (https://en.wikipedia.org/wiki/Lagomorpha), and colugos (https://en.wikipedia.org/wiki/Colugo). This clade shows the greatest range in EQ values of all the clades, going from colugos and hares at the bottom to the human species at the top.
Because primates – which specialise in braininess – greatly boost EQ in this clade, the authors have seen fit to present a ninth column for Euarchontoglires minus the primates. This shows that, without the primates, this clade would tend to have average EQ for mammals.
Many interesting patterns are revealed by this chart. However, one of them concerns the bandicoots.

What emerges is that the Peramelemorphia are unique, among mammals, in being a distinct clade with EQ always < 1.0. No other clade shows such consistency in EQ, and furthermore this consists of decephalisation without the usual associations of small brains such as armour, venom, extreme herbivory, etc.

When one thinks ‘primate’, it is fairly valid to think ‘brainy’ (although some of the extremely herbivorous lemurs may perhaps score < 1.0 in EQ, I need to check that). By the same token, when one thinks ‘bandicoot or bilby’ it is fairly valid to think ‘un-brainy’. I.e. if one had to pick the salient characteristic of bandicoots and bilbies, it would be that they are decephalised, rather than that they are marsupials.

There are many taxa of mammals, in six of the remaining seven major clades of mammals, that turn out to be even more decephalised than bandicoots, along the lines of rat-kangaroos (https://en.wikipedia.org/wiki/Rufous_rat-kangaroo and https://en.wikipedia.org/wiki/Musky_rat-kangaroo and https://en.wikipedia.org/wiki/Desert_rat-kangaroo), opossums, armadillos, tenrecs, manatees (https://en.wikipedia.org/wiki/Manatee), hippos (https://en.wikipedia.org/wiki/Hippopotamus), and colugos.

However, those decephalised mammals belong to clades that also extend to some degree of encephalisation (least so in Xenarthra).

In summary:
The range in values for EQ is great within any given clade of mammals, with a tendency to ‘outliers’ on both the positive and the negative sides of braininess. Whereas most naturalists are familiar with the braininess of certain mammals such as primates and dolphins, what deserves new appreciation is the 'unbraininess' of relatively unfamiliar groups, some of which are not just simply 'primitive'.

Putting off many other themes we could explore here, what emerges for now is a new view of bandicoots. These are not just a minor variant of marsupials. Instead, they are remarkable in their own right, in being the mammalian clade most specialised for limited EQ.

Ingresado el 21 de junio de 2022 por milewski milewski | 2 comentarios | Deja un comentario

Basic thoughts on amphibian body shapes

(writing in process)
Amphibians have three different shapes associated with three different orders: serpentine in Gymnophiona, lizard-like (and sometimes serpentine) in Urodela, and frog-like in Anura.
And the three orders of amphibians, with their extremely different body shapes, have different degrees of success in the world: frogs are extremely widespread, salamanders are largely restricted to the Northern Hemisphere, and caecilians are patchily and inconsistently distributed on three continents, mainly in the tropics.
What this means is that the serpentine amphibians, the caecilians, are so uncommon that even an ardent biologist might be forgiven for not even knowing that they exist.

Many people who stumble on caecilians actually take them for large earthworms, because they bear no resemblance to other amphibians, and are somewhat lost among the many convergently serpentine forms such as skinks, glass lizards, legless lizards, snakes, eels, and various serpentine salamanders. The serpentine salamanders are not widespread or common enough to alter the fact that serpentine amphibians are the exception rather than the rule.
Essentially, amphibians have a morphological spectrum of which the extremes are the leaping, long-legged typical frog on one side and the legless, serpentine caecilian on the other side. Both body forms are suited to both terrestrial and aquatic locomotion: frogs can both leap and swim using the same hindlegs, and caecilians can both slither on land and swim in the water (and burrow as well, as can the shorter-legged types of frogs).
Given this polarity and given the repeated evolution of the serpentine form in so many lineages of animals, in contrast with the fact that the anuran body form is restricted to frogs, my question is simply this: why has it been the frogs that are the common and widespread amphibians, rather than serpentine amphibians?
Imagine that, everywhere that frogs occur today, there are instead serpentine amphibians, with tiny or no legs. And the frogs are restricted to the out-of-the-way places where caecilians today live. In this ‘parallel universe’, when anyone says ‘amphibian’, what springs to mind is a snake- or worm-like animal because that is the most successful and predominant form of amphibian in most places.
I can easily imagine such a world, because

  • both the frog form and the serpentine form are about equally ‘bizarre’ or extreme as modifications of the generalised tetrapod body-plan seen in a typical salamander, and
  • we are already used to encountering other wormlike or serpentine animals everywhere, e.g. earthworms, snakes, small-legged lizards, etc.
    So that is the basic question: why is your common-or-garden amphibian not a caecilian?
    For example, the only amphibian found in southern African afrotemperate forest (e.g. near Knysna), away from water, is a dumpy little frog (Breviceps), about the most aberrant of frogs worldwide, that burrows and eats earthworms. Why would a caecilian not be even better-designed for that niche?
    One realm where no serpentine amphibian seems to venture is in the trees, where tree frogs are common. Frogs include many climbers, whereas no serpentine salamander or caecilian seems able to climb. However, it is hard to know how to interpret this. Is it really easier for a frog to climb than for a serpentine amphibian to climb? Frogs are hardly agile in the trees, are they?
    It is interesting that both frogs and snakes include big-mouthed forms that can swallow wide prey whole. Caecilians have small mouths, something that relatively few frogs (e.g. ant- and termite-eating Microhylidae) possess. However, again it is easy to imagine mother Nature having given caecilians an elastic, snake-like mouth, not so?
    One clue is that amphibians tend to run cool, and have a limited capacity bask. This means that they are generally less energetic than reptiles including snakes. Perhaps at these rather low body temperatures the serpentine body form is inherently less powerful or enduring than the frog body form?
    Amphibians have very sensitive skin; they need to avoid abrasion of that skin because of the microbial dangers; a worm-like shape requires a lot of contact with a surface and therefore abrasion risk during movement.

I think terrestrial caecilians depend on constructed burrows, i.e. on passages that they have excavated once for repeated use. And indeed caecilians are odd among amphibians in having dermal scales scattered under the epidermis.

Come to think it, the whole hopping locomotion, typical of frogs and toads, could be a way of minimising abrasion because it tends to get the animal over obstacles rather than through them. In the trees, even those tree frogs that do not hop can use their relatively long legs to minimise friction.

A novel concept for readers: a frog is not just a leaping animal but a friction-minimising one? And salamanders manage despite their large frictional surface, because they run so cold that they tend to be inactive compared with frogs?

(writing in progress)

Ingresado el 21 de junio de 2022 por milewski milewski | 0 comentarios | Deja un comentario

Salamanders vs skinks

(writing in progress) 
One of the most obvious similarities in the vertebrate world is the superficial similarity between lizards and salamanders.

Although this similarity is familiar, has anyone actually acknowledged how remarkable it is that a lineage of reptiles should be so similar to a completely unrelated lineage of amphibians? The resemblance is more one of convergent evolution than one of shared ancestry.
To help to explain what is remarkable, please consider bony fishes and cartilaginous fishes, which are separate classes of fishes. I do not know of any bony fish that would be confused, even at a glance, for any cartilaginous fish, or vice versa. However, skinks (Reptilia: Squamata: Scincidae) and salamanders (Amphibia: Urodela: e.g. Plethodontidae) belong to different classes too. And it would be easy to mistake one for the other at a glance, would it not?
Can readers think of any other examples of vertebrates in which the members of one class are similar enough in overall appearance to be confused with the members of another class?

I would not say that is true for e.g. dolphins and ichthyosaurs; they are too different-looking, despite being depicted in the textbook entries on evolutionary convergence.

Nor would I say that one could ever confuse a penguin with a seal or otter. They share some adaptations but remain different enough to be unmistakable as birds and mammals respectively, not so?

Sea snakes may resemble eels in the most superficial of ways but the body plans are quite different. The tail, for example, is long in eels and short in sea snakes, and the larval stages of eels are categorically different from anything seen among reptiles.
Since lizards are the more widespread group, it is normal to refer to lizard-like amphibians rather than salamander-like reptiles. But either of these ways of framing the similarity is worth thinking about. This is because of a strange quirk of global biogeography: that salamander-like reptiles are extremely widespread whereas salamanders are largely restricted to the Northern Hemisphere mainlands.
In this Post, I would like to begin to explore the incidence of skinks in particular, because to my mind they are the lizards most resembling salamanders. What I think this will show is that salamanders have by no means excluded skinks from their habitats, indicating that there is no real competition between skinks and salamanders. Therefore, one cannot explain the absence of salamanders from the southern lands and the Antilles as the result of their niches having been usurped by skinks.
Let us start in North America, the global headquarters for salamanders. The diversity and abundance of salamanders in the USA makes one’s head spin.

One would think that if skinks have been excluded by salamanders anywhere on Earth, it would be in North America. And yet such is not the case. Not only is there a decent radiation of skinks in the USA, but three species approach or cross the Canadian border.

Two good examples are Plestiodon fasciatus and P. anthracinus. Far from avoiding salamander habitat, Plestiodon anthracinus, found e.g. in western New York State, lives near springs and does not hesitate to take refuge in shallow water, going to the bottom and hiding under stones or debris while holding its breath! This is amphibious behaviour in a skink, and the point is that it is found in salamander habitat, not as a replacement for salamanders in some area not reached by salamanders.
I know that skinks reach Argentina. However, I have been unable to find out how far south this family reaches in South America. I have not yet tracked down any skink in Patagonia, but I will keep looking. It seems that skinks cut out at a certain latitude, so that no skinks make it into the coldest parts of South America. If so, this would be understandable, given that only a few skinks make it as far as Canada in North America. So in its own way South America again shows that there’s no tendency for the niches of salamanders to be usurped by skinks. This is because, in the case of Patagonia, neither salamanders nor skinks occur.
In New Zealand, again there seems to be a pattern in which skinks are mainly restricted to the North Island. There are plenty of species of skinks in northern New Zealand, which superficially resemble salamanders (which are of course absent from New Zealand).

Although geckos in New Zealand extend surprisingly far south, skinks do not seem to do likewise. This leaves the ‘salamander niches’ of the South Island empty, with neither salamanders nor salamander-like lizards, with the possible exception of certain aberrant geckos restricted to New Zealand - which are a whole topic of their own.
Salamanders and skinks have a superficial resemblance which breaks down on closer scrutiny.

I suspect that both lineages have similar diets. The fact that both lineages can autotomise and regenerate their tails is impressive, and both groups show some climbing ability and some affinity with water as a refuge. Both prefer cool conditions, the skinks being relatively cold-tolerant for lizards.

However, salamanders are more cold-tolerant than any skink (some salamanders being able to move slowly under freezing conditions, and most salamanders breeding in early spring whereas skinks presumably breed in summer), and the lesser aerobic capacity of salamanders than of lizards is indicated by the fact that most terrestrial species of salamanders in North America lack lungs completely.

There are also reproductive differences despite the internal fertilisation shared by the two lineages. Skinks copulate whereas salamanders go to remarkable lengths not to copulate, the female instead self-inseminating by picking up a spermatophore, deposited by the male during courtship, with her cloaca.

Of course, salamanders have larvae whereas skinks do not. Most salamanders lay eggs, while skinks at high latitudes give birth to active offspring. Salamanders tend to have toxic skins, whereas I know of no skink that has a toxic skin. Skinks, particularly the North American ones, go in for bright blue tails at the juvenile stage, distracting potential predators from the head. This is not a tactic familiar in salamanders.

Salamanders seem to live longer than skinks despite being the more fecund in terms of clutch/litter sizes.
Where do these findings leave us?
The picture emerging is that, despite their superficial similarities, salamanders and skinks do not seem to affect each other biogeographically. There is no evidence that the plethora of salamanders in North America has usurped the niches of skinks there. Although skinks occur in New Zealand, their presence there does little to explain the absence of salamanders. Skinks depend more than salamanders on warmth, as reflected by the greater latitudinal penetration of North America by salamanders than by skinks.
The bottom line for now is that the similarity between salamanders and skinks seem to have no explanatory power for the puzzle of northern and mainland restriction in the distribution of salamanders. The similarities between the two groups, while remarkable in their own way, seem to boil down to a single body shape being applied to two different ecological roles.

(writing in progress)

Ingresado el 21 de junio de 2022 por milewski milewski | 2 comentarios | Deja un comentario

Basking in amphibians

 (writing in progress) 

To understand amphibian ecology and biogeography, particularly the north/south difference in salamanders, it’s essential to bear in mind certain basic facts about amphibians in contrast to reptiles.

Reptiles, particularly lizards, bask./However, amphibians do not bask to the same extent. This is consistent with the moistness of the amphibian skin and the implied evaporative cooling.

Salamanders in particular do not bask. Frogs do bask in some cases but the function of basking differs from that in lizards.

Basking in frogs occurs mainly in two groups, viz

  • toads, and
  • tree- and reedfrogs.

In neither case can one assume that the function of basking is similar to that in lizards.

In toads, basking is possible because the skin is relatively dry. Certain Bufonidae of extremely high altitudes in the tropical Andes are extremely dark, which is presumably to enhance absorption of solar radiation. However, a basic difference between toads and lizards seems to be that after basking toads become less active, whereas after basking lizards become more active.

An implication emerges here: that even those amphibians that do bask do not use basking to boost muscle power or endurance.

The second group of frogs that bask is some of the various perching frogs (Hyperoliidae, Hylidae, presumably also Rhacophoridae), which sit still on branches or stems during the day. These frogs often expose themselves to full sunlight for many hours at a time, and rub waxy coatings on their skins to reduced evaporation so that they do not dehydrate in the process.

But here the odd thing is that their skins do not darken, as seen in lizards, to enhance the absorption of solar energy. Although climbing frogs are remarkably able to change colour (along the lines of chameleons), I have not heard of them darkening up (e.g. chameleons are pale by night and darker by day) while basking. If anything the opposite: some treefrogs are ghostly white by day, even to the degree of spoiling their crypsis/disruptive colouration and making them more conspicuous.

And again the climbing frogs do not use basking to boost muscular activity. Instead, they just keep sitting immobile until the sun goes down and the temperature falls. They are active in the cool conditions of dusk or night.

I am unsure why tree- and reedfrogs bask, but I suspect that it has to do with staying inaccessible to snakes. Although they make themselves somewhat obvious to birds by this self-exposure by day, they tend to be toxic enough to protect themselves from birds even if they are not aposematic.

(A frog is less likely to be found on a perch than on the ground, if only because for a snake to explore the branches is complicated and time-consuming, relative to the exploring the ground. Exploring the ground requires dealing with only two dimensions, so that odour trails can be easily followed. Exploring the branches means many backtrackings before a frog is discovered, whether by its odour trail or just by observation. And I do also think that birds in general would be less resistant to toxins, owing to the slow metabolism of snakes relative to birds. It’s hard to say whether birds would find it easier than snakes to discover tree frogs hiding among the branches and foliage.)

So although I have yet to see this stated directly in the literature, I suggest that amphibians do not bask in the same sense as reptiles, i.e. to boost muscular power and endurance. Amphibians do not seem to thermoregulate as such; instead they are passive reflections of environmental temperatures. And because they tend to be active at lower body temperatures than those seen in lizards, this makes sense overall in conjunction with the amphibian affinity for water and moist skin.

Tadpoles can stand body temperatures up to 34 degrees C for periods as long as they can cool down at night. It has been found in laboratories that, if tadpoles are kept at 34 degrees C (>3 degrees less than normal body temperature for humans), they die. However, if they are allowed to cool down for part of the diel cycle, they live (research by Amanda Niehaus).
An implication is that, whatever the salamander’s tail is used for, it is not basking.
So, w.r.t. the north/south question in salamander distribution:
Perhaps a useful perspective is that salamanders are essentially non-basking lizards, which are active mainly at night. I suspect that salamanders differ from geckos, which do not bask by day, by avoiding even the indirect basking used by geckos under cover. Geckos find warm places by day, e.g. under bark and roof tiles, to raise their body temperates. Although they are not active by day, they are the more ready to flee if encountered by predators breaking open their hiding places. I suspect that salamanders do not covertly bask in this way – but this needs to be checked in the literature.
Based on this framework, can readers see an explanation for the north/south discrepancy in the world distribution of salamanders?

Also see https://books.google.com.au/books?id=oaS-OpEjPtUC&pg=PA215&lpg=PA215&dq=basking+in+salamanders&source=bl&ots=N9hV9-SKYA&sig=2tHqu1CUK8Q8NX8xzgWlgvN9KKo&hl=en&sa=X&ei=6tYEVd27CYnN8gWAjoKAAQ&ved=0CC0Q6AEwAg#v=onepage&q=basking%20in%20salamanders&f=false

 (writing in progress) 

Ingresado el 21 de junio de 2022 por milewski milewski | 0 comentarios | Deja un comentario