25 de junio de 2022

Spinescence in the pea genus Astragalus, part 2

(writing in progress)

The following makes sense once one becomes familiar with it. However, it is a permutation of spinescence that I did not dream of until I encountered it for the first time recently. This was one of those moments of ‘I wish I thought of that’ in the game of imagining ‘evolutionary options’ out of thin air.
Astragalus creticus is a hummock-like or cushion-like shrub associated with intensive grazing by domestic livestock for centuries, or more likely millennia, on the island of Crete.

It is no surprise that, being a pea (Fabaceae), the species has pinnate leaves that are drought-deciduous. And it is also no surprise that it is spinescent. Peas, after all, are often spinescent. Furthermore, drought-deciduous plants with pinnate leaves tend also to be spinescent in various families.
The surprises come in

  • the organ from which the spines are derived (namely the rhachis), and
  • the three-phase deployment of the spines, first as a foliar spine, then as a nodal spine, and finally as a caular spine.

It is unusual enough for a given plant species to possess more than one category of spine. But I have never previously encountered a plant that manages to pull off this combination using a single, versatile structure (by means of an ontogenetic shift).

And this, on reflection, seems such a good idea that immediately I find myself asking the following question:
Why would this pattern be restricted to Astragalus, and (as far as I know) absent from any plant in, for example, Australia?
My preliminary answer is that Astragalus – and particularly this species - represents an extreme of adaptation on Earth. Its habitat has been subject to intensive and consistent herbivory for millennia on what, by Australian standards, is a nutrient-rich substrate despite the stoniness.

Herbaceous plants have adapted to this sort of extreme herbivory by forming thistles. However, low shrubs have adapted equally extremely by using foliar spinescence in a different way.

Both thistles (which are unimaginably species-rich in the Mediterranean Basin although belonging mainly to the Asteraceae) and Astragalus derive spines from the leaves. However, what Astragalus does that is so novel to me is to use the rhachis in a way unfamiliar in any other plant.

The elegance of this adaptation lies in its simplicity: merely a functional shift by means of ontogeny, with a minimal shift in the form of the spine itself.
There may be parallels with Aciphylla in New Zealand, but I suspect that even that analogy may be limited.
Using the rhachis-tip as a foliar spine would be novel enough. But then keeping this rhachis after the leaf has died (or at least ceased to photosynthesise) on slow-growing stems with compressed internodes, and thus converting it into a nodal spine, is something akin to a ‘stroke of genius’ of Nature.

And then, just in case any really tough-minded ungulate (such as the donkey) gets it into its head to bite off a whole stem-system, the same spines can be retained as caular spines.

And all of this works because the plant, at the same time, adopts such a compact and ground-hugging form that herbivores have minimal access to the surfaces of the plant.
All of this certainly amounts to some sort of ‘Guinness record’ in the annals of anti-herbivore defences in plants. But an even more intriguing possibility is that Astragalus creticus has gone beyond defensiveness (fence-mindedness), to convert itself into something resembling a ‘pea-lawn’.

What I mean by this is a fabaceous plant that facilitates herbivory by ‘fencing off’ its precious shoots while allowing access to its leaves. Although so defensive, it may in some sense be ‘encouraging’ herbivory, as a means of competing with other plants in the indirect way grasses so often do. The hypothetical result is the management of herbivores so that they do not destroy its capacity to replace eaten leaves.

Please note that some photos show that A. creticus can virtually dominate the vegetation over small areas.
Please also bear in mind that Astragalus is well-known for its chemical defences, such as glycosides and selenium. The genus is valuable medicinally because of its toxins. And, if A. creticus retains such chemical defences, then it might be defended in an even more complex way than I portray here in the form of spines.
So my question is: is Astragalus creticus merely one of the most extremely defended plants anti-herbivory, in a habitat that is extremely herbivorous? Or is it the dicotyledonous equivalent of a shrub-gone-lawn, taking a principle seen in e.g. Vachellia and shifting it to such an extreme that it is hardly recognisable at first?  
The following shows the foliage of Astragalus creticus in what I assume to be the rainy season in this Mediterranean climate.

In the following view of the foliage, the plant hardly looks spinescent.

The following shows the extreme growth-form taken by this species, which forms cushions or hummocks presumably in adaptation to an intense regime of herbivory by domestic livestock.

The following shows the plant in what I take to be the dry season (the Mediterranean summer) when the pinnae have fallen off. The plant certainly looks more twiggy than in the green season but even her its spinescence is not at first obvious.

The following close-up of the foliage shows the curved spines, which turn out to be derived from the rhachis.
The following close-up shows that the green leaf has a sharp tip to the rhachis, which is somewhat green while the pinnae are green. If one accepts this rhachis tip as a spine, the obvious classification of this form of spinescence is foliar spinescence.
The following again shows the foliar spinescence in Astragalus creticus, the spine being an essentially green rhachis-tip turned ‘pungent’.

The following is what I take to be new growth, in autumn just after the arrival of the rains. Shoots are growing among the non-green spines, which makes these spines nodal spines. The big surprise is that these nodal spines are the very same spines seen above as foliar spines. The rhachis has been converted from a foliar spine into a nodal spine by the tactic of persisting after its pinnae have fallen, and retaining its spinescence once its green hue has faded. I do not know whether these spines remain alive, but this need not matter for its defensive function.
The following close-up again shows what are here functionally nodal spines, but what turn out to be persistent rhachises.
The following shows that the persistent spinescent rhachises persist way down the stem, which means that they persist for years in such a slow-growing shrub. This means that – wait for it – the same rhachis has now been converted to a caular spine!
The following two botanical paintings suggest that the caular spines can be green even low down on the stems, but I doubt this and I suspect that this botanical painting is inaccurate in this respect.
Here we have the caular spines depicted as non-green, which I suspect to be the truth.
The following two photos show again what the leaf is like when it first appears: it is a fairly normal pinnate leaf, typical of so many peas, except for a ‘pungent’ rhachis-tip that is probably more easily felt than seen.


(writing in progress)

Ingresado el 25 de junio de 2022 por milewski milewski | 0 comentarios | Deja un comentario

Spinescence in the pea genus Astragalus, part 1

(writing in progress)

I have known spinescent peas (Fabaceae) for more than half a century. This started in the Fynbos Biome in South Africa, where various spp. of e.g. Aspalathus (typically ‘fireweeds’ in nutrient-poor, fire-prone, semi-sclerophyllous vegetation) are foliar-spinescent.

And of course I well know various spinescent mimosas such as Vachellia, with their stipular or epidermal spines.

However, it was for the first time in my life that I recently encountered a new configuration of spinescence in legumes - and indeed an unusual configuration of spines for any lineage of plants.

I refer to a spinescent rhachis, and what is more, in some cases, a spinescent rhachis that persists as a functional spine after the pinnae are shed.
Now that I have encountered this form of spinescence, it seems so obvious that plants would have this configuration of physical defence available to them. But I have never seen it before as far as I can recall.
Astragalus is the largest genus of plants on Earth, containing perhaps up to 3000 spp. in Eurasia, North and East Africa, and the Americas. Iran alone has about 850 spp. In the checklist of spinescent plants of Israel (), there are seven spp., all of which I show below.
Astragalus sharpens the mind about the nature of spinescence. This is because it is so novel from the perspective of a plant ecologist based in fynbos, kwongan, or any other type of vegetation in Australia or New Zealand.
I have only just begun my learning curve with this genus, and it may turn out that there are several different forms of spinescence in Astragalus. The form for which I have evidence is the spinescent rhachis, and even this one form has already proven to be somewhat complicated/multi-facetted.
As far as I have been able to establish so far, all spp. of Astragalus have pinnate leaves. However, some (perhaps several hundred spp. in total) have converted the tip of the rhachis into a spine. Since the rhachis is part of the leaf, this would, at first glance, seem to qualify as a foliar spine.
For a start, I find this phenomenon new to me: the rhachis-tip as spine.
I have encountered many plants with foliar spines, and the configurations are varied. But in general I have not regarded the typically pinnate leaves of peas (Fabaceae) as candidates for foliar spinescence. This is because it is in the nature of the typical pea leaf that it is soft, non-sclerophyllous, and defended by toxins rather than lignification and ‘pungency’.

Yet here, in Astragalus, we find that counterintuitive combination, the pinnate-pea leaf made spiny, without lignification (sclerophylly) of the leaf-blades themselves. Because the rhachis functions mainly as a structural support (any photosynthesis in the rhachis being a subsidiary function), it is ‘pre-adapted’ to be rigid even in those plants lacking any sclerophylly, such as the kinds of plants living in ecosystems capable of supporting dense populations of herbivores.
In Australia, there is noteworthy genetic plasticity in the pea genus Bossiaea, with several different types of spines in various spp. And Bossiaea does occupy some relatively nutrient-rich, relatively fire-free habitats such as the margins of salinas, where it has converted the twig-tips into green spines. However, even Bossiaea has not come up with the idea of a spinescent rhachis.
Part of the explanation for the unusual evolution of a spinescent-tipped rhachis in Astragalus seems to be the overall form of the shrub, which tends to be hummock-like in partial convergence with e.g. Australian hummock grasses (Triodia). The hummock form, combined with the hedgehog-like armature of spinescent rhachises projecting from the foliar surface, makes for an effective defence against herbivores in phrygana- or batha-type vegetation. This is the sort of vegetation that has been grazed to within an inch of its life for thousands of years in the overgrazed semi-arid ‘pastures’ of the Middle East.
So here we have a syndrome of spinescence quite different from any we see in Australasia, and associated with the ungulate fauna of the Northern Hemisphere.
In my comparisons of the Australian flora with that of the Fynbos Biome in South Africa, I have noticed that the peas show foliar spinescence even where few other plants show foliar spinescence. So, the fact that Astragalus, being a genus of peas, is foliar-spinescent is not that surprising to me.

However, it is the nature and derivation of these spines, plus the hummock form of the spinescent spp. of Astragalus, that is new to me. This provides some sort of parallel with my comments, in another Post, re the plumbaginaceous genus Acantholimon, which seems convergent with Astragalus in Israel in its combination of a cushion form and foliar-spinescence.
Please note that there are cushion-like plants in Australia. However, but as far as I know these are not foliar-spinescent. They thus differ from Acantholimon and Astragalus in e.g. Israel. In the case of New Zealand, one possible parallel lies in the apiaceous genus Aciphylla, with which I am not familiar.

There are hummock plants in Australia, but they tend to be pyrophilic grasses with foliar-spinescence, not pyrophobic peas with foliar spinescence as in the case of Astragalus in Israel. And there are foliar-spinescent peas in Australia, but these do not have the rhachis as the spinescent plant-part as in Astragalus in Israel.
Given that the rhachis is a kind of leaf-stem, and that it is a relatively non-photosynthetic part of the leaf, is a spinescent rhachis truly part of the leaf, functionally, or should it rather be regarded as a kind of spinescent stem? I am unsure.

I have observed in photos that the spinescent part of the rhachis, in some spp. of Astragalus, is non-green, much like a stipular spine in acacias. Furthermore, in some spp. of Astragalus there seems to be a pattern in which the rhachis is initially green, but persists in non-green form after the pinnae are shed.

Normally in peas and other legumes, when a pinnate or bipinnate leaf is shed, the rhachis is shed as well as its pinnae or pinnules. However, in some spp. of Astragalus, the shedding seems confined to the pinnae, the rhachis remaining as a spine functionally similar to a non-green stipular spine.

I do not know if such non-green, persistent rhachises, functioning as spines, are dead or alive. But in any species of Astragalus in which the main spinescent function of the rhachis is performed after the pinnae have fallen, I would tend to consider this as a form of nodal spinescence rather than foliar spinescence.

So, my current thinking is that the genus Astragalus does contain both foliar spines and nodal spines. However, as far as I know the seven Israeli spp. of spinscent Astragalus are all foliar-spinescent.
The following outlines the biogeography of genus Astragalus:

The following shows the pinnate leaves of a non-spinescent species of Astragalus. The rhachis is not as bright a shade of green as the pinnae, but it is functionally part of the leaf.
The following paper describes Astragalus orientopersicus of Iran:
The following excerpt from the above paper, describing the leaves of A. orientopersicus, shows how unclear the typical botanical description is w.r.t. the origin and nature of the spines. Here we have confusion between the petiole and the rhachis, and the word ‘pungent’ is used instead in description of the pinnae, which I doubt are actually spinescent. In the abstract of the paper, the rhachis is clearly described as spiny, but in the body of the paper, i.e. in the full description, this simple fact gets garbled by ambiguous wording.

What the author of the above taxonomic paper does not seem to mention is a feature evident in the photos he himself uses in his paper: the green rhachis in this species tends to lose its pinna but remain attached to the plant as what is effectively a green spine.
The following sp. (Astragalus humillimus) of semi-arid Colorado has spinescent ‘petioles’, which seem likely to be the spinescent rhachis retained after the pinnae are shed.

The following close-up of Astragalus humillimus of the USA shows the non-green rhachis acting as a spine, presumably after the pinnae have been shed and the originally greenish rhachis has lost its chlorophyll. I have not yet noticed this pattern of spinescence in any of the spinescent spp. of Astragalus in Israel (see below), and I would tend not to classify the spinescence of A. humillimus as foliar spinescence despite the fact that it is the rhachis that is spinescent and the fact that the rhachis is certainly part of the leaf.


The following material all illustrates the various spinescent spp. of Astragalus occurring in Israel.
Astragalus angustifolius, which forms hummocks:
Astragalus angustifolius showing the spinescent rhachis of the pinnate leaves. In particular, please note that a) the spine of the rhachis hardly projects beyond the pinnae, and b) even the spine of the rhachis remains green. Hence I can catgorise this as foliar spinescence despite this being such a different configuration of spinescence from any of the other foliar spines that I’ve mentioned in the Australian flora. Astragalus has come up with foliar spines of a quite new kind, relative to its pea relatives in Australia, relative to all cushion- or hummock-like plants in Australia, and indeed relative to all plants in Australia. I associate this with the selective pressures exerted by dense populations of ungulates in the habitats of Astragalus.

The photos of Astragalus bethlehemiticus in https://flora.org.il/en/plants/astbet/ show clearly enough that it is the long rhachis that ends in a spine.
Astragalus cephalotes: https://www.youtube.com/watch?v=92xnhr5oh3U seems not to have a growth-form similar to a cushion or hummock. It is listed in the Israeli website as having spinescent leaves, but I have yet to figure out exactly where the spines are.
Astragalus cephalotes:

Astragalus coluteoides:
Astragalus coluteoides:

Astragalus coluteoides, showing the spinescent rhachis. Again, I have little hesitation in categorising this as foliar spinescence, because the spine itself remains basically green.

Astragalus cruentiflorus:
Astragalus cruentiflorus, showing spinescent rhachis. In this case, the spiny tip of the rhachis does project some way beyond the pinnae, and it has lost its green colour. However, I would still be inclined to categorise this as foliar spinescence rather than nodal spinescence.

Astragalus cruentiflorus, showing spinescent tip of rhachis, close-up.

Astragalus cruentiflorus, showing hummock shape of shrub. I do not know of any Australian pea that adopts this growth-form, less still one that is foliar-spinescent, less still one that uses the rhachis tip as the spine.
I have yet to make out the exact nature of the spinescence in the Israeli species Astragalus deinacanthus:
The following illustrates Astragalus echinus:
The following illustrates Astragaus gummifer:

(writing in progress)

Ingresado el 25 de junio de 2022 por milewski milewski | 0 comentarios | Deja un comentario

Recrudescence of foliage, with particular reference to acacias

@arthur_chapman @abedggood @mattbarrett @iancastle @jeremygilmore @alan_dandie @tonyrebelo

Many lineages of woody plants have ’juvenile foliage' different from the foliage of adult/mature individuals. This is an example of heteroblasty (https://en.wikipedia.org/wiki/Heteroblasty_(botany)).

 However, there may be two different phenomena conflated here.

The first is true juvenile foliage, seen in seedlings and, in some cases, also saplings. The second is what I would prefer to call ‘recrudescent foliage’, which can appear even in old plants when they are damaged.
An example of recrudescence (https://www.merriam-webster.com/dictionary/recrudescence) is needle-leaf foliage in Cupressaceae (https://crataegus.com/2015/07/01/juvenile-growth-on-junipers-cut-leave-alone/ and https://www.kusamurabonsai.org/articles/juvenile-and-mature-juniper-foliage/#:~:text=Juniperus%20procumbens%20%27Nama%27%20is%20a,take%20care%20of%20a%20bonsai.).

Members of this family are well-known to be able to live for centuries. However, if a mature plant - with its mature foliage of adpressed, scale-like leaves - is damaged, then the regrowth can be composed of needle-like leaves, in some cases foliar-spinescent. Since the plant is so old, does it not seem misleading to use the term ‘juvenile’ to describe this foliage?
The genus Acacia (https://www.inaturalist.org/observations?taxon_id=47452) is also worth considering, as follows.
Acacia contains many spp. bearing phyllodes (https://en.wikipedia.org/wiki/Phyllode) instead of leaves. All of the phyllodinous spp. have juvenile foliage in the strict sense (i.e. in seedlings, https://www.sciencedirect.com/science/article/abs/pii/S0015379617301270 and https://upload.wikimedia.org/wikipedia/commons/6/68/Acacia_facsiculifera_seedling.jpg).

However, a noteworthy feature of this genus is that few spp. have recrudescent foliage, in sharp contrast to ecologically related lineages with convergent foliage, such as eucalypts (https://en.wikipedia.org/wiki/Eucalypt).

What I call recrudescent foliage is one of the most consistent and ecologically important features of eucalypts (https://www.castlemaineflora.org.au/pic/e/eucal/jleaf/jleaf.htm and https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1926.tb06691.x and https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/0012-9658%281999%29080%5B1944%3AJFATSO%5D2.0.CO%3B2).

However, the genus Acacia, which coexists with eucalypts in most habitats of eucalypts, seems generally devoid of recrudescent foliage even in the spp. that grow into fairly tall trees. So, in Acacia, the well-known juvenile foliage is something quite different from the sort of foliage usually called juvenile foliage in the case of eucalypts.
One species of Acacia, namely A. melanoxylon, is known to possess recrudescent foliage. However, this species is also rather extreme in its genus in being a particularly tall tree, associated mainly with fire-free situations, growing even within rainforests in its natural state, and being widely planted for its timber.
Even In a genus of acacias such as Vachellia (https://en.wikipedia.org/wiki/Vachellia), there is a difference among juvenile (seedling) foliage, recrudescent foliage, and mature foliage.

The mature foliage is virtually non-spinescent (https://www.inaturalist.org/observations/61102835 and https://www.inaturalist.org/observations/11165998), where it outgrows the reach of even giraffes. This applies also to unpruned saplings in gardens, that have been protected from mammalian herbivores. However, the recrudescent foliage is extremely spinescent, the spines being non-photosynthetic stipules (https://www.shutterstock.com/de/image-photo/vachellia-xanthophloea-acacia-tree-close-thorns-1550994515 and https://www.inaturalist.org/observations/122965582).

The spines, although not green, are technically part of the foliage in a way not true for nodal-spinescent plants. This is because the stipule is technically part of the leaf - in the broad sense of leaf including both the hyperphyll (https://en.wiktionary.org/wiki/hyperphyll) and the hypophyll (https://en.wiktionary.org/wiki/hypophyll).

So, the leaf-stipule complex in Vachellia, which consists of a bipinnately compound leaf and its spiny stipule, is a kind of homologue for what is usually called a ‘juvenile’ leaf on a mature eucalypt that has been damaged.
It may seem far-fetched to compare the leaf-stipule complex in Vachellia with the ‘juvenile’ leaf of a eucalypt. However, I would point out that so-called juvenile leaves in eucalypts (which I prefer to call recrudescent leaves) are more than just differently-shaped from adult/mature leaves on the same individual plant. The differences lie not just in the shape and size of the leaf-blade, but also in the presence/absence of a petiole, the arrangement about the axil (i.e. whether opposite or alternate), the surface-texture, and the chemical defences. In many eucalypts, the so-called juvenile foliage is so distinctive that it would seem to belong to a different species from the adult/mature foliage.

There seems to be analogy with this in Vachellia. However, a difference is that it is mainly the stipular part of the hyperphyll-hypophyll complex that is subject to change in the phenomenon of foliar recrudescence.
Some spp. of phylllodinous Acacia possess stipular spines. So, I wonder whether these spp., like Vachellia, can actually outgrow the stipular spines when the shrub/small tree becomes too tall to be defoliated by its main mammalian herbivores. No student of Acacia seems to have had this search-image in mind, possibly because of the vagueness implicit in the usual term ‘juvenile foliage’.

Given the current use of the term ‘juvenile foliage’, it may not have occurred to any botanist to ask

  • why do most spp. of Acacia, beyond the seedling stage, lack ‘juvenile’ foliage even if damaged? or
  • is the stipular spine in Acacia functionally part of the foliage, or part of the stem system?

Bipinnate leaves occur in the seedlings of – as far as I know – all of the hundreds of phyllodinous spp. in the genus Acacia. When an adult individual Is damaged, most spp. do not revert to the divided leaf of the seedling. I have found this puzzling, because

  • many eucalypts have an extremely well-developed pattern of recrudescence when damaged, and
  • the phyllodes of some spp. of Acacia are convergent with the adult leaves of eucalypts.

One possible explanation for this overall difference between Acacia and eucalypts invokes the following differences between the genera in other aspects of their ecology and life history.

Firstly, most spp. of Acacia are shorter at maturity (being tall shrubs or short trees) than most spp. of eucalypts. Even mallee eucalypts are substantial relative to coexisting Acacia spp., owing to the development of lignotubers in the eucalypts with no counterparts among even those spp. of Acacia (e.g. A. rostellifera, http://worldwidewattle.com/speciesgallery/rostellifera.php) that profusely sucker (https://en.wikipedia.org/wiki/Basal_shoot).

Secondly, Acacia tends to be short-lived despite having dense wood. In many species, senescence sets in after only a few decades of life. This combination of limited body size and limited lifespan, together with a capacity to fix atmospheric nitrogen, may mean that there is comparatively little advantage in developing a particular form of foliage during vegetative regeneration. Acacia tends to respond to wildfire by dying and recovering germinatively.
It may shed light on these questions to examine some of the few spp. of Acacia that do possess recrudescent foliage.

One is A. melanoxylon, as mentioned above. The other is Acacia adunca (https://en.wikipedia.org/wiki/Acacia_adunca and http://worldwidewattle.com/speciesgallery/adunca.php and https://www.anbg.gov.au/gnp/gnp9/acacia-adunca.html and https://www.anbg.gov.au/gnp/gnp9/acacia-adunca.html), which is a tall shrub or short tree (maximum height 7 m) restricted to a small area around the border between New South Wales and Queensland. Acacia adunca is cultivated extensively in New Zealand, where it is known as Golden Glory.
Holiday (1974), page 8, states of A. adunca: “the feathery true leaves persist for some time on young trees and return when the tree is cut.” This seems to indicate both that the juvenile (seedling) foliage persists into the sapling stage, and that what I call recrudescence occurs in this species, and perhaps also its closest relatives within the genus Acacia, viz.

Given that ‘juvenile’ poorly describes the post-seedling heteroblasty discussed above, can readers improve on my suggested new term of ‘recrudescent’ for the foliage in question?

Ingresado el 25 de junio de 2022 por milewski milewski | 1 comentario | Deja un comentario

Foliar-spinescent Acacia maitlandii, an associate of foliar-spinescent hummock grasses

@arthur_chapman @abedggood @mattbarrett @iancastle @jeremygilmore @alan_dandie @tonyrebelo

Foliar-spinescent grasses in the genus Triodia (https://en.wikipedia.org/wiki/Triodia_(plant)) dominate the vegetation over large areas in semi-arid Australia. Various spp. of Acacia are associated with Triodia (see https://www.inaturalist.org/journal/milewski/67576-to-what-extent-do-foliar-spinescent-acacias-coexist-with-foliar-spinescent-grasses-in-central-australia).
Essentially, Acacia can occupy three different types of niche in vegetation dominated by Triodia, as follows.

  • Acacia can be somewhat like a woody version of a ‘fireweed’, growing rapidly after intense fire combusts the hummocks of Triodia, and then dying after a few years as the Triodia once again usurps its space. My impression that these short-lived spp. of Acacia tend to be neither foliar-spinescent nor particularly flammable. They are essentially successional to Triodia in the fire-cycle. The seeds tend to be hard, capable of remaining dormant for decades.
  • Acacia can take over with the senescence of the hummocks of Triodia in the absence of fire. Although Triodia is ‘designed to burn’, it can happen that a given stand somehow evades being burnt for several decades. In such cases the hummock grass tends to lose vigour, and shrubs or low trees of Acacia tend to increase at the expense of the grass, simultaneously reducing the flammability of the whole vegetation. I suspect that most spp. of Acacia in this category are not foliar-spinescent.
  • Acacia can co-occur with the hummocks of Triodia as a minor component of the mature vegetation. The species in focus in this Post, namely Acacia maitlandii (https://www.inaturalist.org/taxa/926523-Acacia-maitlandii and http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&name=Acacia_maitlandii), is an example. This species happens to be foliar-spinescent, paralleling Triodia in this way.

Acacia maitlandii (https://en.wikipedia.org/wiki/Acacia_maitlandii and https://florabase.dpaw.wa.gov.au/browse/profile/3434) is

Acacia maitlandii accompanies Triodia merely as a sparse, low ‘upper stratum’. It has a lignotuber/roostock of sorts, which means that it can regenerate vegetatively after wildfire, provided that the combustion is not intense. The seeds of A. maitlandii are relatively soft, distinguishing it from the many 'hardseeded' species of Acacia.
Judging from the form of its elaiosome, A. maitlandii is dispersed and sown by ants, which is consistent with a semi-pyrophilic niche (http://worldwidewattle.com/speciesgallery/maitlandii.php).

There are many spp. of Acacia with spinescent phyllodes. However, A. maitandii seems to be among the most strongly spinescent spp. in the genus. Its phyllodes vary in shape but are always spinescent (https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Acacia~maitlandii and http://worldwidewattle.com/speciesgallery/maitlandii.php).
An odd feature of A. maitlandii is that it has resinous twigs, presenting another possible parallel with Triodia (various spp. of which are also resinous). I presume that one of the functions of the resin in A. maitlandii is to deter herbivores, but I do not know if – as in the case of Triodia – it also promotes flammability.

I know of few foliar-spinescent plants, other than spp. of Triodia, which combine resinousness with foliar-spinescence. Therefore, this combination in A. maitlandii deserves further investigation.
The following shows the ‘pungent’ tips of the sclerophyllous phyllodes of Acacia maitlandii: https://en.wikipedia.org/wiki/Acacia_maitlandii#/media/File:Acacia_maitlandii_flowers_and_foliagee.jpg and https://www.inaturalist.org/observations/91523066 and https://www.inaturalist.org/observations/121559495 and http://worldwidewattle.com/speciesgallery/descriptions/pilbara/html/maitlandii.htm.
The following show that the shape of the phyllodes varies within A. maitlandii: http://worldwidewattle.com/speciesgallery/images/maitlandii.jpg and https://apps.lucidcentral.org/wattle/text/entities/acacia_maitlandii.htm
The following show that the crown of A. maitlandii tends to be rather sparse: https://en.wikipedia.org/wiki/Acacia_maitlandii#/media/File:Acacia_maitlandii.jpg and https://www.inaturalist.org/observations/9158107.
The following shows the coexistence of A. maitlandii with Triodia: http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&name=Acacia_maitlandii.

Ingresado el 25 de junio de 2022 por milewski milewski | 2 comentarios | Deja un comentario

24 de junio de 2022

Acacia estrophiolata exemplifies an unusual type of heteroblasty: juvenile form within phyllodinous foliage

@arthur_chapman @abedggood @mattbarrett @iancastle @jeremygilmore @alan_dandie @tonyrebelo

In Acacia, many species have phyllodes (https://en.wikipedia.org/wiki/Phyllode) - derived from ancestral petioles - instead of leaves.

For most naturalists familiar with these plants, 'juvenile foliage' means the reversion to pinnate leaves that occurs in seedlings and, sometimes, on shoots regenerating from damage on saplings (https://www.flickr.com/photos/handsoff/44327173262 and https://wellcomecollection.org/works/mfrr2th3/items and https://keyserver.lucidcentral.org/weeds/data/media/Html/acacia_melanoxylon.htm and https://keys.lucidcentral.org/keys/v3/eafrinet/weeds/key/weeds/Media/Html/Acacia_melanoxylon_(Australian_Blackwood).htm).

However, it may be news to most naturalists that, in at least one species of Acacia, even the phyllodinous foliage itself changes from a juvenile form to a mature form as the plant grows from sapling to adult.

This can be described as a heteroblastic pattern (https://en.wikipedia.org/wiki/Heteroblasty_(botany)) within the phyllodinous foliage. The ‘juvenile’ foliage of phyllodes (https://en.wikipedia.org/wiki/Phyllode) differs greatly from ‘adult/mature’ foliage of phyllodes.

This difference may also involve foliar spinescence, in which the phyllodes have ‘pungent’ tips (https://www.wordnik.com/words/pungent#).

Acacia estrophiolata (http://www.aridzonetrees.com/assets/acest07.pdf and https://en.wikipedia.org/wiki/Acacia_estrophiolata and https://apps.lucidcentral.org/wattle/text/entities/acacia_estrophiolata.htm and https://spapps.environment.sa.gov.au/SeedsOfSA/speciesinformation.html?rid=140 and http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&name=Acacia_estrophiolata) is a small tree occurring in central Australia.

In maturity it has pendulous foliage typical for a wattle, with long, narrow, non-spinescent phyllodes.

However, when the growing plant is still shrub-size, the foliage is surprisingly different. The phyllodes

  • have different aggregation and orientation to that seen in maturity, and
  • may be spinescent, although I have yet to find a clear statement that the tips of the phyllodes are ‘pungent’.

In maturity A. estrophiolata can reach as high as 15 m, making it one of the taller trees of semi-arid central Australia. The wood is ‘very hard’ (Latz 1995), which suggests to me a wood density >1.1.

This is a relatively slow-growing and long-lived species among wattles, as opposed to a ‘fireweed’ or a short-lived, successional species. There is an implication that, because growth is slow, herbivory in the sapling stage can be a particular problem for this species.
What is clear is that A. estrophiolata varies greatly in foliage ontogenetically, as it increases in height above ground. This seems to be partly explained by its palatability to large herbivores.

However, I have yet to find a clear statement of the height-threshold at which the form of the foliage switches. My impression is that this is at about 3 m. If so, this is evolutionarily puzzling because no indigenous herbivore in the habitat of A. estrophiolata can reach higher than 2 m.

The anti-herbivore defences of A. estrophiolata present the same puzzle as for so many other plants in Australia: which herbivores were originally being defended against?

The literature fails to distinguish between kangaroos and introduced ungulates. However, A. estrophiolata is regarded as among the more palatable of the wattles of semi-arid central Australia.

Contrast this with e.g. Acacia maidenii (see my other Post), which is certainly foliar-spinescent. That species, which is more strongly associated with Triodia and never grows taller than 3 m, is regarded as unpalatable to the degree that it is never eaten by large herbivores.
Peter Latz (1995, page 97) states of A. estrophiolata:
“The narrow leaves [sic] are dense and pendulous, giving the tree a willow-like appearance. Juvenile plants, with wider, shorter, spiny leaves [sic], are quite different in appearance to the adult trees. (This juvenile foliage is often never lost when the trees occur in the harsher spinifex country.)”

However, I do not understand the relationship of A. estrophiolata to fire. This is because Latz describes this species as fire-intolerant, stating “This extremely drought-tolerant tree is often killed or at least severely affected by fire.” My confusion arises because 'spinifex country' is associated with wildfire.
Acacia estrophiolata is an extreme example of heteroblasty in its genus. This may be partly because it combines unusual palatability with unusually slow growth, in a semi-arid environment. However, the question of foliar spinescence in the juvenile-form phyllodes needs further investigation.
Acacia excelsa (https://www.inaturalist.org/taxa/139917-Acacia-excelsa) is closely related to A. estrophiolata. It would be worth checking whether it shows the same heteroblastic pattern as seen in A. estrophiolata.
The following shows the height and form of the mature (adult) plant in Acacia estrophiolata: http://www.flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?form=speciesfacts&name=Acacia_estrophiolata and http://www.aridzonetrees.com/acacia-estrophiolata.html.
The following shows that the mature/adult phyllodes are not spinescent: http://worldwidewattle.com/speciesgallery/estrophiolata.php and https://en.wikipedia.org/wiki/Acacia_estrophiolata#/media/File:Acacia-estrophiolata-foliage.jpg and https://www.wikidata.org/wiki/Q4670928#/media/File:Acacia-estrophiolata-habit.jpghttp://worldwidewattle.com/speciesgallery/images/estrophiolata.jpg 
The difference in form between the ‘juvenile’ and the mature/adult form of the foliage of A. estrophiolata is indicated by the use of the term ‘spiky’ in http://worldwidewattle.com/speciesgallery/estrophiolata.php?id=3327.

The following relates the defensive ‘juvenile’ form of the foliage to the palatability of A. estrophiolata, presumably invoking domestic ungulates: https://web.archive.org/web/20080709022239/http://www.fao.org./ag/agp/agpc/doc/Gbase/new_grasses/acaest.htm.
There are few photos of the ‘juvenile’ foliage of A. estrophiolata on the Web, and all are only tentatively identified: https://bie.ala.org.au/species/https://id.biodiversity.org.au/node/apni/2898101 and https://www.inaturalist.org/observations/98461582 and https://www.inaturalist.org/observations/103872799 and https://www.inaturalist.org/observations/96854190 and https://www.inaturalist.org/observations/96081669.

I am puzzled because these phyllodes, although stiff, do not look spinescent. This seems to contradict the adjectives ‘spiky’ and ‘spiny’ used by several authors to describe this foliage.
The following photo, of a specimen cultivated in Arizona, shows the contrast in foliage-form within A. estrophiolata: http://www.aridzonetrees.com/assets/acest07.pdf.

The overarching puzzle, in this whole field of research, remains:
which herbivores exerted major evolutionary pressure on the foliage-form?

Ingresado el 24 de junio de 2022 por milewski milewski | 2 comentarios | Deja un comentario

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

@arthur_chapman @abedggood @mattbarrett @iancastle @jeremygilmore @alan_dandie

Australia is the continent on which foliar spinescence is best-developed (http://ianfrasertalkingnaturally.blogspot.com/2020/06/spinifex-prickly-heart-of-australia.html).

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 (https://inaturalist.ala.org.au/taxa/132351-Triodia), 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

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’.

Acacia tetragonophylla

  • relies on germination to regenerate, but also grows slowly, and
  • is extremely drought-resistant, but poorly-adapted to fire.

The bottom line is:
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.

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