Two species of cyanobacteria (possibly Nostoc commune and Anabaena cylindrica)

I am an amateur naturalist trying to learn something about everything that lives in my garden.

Some of you may recall that in a recent posting I bought a puddle into my house (it was in a plastic fishtank!). Well, I've hung on to my puddle. Indeed I've been periodically topping it up with fresh puddle-water and inspecting its inhabitants under my microscope. Photos 1 and 2 show two such 'denizens of the deeps'. No, not frog or toad spawn. The scale is all wrong for that. Twenty of the larger spheres in photo 2 for example, would sit side-by-side in 1mm. In fact these are of colonies of blue-green algae (cyanobacteria).

Cyanobacteria are some of the most ancient lifeforms of all. Their microfossil record goes back 2.7 billion years. What I have learnt about them has been mostly through reading a new book - Phycology (=the study of algae) by R.E.Lee (CambridgeUni. Press) - which Santa very kindly delivered to me recently.

Like plants, cyanobacteria carry out photosynthesis. In fact, it is believed that photosynthesis evolved first in cyanobacteria and at some point in the ancient past a cell that was to become the first plant 'swallowed' (co-opted) a cyanobacterium. Chloroplasts, the green organelles responsible for photosynthesis found inside all plant cells are the remnants of these 'swallowed' cyanobacteria.

Today such photosynthetic 'slavery' still persists in the lichens. About 10% of lichens use cyanobacteria to do their photosynthesis (the other 90% use algae).

Photosynthesisis is not the only chemical magic that cyanobacteria have mastered. They are also able to 'fix' nitrogen - that is take nitrogen gas from the air and turn it into an amino acid (glutamate). No higher plants or animals can do this, and a range of plants have formed symbiotic relationships with cyanobacteria to take advantage of this ability. Some plants have special nodules on their roots to house colonies of cyanobacteria. The water fern Azolla has cavities in the leaves. According to the book above, nitrogen fixation by cyanobacteria also plays a fundamental role in keeping the world's 100million square km of paddy fields fertile in areas where otherwise farmers would be too poor to nitrogen-fertilise the soil.

The twin ability of cyanobacteria to remove nitrogen and carbon dioxide from the atmosphere had a profound affect on the earth's early climate. Over eons, cyanobacteria, as the dominant lifeform at the time, transformed an ancient atmosphere rich in CO2 and almost devoid of oxygen into the one we breathe today. A glimpse of what the ancient earth might have looked like can be seen today at Shark's Bay in Australia where warm and salty waters limit other forms of life and allow cyanobacteria to dominate and grow into large, rocky (actually calcium carbonate) colonies called stromatolites - see photo 3 which I'm using under the terms of the Wikimedia free licence. Stromatolites grow slowly and exhibit 'growth ring' like features. Analysis of these has allowed scientists to determine that for example, 1-billion years ago the earth's year comprised 435 days [1].

So, how do you set about identifying the species of a cyanobacterium? The answer is: with difficulty! Like so many areas of biology at present, DNA analysis is over-turning a lot of old species definitions. Things are further complicated by the fact that the appearance (morphology) of a specimen of a cyanobacterium can depend strongly on the conditions in which it has grown. Nevertheless with a little patience it's possible for the amateur (me!) to make a little progress. I've also been fortunate in having been able to borrow a copy of the hefty The Freshwater Algal Flora of the British Isles (Whitton and Brook). Firstly you need to know you're looking at a cyanobacterium. If the cells you're examining show any significant internal structure (especially a nucleus) then it's not a cyanobacterium, and is instead a true algae. Next one needs to take careful note of the detailed shape of the colony. For example, if your cyanobacteria exhibit chain-like growth its important to note whether the filaments branch, whether or not they taper towards the ends and whether or not the cells are encased in any sort of slimy envelope (as they are in photo 2). These features help separate the main genuses. Finally, it's important to note the presence and form of any heterocysts and akinetes. I've labelled these in photo 4. Heterocysts are specialised, largely colourless cells that carry out nitrogen fixation. My impression from the textbooks is that the role of akinetes is a bit of mystery. They have reduced photosynthetic ability and seem to be involved in food storage. Anyway based on these features and Whitton and Brook's book above I'm tentatively identifying my cyanobacteria as Anabaena cylindrica and Nostoc commune. As always I'm happy for anyone out there to correct me.

Finally, one of the most amazing things I learnt about cyanobacteria is the way in which some of them achieve movement. Some species develop tiny gas bubbles (vacuoles) inside the cells that help them float upwards in water to receive more sunlight. More fantastically some species can undertake a form of movement known as gliding. Here the surface of the cells is sculptured in a series of grooves. The grooves may spiral around along a chain of cells. The cell pumps slime into the grooves through tiny pores. If a chain of cells is close to a surface, the flow of slime pushes against the surface and causes the whole filament to glide along over the surface at up to half a mm per second. Hooray for slime power!

Reference
[1] J.P. VANYO, S.M. AWRAMIK Precambrian Research, 29 ( 1985 ) 121-142, STROMATOLITES AND EARTH-SUN-MOON DYNAMICS,

A fungus gnat , Sciarida (possibly Bradysia)

I am an amateur naturalist trying to learn something about everything living in my garden.

Buoyed up by my successful (?!) identification of a fly to species level in my previous posting, today I'm taking on a related, though tougher challenge: the little gnat in photo 1 (click on photo's to enlarge). This one was around in my garden mid-May last.

As I've discovered through writing this blog, to stand any real chance of identifying the smaller insects it's pretty much essential to have a microscope. This needn't cost the earth. Photo 1 was taken by holding a 'point and click' digital camera up to the eyepiece of a sub-£100 'DM2' stereo microscope. With 10x and 20x eyepieces this would probably suffice for a fair range of the needs of many amatuer naturalists though if you want to study the more minute structures such as mushroom spores, or the smaller pondlife, a microscope capable of 1000x magnification is needed. I have a (sub-£200) Westbury SP2 microscope which I've found to be thoroughly adequate for all my needs (the only minor drawback, for those in-the-know about such things, is I'm not certain this particular scope has the option to be equipped for 'dark field' operation, though this is a 'luxury' rather than a 'staple'). For anyone considering making a purchase, I have always been very satisfied with the service from Brunel Microscopes Ltd (I am unconnected with the company, and have received no payments for plugging them here!).

To set about identifying my fly I turned first to "A Key to the families of British Diptera" by D.M.. Unwin, available free here. This is designed specifically with the amateur in mind, being copiously illustrated to explain any technical terms. There are more than 80 families of British fly. The fact that my fly has long, thread-like, multi-segmented antennae immediately rules out more than 5o of these however, and places my fly in the nematocera, a sub-order of around 30 families. To distinguish between these its necessary, in part, to carefully examine your fly's wing. In my last posting on a crane fly I discussed the prehistoric origins of fly wings and the so-called 'Comstock-Needham' code for labelling up their veins. I'll not repeat this here and simply point out that I've labelled up the wing veins in photo 1.

With the wings of my fly in view, the key above pretty quickly bought me to a choice of my gnat being in one of two families: the Sciaridae or the Mycetophilidae. The 'decider' was the eyes. Photo 2 (taken from above looking directly down onto the antennae) shows my fly's 'left' and 'right' eyes, though this is a rather arbitrary choice of words since in fact the eyes are joined together to form one continuous band above the antennae. If ever you wanted an example of how 'alien' is the world of insects' senses, surely having eyes that join on top of you're head is one! Anyway, this 'eye bridge' decides against my fly being in the Mycetophildae and makes it a member of the Sciaridae. In searching for information on sciarid flies I came across two useful websites, the first dedicated to Sciariod flies, and the second, a list of free, online keys to different diptera.

The Sciarid flies are sometimes called 'fungus gnats', mushrooms being the larval food for some species. Mushrooms are not the only food however, and species have been reported emerging from a wide variety of substances from dead animals to birds' nests. Perhaps the most amazing thing I learnt about Sciarids in a short time searching is that the larvae of some occasionally undergo mass movements, thousands of them marching in columns several centimetres wide and metres long. I found an online paper reporting one such movement here [1]. It seems no one knows why they do this.

So far so good! Unfortunately, whilst identifying a fly to family level (Sciaridae in this case) is generally tractable, getting much further can be decidedly tricky. The first problem is that there are a lot of families of fly and finding a text-book or key that deals with yours can be difficult or indeed impossible. As luck would have it however, having become interested in flies and having something of a passion for natural history books, last summer I treated myself to some of the Handbooks for the Identification of British Insects from the Royal Entomological Society, amongst them Sciarid Flies by P. Freeman.

The book starts a little ominously:

[Sciard] taxonomy has always presented problems [...] the student has always been faced with a mass of similar looking species which he has been unable to group adequately.

Fortunately Freeman's book provides a detailed guide to identification, covering about half (according to this paper [2], as of 2005 there were 263 species of British Sciaridae in total) the British species across 18 genera.

So how did I get on sifting through the 18 genera of Sciaridae in Dr. Freeman's key? Well, On the basis of wing-vein shape and length, I was able to rule out 4 of the 18 genera; There was no sign of largish hairs ('macrotrichia') on my fly's wing veins, though there were tiny, downy hairs ( 'microtrichia'). This rules out another 5 genera; My fly has tiny spurs on its leg tibia (see photo 1). These are not 'distrinctly longer than the width of the tibia', ruling out the genus Corynoptera. After a little further work I was down to a choice between the genus Bradysia and the genus Lycoriella...and...I dropped my fly on the floor and lost it!!! On the basis of a couple of half-examined features, and the fact that Bradysia is the larger, more common genus, I'm going for Bradysia. But it all goes to show - you can't win 'em all!

Reference
[1] C. T. Brues, A Migrating Army of Sciarid Larvae in the Philippines, Psyche 58:73-76, 1951.

[2] Zoological Journal of the Linnean Society, 2006,146, 1–147. The sciarid fauna of the British Isles (Diptera: Sciaridae), including descriptions of six new species Frank Menzel, Jane E. Smith and Peter J. Chandler

A crane fly Limonia nebeculosa

I am an amateur naturalist trying to learn something about everything living in my garden.

My garden, along with the rest of the UK, is currently buried beneath a thick blanket of snow. Aside from a collection of tits on my bird feeder there's little sign of life. For this posting therefore, I'm falling back to a photo of a crane fly I took in summer (photo 1. Click on photo's to enlarge). Dozens of them swarmed out from amongst some garden ivy I happened to disturb at the time.

I know almost nothing about flies (diptera). Along with beetles, ichneumon wasps and various other orders of insect however, they strike me as offering rather "good value" to any amateur naturalist keen to make a genuine contribution to science since a) there are very large numbers of them (15,000 species of fly in Europe alone) b) they can display a rich and complex behaviour (see my posting on P. nobilitatus for example) and c) for countless species almost nothing is known. Take hoverflies for example. After hundreds of years of intense study by armies of naturalists there can be few countries in the world whose natural history has been so well catalogued as Britain's. Further, there are few flies as conspicuous as hoverflies. Yet even for these, a staggering 40% of the larvae of the 265 British hoverfly species of are simply unknown. In the U.S. its 93%. (This, at least, was the situation persisting in 1993 when my copy of 'Colour Guide to Hoverfly Larvae' (G.E.Rotheray) was published). Anyway, we're not here to discuss hoverflies. On to the star of today's show...

What makes a crane fly a crane fly? Well, firstly flies (=the order diptera) are separated from other insects by the presence of two vestigial wings called halteres. I've ringed these in photo 2. Next, the order diptera is separated into two sub-orders of flies called the nematocera and the brachycera. The split is based on the structure of the antennae - the nematocera all have long, thread-like antennae with more than five segments. You can see this in photo 3. The sub-order nematocera gets further subdivided into more than 70 families of fly, the crane flies amongst them. If you want a fuller flavour of how these families are separated, the redoubtable Field Studies Council has made a key to the families of fly by D.M. Unwin freely available here.

It used to be that all crane flies were clumped together in one family called the Tipulidae. At some point however it was decided to split this family into four, the Tipulidae, Pediciidae, Limoniidae and the Cylindrotomidae. I read on the (searchable) Catalog of the Craneflies of the World that worldwide there are more than 10,000 species of Limoniidae, 4000 Tipulidae nearly 500 Pediciidea and 70-odd Cylindrotomidae. Separating these families is a tricky job. To complicate matters further, recent DNA studies [2] are casting doubt on the very existence of the Limoniidae as a family.

The whole thing is rather confusing for the amateur (=me!) and for a long time whilst preparing this posting I despaired of being able to identify my crane fly. Fortunately, rescue was at hand in the form of an excellent set of test keys from Alan Stubbs I found on the Dipterists Forum website.

Before discussing these keys I need say something about how dipterists characterise the wings of flies: An influential theory, originally due to Comstock and Needham in the 1890's, is that way back in prehistory, a first primeval insect wing evolved. Exactly how this first wing appeared is still uncertain but a current theory [1] is that it evolved from the multi-branched external gills seen on the larvae of some aquatic insects such as mayflies. The veins in insect wings are hypothesised to be modifications of these gill 'tubes' (trachea). Anyway, assuming the existence of this ancestral wing, Comstock and Needham named the veins in it the Costa (C), the Radius (R), the Media (M), the Cubitus (Cu) and the Anal veins (A). As these veins fanned out through the ancestral wing they forked. So, for example, the radius vein, R, is supposed to have forked into five sub-veins called (logically enough) R1 to R5. No modern fly has retained all the veins of the ancestral wing, over millenia evolution has caused different families of fly to lose different veins. Which veins a fly has retained however is a very important clue to its identification.

Photo 4 shows the wing of my crane fly labelled up with the help of Alan Stubbs' keys above according to the Comstock Needham system.

There was one more piece of information I needed, namely whether my crane fly's palps (=little facial apendages) were long or short. Photo 5 shows they're short.

Armed with this information I was finally able to identify my cranefly as Limonia nebeculosa. Final 'clinchers' were the presence of 3-coloured bands on my fly's femurs (enlarge to see these in photo 1) and the sort of smudgy 'hoop' on the wing I've delineated with the dashed white line in photo 4.

Today's posting was a bit technical in places but I am pleased to have identified my first fly to species level. Only another 250,000 to go!

References

[1] Averof M., Cohen S.M., Nature 385, 627-630, 1997 Evolutionary origin of insect wings from ancestral gills.

[2] Matthew J., et.al. Phylogenetic synthesis of morphological and molecular data reveals new insights into the higher-level classification of Tipuloidea (Diptera), Systematic Entomology (2010), DOI: 10.1111/j.1365-3113.2010.00524.x

A lichen Malanelia subaurifera

I am an amatuer naturalist trying to learn something about everything living in my garden.

Photo 1 shows a lichen growing, amongst a number of similar patches, on a wooden bird table in my garden.

I am very far from being an expert on lichen identification but in the course of doing this blog over several years I have picked up a few tricks. One is to examine your lichen through a hand lens for any characteristic surface lumps on bumps. Some lichen species become decorated with powdery granules called soralia. Others with tiny sausage shaped protuberances called isidia. For my lichen, the latter are present in abundance as can be seen in the close-up Photo 2 (click on photos to enlarge).

Another trick to help with lichen identification is to check the under surface. In photo 2 I have peeled back a small section to reveal a black underside with a covering of tiny, root-like hairs. In the jargon, these are known as rhizines. Not all lichens have them. They are not roots in the traditional sense, since they do not function to suck-up water as do the roots of plants. Rather their job seems to be to help anchor lichens to surfaces.

Armed with the features above and my trusty copy of Lichens (Dobson, Richmond Publishing) I'm confident to identify my lichen as Melanelia (Parmelia) subaurifera. The book suggests a final test: gently rubbing the surface should leave a pale yellow-white abrasion. Photo 4 shows this.

I am fond of lichens and so was very pleased when someone recently made me a present of the new edition of Lichen Biology (Ed. Thomas H Nash III, publ. Cambridge). This book is primarily aimed at professionals and I don't pretend to have followed some of the very detailed sections on e.g. lichen biochemistry, but I was able to follow others and came away with a new respect for the intricacy with which nature adapts these little creatures to their environment. Take for example the construction of the little air-filled spaces often found inside the bodies of lichens:

Under a microscope a lichen is revealed to be a mass of long, spaghetti-like fungal cells ('hyphae'), mixed-through with a sprinkling of green, single-celled algae or sometimes cyanobacteria. (The fungus carries out various tasks such as water storage. The algae or cyanbacteria do what no fungus can: photosynthesise food from sunlight). In considering this description however it would be wrong to picture things as a random tangle of fungal threads and algal cells. Photo 5 shows a lichen cross section I made and discussed some time ago (here) and reveals that things are far from random. Of particular relevance for today's posting is the layer known as the medulla that contains a lot of air-filled voids (see the region of the box in photo 5 for example). What is the purpose of these voids? The answer of course is that algae, like all plants, 'feed' (via photosynthesis) on a diet of sunlight and gaseous carbon dioxide. This is the key to understanding the voids: they are present to allow the flow of gaseous CO2 gas to the algae.

So far so good, but possibly it might occur to you to wonder what happens when it rains?! Do these voids fill up with water and in so-doing stifle CO2 flow, and hence photosynthesis, in the lichen? As I learnt from the book above Nature, of course, has an answer. In one chapter, a remarkable photograph taken by Rosmarie Honeggar with an electron microscope reveals how the fungal threads in the medulla carefully coat themselves and their precious cargo of algal cells in a minuscule layer of water-repellent proteins. This remarkable water repellent 'jacket' prevents the medulla from becoming saturated with water and so maintains the algae in a gaseous environment conducive to photosynthesis.

The water-repelling proteins the fungal hyphae secrete are known as hydrophobins and their discussion would make a lengthy posting in its own right. They were unknown to science until the 1990's when they were discovered by Wessel and co-workers in a fungus called Schizophyllum commune. Since their discovery these remarkable molecules have turned out to be widespread amongst fungi, with fungi using them in a variety of ingenious ways to 'manipulate' the surface tension of watery environments. For example, in order to help their spores get airborne, some plant-infecting fungi coat their spores in hydrophobins so as to prevent them becoming trapped or stuck together by thin films of water. Hydrophobins also help the infectious spores stick to the waxy, water-repellent leaves of targeted host plants. You can find a short introduction and further references on hydrophobins in lichens here ( P.S. Dyer, New Phytologist (2002) 154 : 1–4).

So there you have it! Minuscule, air-filled voids in a wafer-thin lichen...but take a closer look and as so often in natural history, one finds a hitherto unimagined world of subtlety and sophistication.

Greater Plantain Plantago major

I am an amateur naturalist trying to learn something about everything living in my garden.

Taken in August, photo 1 shows a specimen of the weed Greater Plantain (Plantago major) growing on my lawn. This plant is very common in the UK and likely to be encountered on any patch of rough wasteland (= my lawn!).

For such a common plant I have found relatively few freely available papers dealing with Greater Plantain on the web. There are a number (such as here and here) that deal with its medicinal properties. Plantago major appears to have a long list of antibacterial, antifungal and antitumeral properties and has even been recommended to treat the bites of rapid dogs! Amongst the interesting snippets I picked up from skimming the paper by Velaso-Lezama et.al. [1] is that Greater Plantain is today used as a medicinal tonic in Mexico having been originally introduced there by the Spanish conquistadors.

A number of species of Plantain grow in the UK including Ribwort- and Buck's Horn- , both of which have narrower ('lanceolate') leaves than Greater Plantain. Also Hoary Plantain (Plantago media) which as the name implies differs from Greater Plantain in having greyish down on the leaves. That at least is how things are set out in my copy of The Wild Flower Key (F. Rose, publ. Warne). If however, the Plantago media above is one and the same as the Plantago intermedia described in this paper [2] by El-Bakatoucshi et.al., then these authors cast doubt on whether major and intermedia are sufficiently distinct to be regarded as separate (sub) species.

In skimming the paper above by El-Bakatoucshi et.al. , a word I came across that was new for me was protogynous (in context: "Plantago major is protogynous"). A little research and I now understand what this means. I'll share it here for interested readers: Firstly one has to recall that for many plants, the flower is typically neither male nor female. Rather the same flower combines male pollen producing parts (the anthers) and a female reproductive part (the stigma). This gives plants an issue of how to avoid self-fertilisation (i.e. self pollination). Plants have come up with a variety of solutions including i) Ignore the problem (= allow self pollination) ii) Separate your line into two, so that some plants carry only male and others only female parts (these are the so-called dioescious plants - from the Greek "two houses" . Our old friend the stinging nettle is an example) iii) Develop some "chemical / structural" approach that avoids self pollination. I wrote about a classic example when I discussed the two types of primrose, 'pin' and 'thrum' iv) Separate the time at which the male and female parts of a flower are active / receptive. This latter method ('iv') is protogyny and is the technique adopted by Greater Plantain. The female stigmas of Greater Plantain flower are protruded 1-3 days before pollen is produced and in this way the chances of self pollination are reduced. Another of those small but elegant behaviours Mother Nature has carrying on all around us.

References
[1] Effect of Plantago major on cell proliferation in vitro R. Velasco-Lezama et.al., Journal of Ethnopharmacology 103 (2006) 36–42

[2] Introgression between Plantago major L. subspecies major and
subspecies intermedia (Gilib.) Lange. in a British population, R. El-Bakatoushi et.al. , Watsonia 26: 373-379 (2007)

Smooth Hawks-beard Crepis capillaris

I am an amateur naturalist trying to learn something about everything living in my garden.

I have mentioned previously that the pleasure for me in maintaining this blog is that some previously unnoticed (by me at least) plant or insect, once researched, takes on a whole new aspect. So it is with today's posting. A scattering of facts about the genetics of an inauspicious weed may seem obscure to some, but for me, a weed on my lawn catches my eye with a new interest these days. Photos 1,2 and 3 shows said weed. It pops up frequently in my garden.

For the unskilled amateur botanist (=me!) identifying yellow flowered weeds isn't altogether trivial as the guide books contain a long lists of yellow-flowered ragworts, fleabanes, marigolds, colts-foots, dandelions, sowthistles, cats'-ears and hawkbits. After a little work however I'm fairly confident my plant is none of these and is instead Smooth Hawks-beard (Crepis capillaris). A characteristic feature of the Hawks-beards are 'involucre bracts' (=the little leaves around the base of the flower head - best seem in photo 2) organised in distinct inner and outer rows.

Surprisingly, although it is a common UK weed, I've been able to find almost no detailed online information on Smooth Hawksbeard. One exception is the bioimages site that lists a handful of fungal rusts (including some Puccinia species - see my post here) and a gall fly known to parasitise Hawksbeard. The other exception was an online paper by Oud et.al. [1] that describes the chromosomes of C. capillaris. With my comments of the opening paragraph above in mind, its this I'll discuss.

As most people know, the DNA inside cells is packaged into structure called chromosomes. When new cells are needed by a body, the existing cells set about creating copies of themselves by dividing into two, in a process known as meitosis. (Cells destined to become specialist structures such as sperm or eggs do something slightly different called meiosis, but never mind that here). To create two cells from one its clearly necessary to replicate the DNA. To do this the chromosomes perform a complex little 'dance' inside the cell in which they double in number (in a process called interphase), pair up and line up along of the middle of the cell ('prophase' and 'metaphase' respectively) and finally split apart ('anaphase') as the cell separates into two ('telophase').

I got the hang of this terminology recently using my colouring crayons! (I've a copy of the very clever - 'The Botany Colouring Book', Young - in which you learn by doing). You can find any number of explanations on the web however (here for example).

It's perfectly possible to watch the whole miraculous 'chromosomal dance' down a hobbyists microscope. The classic place to look is at the growing tip of a young plant root where new cells are being feverishly created to grow the root. Indeed, I've tried looking for it myself a few times. I've yet to succeed in getting any really good results, but rest assured when I do there'll be a posting...

I can't resist a small digression at this point to mention microtubules. When it comes to pulling chromosomes apart (i.e. during anaphase), cells do this by strapping tiny cables (microtubules) to chromosomes in a process akin to hauling logs out a log pile by pulling on ropes. These microtubules are tiny (around 25nm across where a 'nm' is a millionanth of a millimetre) and hollow. So tiny are they that some physicists (notably the famous blackhole physicist Roger Penrose) have even speculated that inside microtubules, reality ought to be dominated by the small and weird world of quantum physics (cats being both alive-and-dead; particles being in two places at once - that sort of thing) and that signals propagating inside microtubules in the brain might have something to do with the mystery of human consciousness (you can listen to Penrose give a lecture on it here). Anyway, this is a highly contentious claim and a long way from today's discussion. To return to more certain issues:

In their paper above Oud et.al. set out to study the three-dimensional arrangement of chromosomes inside replicating cells during prophase. It turns out if you want to study chromosome arrangements inside a cell without being mired in complexity, you can do worse than make use of Smooth Hawks-beard since it has a mere 6 chromosomes (strictly one should write '2n=6' - see my previous explanation here). Compare that with humans with (2n=) 46, or some ferns with around a thousand! (I have no idea why there is such variation in nature. Generally, there is no relationship between the number of chromosomes and the complexity of an organism. Anyone?).

Trying to image the three-dimensional arrangement of tiny objects is not simple when you remember that looking down a conventional microscope all you see is a flat, two-dimensional view of an object. To achieve a 3D visualisation of chromosomes Oud et.al. used a special type of microscope known as a confocal scanning laser microscope. As anyone who has a normal microscope knows, images suffer from a limited 'depth of field': only a portion of your object appears in focus. Other parts of an object, at different depths, appear blurred. Often this is a nuisance, but confocal microscopes cleverly use it to advantage. They physically block out light from anywhere other than the one extremely thin section of a sample that happens to be in focus. The advantage of this may not be immediately clear, but the point is that by slowly varying the point of focus, one can build up a stack of images where each image contains only light coming from that single, selected slice through the sample. By taking a bunch of such images from different depths, and stacking them all together (using a computer) one arrives at a three dimensional image.

Using this method Oud et.al. arrived at the wonderful picture of the three dimensional arrangement of chromosomes in a Smooth Hawks-beard root cell in their paper. Of course, their study was not about making 'pretty pictures'. They were interested in adding to biologists' long-standing interest in knowing how chromosomes are arranged in space inside the nuclei of cells; In particular whether the arrangement is random or not. Their conclusion (as I understand it) was that although a range of differing arrangements were observed across cells, overall the chromosomes seemed to arrange themselves in space in a finite number of non-random ways.

So there we have it! A week ago, for me, an unknown weed. Now, a named plant with a intriguing inner life. Bye for now.

Footnote:
I have begun to think that my habit of normally giving only a link to articles isn't the best, as articles may disappear online in future. From now on therefore, I'm going to make an effort to selectively include proper references at the end of postings. To that end:
[1] Oud JL, Mans A, Brakenhoff GJ, van Der Voort HT, van Spronsen EA, Nanninga N. Three-dimensional chromosome arrangement of Crepis capillaris in mitotic prophase and anaphase as studied by confocal scanning laser microscopy. J Cell Sci. 1989 Mar;92:329–339

A Rotifer, Genus Mniobia

I am an amateur naturalist trying to discover everything living in my garden.

Autumn has arrived in the UK. The leaves are dropping from the trees and the wet weather has created puddles of rain water and detritus in my garden. Hoping to investigate the life therein, and having a cheap plastic fish tank to hand, rather than stand outside getting wet I decided to bring a puddle inside. It makes rather an attractive room feature don't you think?! (Photo 1).

Photo 1 shows one of the inhabitants: a rotifer.

Rotifers have long been a favorite of amateur naturalists. Under the microscope they have instant appeal. Take a drop of pondwater and you'll find smaller creatures swimming around (algae, protozoa, fungal spores...) but all tend towards the 'minimalist', typically a single, roughly spherical cell. Rotifers by comparison have a true multicellular body. The amateur gets to search for eye spots, 'buccal tubes', kidneys, ovaries... add to this the wonderful, whirling 'wheel organs' at the front of the head, setting up eddies in the water and dragging hapless prey into the mouth and onwards to the tiny but perpetually snapping jaws ('trophi'), and you have a recipe for many hours of fascinating microscope viewing. In photo 1 I didn't manage to capture the 'wheel organs'. There are some virtuosic photos by Charles Krebs here. Ultimately however there's no beating moving images, these being a fine example.

When it comes to identifying my rotifer I don't have any dedicated books. I did find a basic key in my copy of Microscopic Life in Sphagnum (Marjorie Hingley, Richmond Publishing) however. Some of the features of importance for rotifer identification include the presence of any hard shell ('lorica') and the presence of any eye spots. Mine has neither. The foot is another important feature. My rotifer crawled around 'inch worm' fashion beneath a microscope cover slip and obligingly gave me the views in photo 2. The labelled features point to my rotifer being in the genus Mniobia. As always, I'm happy to have any reader correct me.

The professionals too have given their attention to rotifers. One feature that has provoked serious study has been rotifer sexual reproduction. For many rotifer species, males are very rare. For some, no male has ever been found. How and why rotifers accomplish this, when almost everywhere else in the animal kingdom evolution has rendered reproduction reliant on two sexes, has been actively researched. I considered making this the topic for today's posting. I decided instead however to talk about some experiments into rotifer populations by a Professor Gregor Fussman and colleagues (very helpfully Prof. Fussman has made his all papers available online here).

Biologists have long been interested in trying to model the dynamics of populations. Suppose an isolated island starts out supporting a population of, say, a hundred rabbits and ten foxes. Biologists would like to be able to predict how many foxes might exist on the island a certain number of years into the future. The non-mathematically-minded amongst you (the others might want to skip this bit) might be puzzled by the meaning of the word "model" in the sentence before. Basically it means this: Take a pen and paper. In the middle of your page write an equals sign ('='). On one side of the equals-sign write a letter ('f' say) to represent the thing you're trying the predict (here, the rate at which the fox population is changing). On the other, write all the stuff you guess 'f' depends on - for instance, one might guess the size of the fox population would depend on the size of the rabbit population, the breeding rate of foxes, the old-age-limit of foxes etc. Finally, take the equation you've by now written down, and stuff it into a computer (i.e. tell the computer to plot a graph of the fox population over time using your equation). Of course there are many subtleties and details in order to do this sort of thing well, but in principal at least that is how population models are done.

Rather than 'foxes', Fussman and colleagues set out to model a population of rotifers (Brachionus calyciflorus). The rotifers were feeding on algae ('the rabbits') called Chlorella vulgaris not unlike the alga I blogged here. Rather than an 'isolated island', the environment was a 'chemostat' which is basically a fancy fishtank with tubes in and out in order to controllably input and extract nutrients for the algae to feed on ('grass for the rabbits'). Fussan and team wrote down a set of equations they presumed took account of all the factors that would influence the population growth of their rotifers and fed their euqation into a computer. When the computer results were compared with real life however, they got a surprise: The predictions of their model were in gross disagreement with experiment.

In a textbook example of the scientific method the investigators set out to track down the 'missing ingredient' from their equations. The answer, when it was found, was sufficiently surprising and profound to ensure its publication in the prestigious journal 'Nature'.

The hidden factor influencing their population experiments could be summed up in a word: Evolution. This was a great surprise. After all, the effects of evolution are only 'supposed' to show themselves only over millenia. Evolution doesn't go around dominating the behaviour of fishtanks over a period of a fortnight, right!? What was going on? The answer was subtle: It turned out that the algae in the chemostat occurred in two subtly different forms - the species existed as two clones (I'll call them 'A' and 'B' here). Although only a little different, it transpired that rotifers were unable to 'go forth and multiply' when feeding on one of the clones, 'A', but could happily do so when feeding on the other ('B'). When a population of predatory rotifers was introduced to a population of algae, at first there would be plenty of both types of clone. The hungry rotifers would start to feed on the B's and the rotifer population would grow. Simulataneously, the population of 'A' algae would also grow as they carried on reproducing, free from predation. By contrast, alga B's population would fall, not only because they were being eaten up by rotifers, but also because the bugeoning population of 'inedible' A's was using up an inreasing amount of the tank's nutriants. Eventually the population of 'B' could crash to zero...

...And there it was: Darwin's famous "survival of the fittest" acting on a small difference between two sub-species so as to drive one to extinction in mere weeks!

Actually, my explanation above is oversimplified. In fact the B's didn't always disappear. Sometimes, it was the rotifers whose population would crash as they ran short of food as the B-algae became scarce. The disappearance of predators would then give the 'B' algae the chance to recover. Rather than complete extinctions, the experimenters often observed more complicated oscillations in population sizes in their tank therefore. Nevertheless, once suitably analysed, the conclusion was the same: Evolution was a powerful force at work in their system.

The implications of this discovery for biologists seeking to model important systems may be very large. If evolution is a driving force for the dynamics of algae in a fishtank on short timescales, is it also an important, fast-acting player in such vast and critical eco-systems as the oceans' plankton food chains?

I don't know the status of this last suggestion. I do know however that these days a humble puddle in my back garden evokes a new fascination. Hoorah for natural history!

A lichenicolous fungus Illosporiopsis (syn. Hobsonia) christiansenii

I am an amateur naturalist trying to learn something about everything living in my garden.

No, not another lichen posting! Instead, the star of today's posting - the pink blobs in photo 1 - is a fungus. Specifically a lichenicolous fungus (from the Latin colous = living amongst [lichen]).

The lichen being infested here is our old friend Physcia tenella.

Photo 2 shows the rather lumpy, 'coralloid' texture of the fungal blobs close up.

I first noticed pink blobs of this type some years ago on a country walk. I struggled to identify them for a long time but an acquaintance suggested the fungus Marchandiomyces. Searching the internet for more information led me to the very nice website of Alan Silverside. There I found pictures of two species: the rich-pink blobs of M. corallinus and the orangey-pink blobs of M. aurantiacus. I was ready to settle for one of these, but then I noticed a comment alluding to yet another pink-blob species called Illosporiopsis christianesnii. (There is yet another called Hobsonia christiansenii - but as far as I can tell this and Illosporiopsis are the same).

Distinguishing between these various blobs seemed a forlorn hope. As it said in a paper by Sikaroodi et.al. (Mycological Reserach, April 2001) I came across during my searches

"These [species] are frequently misidentified because of a paucity of morphological characters"

I was about to quit, but then I caught sight (here and in a paper by Lowen et.al. Mycologica 78(5), p.842) of a mention that the 'conidia' (= asexual spores) of I. christiansenii had a characteristic 'spiral' appearance. I took a tiny part of my fungus in a drop of water, squashed it between a slide and cover slip and viewed it with my trusty student microscope. The result is shown in photo 3 (click to enlarge).

I'm not expert enough to be confident of what I'm really looking at here. Furthermore, working at x1000 magnification is a tricky and frustrating business - there's hardly any depth of focus and the slightest knock sends things scudding out of the field of view. Nevertheless I was left pretty confident there were indeed some spiral 'objects' in my sample (the object in the photo inset for example, and another in the main image above the number '3'). On that basis I'm identifying my fungus as Illosporiopsis (syn. Hobsonia) christiansenii.

Searching more generally for information about lichenicolous fungi I was rewarded by finding the splendid review article by Lawry and Diederich here. From this I learn that the whole research topic of lichenicolous fungi is enjoying a purple (pink?!) patch. From a single illustrated species (a gall on the lichen 'Usnea') in 1792, the number of known species grew steadily to reach around 686 in 1989. Over the past 10-years however, as scientists around the world have started look in earnest for such lichen-loving fungi, the number of known species has more than doubled.

With this explosion in species-count is coming a growing appreciation of just how rich a field-of-enquiry the lichenicolous fungi represent. Take the task of unravelling and understanding the interactions between the attacking fungus and its target lichen. Some fungi are very unfussy, being adaptable to a wide range of lichens. Others have a very intimate and specific relationship with only one or two hosts. Some invaders aggressively attack and kill their target lichen. Others are parasitic, insinuating their hyphae (=the long tube-like cells that make up a fungus) into the cells of their host to suck the juices, vampire-like, from their cells. Some lichenicolous fungi even stage a 'take-over' bid: A lichen is basically a fungus that is 'farming' a crop of algae (see my post here). The game plan of some lichenicolous fungi is to kill the 'farmer'-fungus' in order to acquire his algae.

There are more questions over how lichenicolous propogate and spread themselves. It's hypothesised that some may hitch a lift with roving, lichen-feeding mites. But generally not much seems to be known. There are unanswered questions about the sensitivity of lichenicolous fungi to air quality. Certainly some lichens are incredibly sensitive to impure air, unable to survive even trace amounts of pollution. Whether this holds for their attackers isn't known.

There are further questions about how lichenicolous fungi affect the ecology of a region. It's been argued by biologists that having a lot of parasites in some eco-system ought to encourage a lot of species diversity. Whether this is born out in regions where parasitic lichenicolous fungi are prevalent however is not well studied however.

These topics (and a lot more) are discussed in the review above. All in all, I suspect that any amateur naturalist hoping to make some genuine and lasting contribution to scientific understanding could do worse than to cultivate an interest in lichenicolous fungi!

To return to the pink blob species M. corallinus and I. christiansenii, and the paper I mentioned above by Sikaroodi et.al., a remarkable thing to learn was that these two nominally identical blobby fungi in fact represent two entirely separate fungal kingdoms. There are millions of species of fungi, but (crudely) they can be split into two huge groups. There is a huge group of fungi that grow their spores inside little sausage-shaped bags called asci (see photo 4 on my posting here). Such fungi are termed ascomycetes. The other group grow their spores, not inside asci, but on the ends of sausage-shaped protruberences called basdia. Such fungi are termed basidiomycetes. From everything I've read this is a very deep and ancient division, the ascomycota and basidiomycota representing an ancient 'parting on the ways' in the evolution of fungi. What's surprises me therefore, is that whilst M. corallinus and I. christiansenii seem almost indentical in every regard (both are small pink blobs, and both grow on the same types of lichens), whilst the former is a basidiomycete the latter is an ascomycete. Now, sometimes, entirely different lifeforms can end up evolving very similar bodies simply because these are the best bodies for the life they're trying to live ('convergent evolution'): Think 'whales' and 'fishes' or 'birds' and 'bats'. Have two very distant fungal cousins independently evolved the conclusion that if you want to survive on lichen, being a small pink blob is a good way to go? The plot only thickens when you learn that although DNA testing shows the species above to be members of the basidiomycota and ascomycota respectively (and therefore that they should grow their (sexual) spores in quite different ways) in fact for neither species has this (sexual) fruiting stage ever actually been seen! (Though it should be remarked that the same was true of the blob M. aurantiacus until recently when a fruit body ('teleomorph') was discovered by Diederich and co workers).

So there we have it. A tiny inconspicuous fungus occupying the (to our human eyes) minute and obscure niche of subsisting in the crevices of a lichen. And yet what a rich and unexplored natural history awaits.

"Great fleas have little fleas upon their backs to bite 'em,
And little fleas have lesser fleas, and so ad infinitum"
( Augustus de Morgan, 1806-1871)

Meadow Brown Maniola jurtina

I am an amateur naturalist trying to identify and learn something about, everything living in my garden.

At the risk of butterfly-blog-overload ("Impossible!" I hear you cry) photo 1 follows on from my last posting and shows a Meadow Brown (Maniola jurtina). The photo was taken late last summer.

The Meadow Brown is fairly easy to identify, though it is worth checking you are not looking at a Gatekeeper (see my posting here) or Ringlet (some photos here).

My specimen here is tattered and faded - not uncommon for the Meadow Brown in late summer. Earlier in the season the upper parts of the wings would have been warm orange.

As with my Red Admiral last time, most of what I've learnt about my butterfly is taken from the splendid new book The Butterflies of Britain and Ireland (Jeremy Thomas and Richard Lewington, British Wildlife Publishing). Unlike many guidebooks, which merely supply you the name and a few scant details (foodstuff etc.) for your specimen, this book sets out to survey the literature and provide a scholarly essay on the natural history of each butterfly individually (not unlike what I aspire to do on my blog, though I don't for a moment pretend to the same levels of completeness or professionalism).

The Meadow Brown turns out to have a particularly rich history of scientific study. In particular it was extensively studied in the 1950's by the famous lepidopterist E.B. Ford and co-workers who were attempting to bring a new, quantitative understanding to genetics and evolution. Butterflies and moths make very good subjects if you want to study evolution: Their lives are relatively short thereby permitting one to follow some feature of interest across multiple generations. And at the same time, variations in their colourful wing patterns give you a very obvious and visible 'signature' that you can set about trying to relate to their genetic makeup.

Ford and others were interested in a wide variation that occurs in the number and spacing of some black spots that appear on the underwings of Meadow Browns. Unfortunately my Meadow Brown wouldn't stay still long enough for me to get a non-blurred photo of these but you can just about make out some spots towards the bottom of the wings in photo 2 (click to enlarge).

At this point I can't resist a small digression to talk about about E.B. Ford. A professor at Oxford University, by many accounts Ford seems to have been a somewhat 'difficult' character. He seems to have been not at all fond of women. He campaigned strongly against their being accepted to the then, all-male, college of All Souls. I also recall hearing somewhere he once refused to give a lecture on the basis that only females had turned up and that therefore there was no one 'worthy' to receive it! (I should add that I have failed to find a reference on the web to back-up this second story. I hope I am not falsely maligning Prof. Ford by it. If someone tells me it's incorrect I'll certainly take it down).

I have not found any free online archive of Ford's papers (anyone?). Whilst searching however, I did find an excellent and comprehensive archive of the papers of Ford's long-time co-worker R.A. Fisher here. (The good people of the University of Adelaide seem to be suffering from the strange delusion - shared by too few UK universities and institutions- that having presumably paid for some piece of university research in the first place, tax payers should get the chance to read the results without having to pay a second time to some private journal publishing house for the privilege!)

Anyway, getting back to the Meadow Brown. Through their work, Ford and others discovered some intriguing and puzzling trends in the wing-spot variation of this insect. They discovered, for example, that the typical spot pattern of Meadow Browns on small islands differed from that on larger islands. The question (unanswered at the time) was why?! What were the evolutionary causes and benefits driving this variation?

As the book above explains, answers only really emerged much later. The studies by Paul Brakefield were particularly important (you can find one of his papers here). It has become clear that spot variation is linked to habitat, in particular the extent of the ground-cover available in some region. Butterflies living in an area with lots of ground cover (long grass) can spend a lot of their time hidden away. For these butterflies, lots of spots would be a positive hindrance - if anything likely to 'blow their cover' to predators. Butterflies from areas with lots of long grass tend to lack lots of small spots therefore. They retain the big 'eye spots' seen in photos 1 and 2, but when resting in deep grass keep these hidden away behind their lower wings, bringing them out only as a 'startle measure' to frighten predators if they are attacked (I spoke more about eyespots here).

On the other hand, butterflies living in areas of sparse, grazed, or stunted vegetation (a small, wind-swept island as in Ford and others' study above for example) are forced to spend much of their time 'out in the open'. Such butterflies tend to have a lot of small wing spots. The reason is that these act as an 'always on' predator defence; An attacking bird is drawn to peck at the black spots on the 'expendable' wing tips, reducing the chance that the insect's precious head or body will suffer the first attack and thereby giving the butterfly the chance to escape attack with only minor damage.

There is much more than could said, especially about some further differences between male and female Meadow Browns. The former need to spend more time 'on the wing' and hence benefiting from some further differences in spot pattern. Since the authors above have already done it so much better than I might howver, I'll stop here, refer you to their book, and, apropos of nothing, end with a quote from the great P.G. Wodehouse:

The least thing upset him on the links. He missed short putts because of the uproar of butterflies in the adjoining meadows.

Red Admiral Butterfly Vanessa atalanta

I am an amateur naturalist trying to learn something about everything living in my garden.

Taken last summer, photo 1 shows a butterfly basking in the sun on my garden table. There's no mistaking it as a Red Admiral (Vanessa atalanta).

What I have learnt about Red Admirals I have got from reading my newly acquired copy of The Butterflies of Britain and Ireland (Thomas and Lewington, publ. British Wildlife Publishing). This is a major new work that I can't recommend too highly for the interested amateur. All 72 'properly recognised' species of UK butterfly, each copiously and beautifully illustrated as egg, adult, caterpillar and chrysalis, and each with a full and scholarly essay on its natural history.

In common with the Painted Lady I blogged here, the Red Admiral undergoes a remarkable migration. Red Admirals overwinter in Southern Europe, not as adults, but as caterpillars, maturing slowly in the cool Southern winters. In early spring the (by then) adult Admirals start to fly North. Some will fly as far as Scandinavia.

When they arrive at a suitably Northern destination, the males set up territories on high ground where they mate with females which go on to lay their eggs, singly, on plants such as nettle (see my posting here). Eggs hatch after about a week and the emerged caterpillers mature over about a four week period. The caterpillars carry a dozen or so sets of bristles along their bodies and come in two forms: black and green. They have the evolved the remarkable trick of constructing a 'tent' of leaves, sewn together with silk (there's a picture here). Sitting inside they can munch away out the sight of predators. The caterpillars pupate in an attractive grey and yellow-spotted chrysalis to emerge to later as the beautiful butterfly of photo 1. Around October, as the weather cools, these adults fly to back to Southern Europe and the cycle begins again.

The book above mentions a fascinating puzzle for a population of Scandinavian Red Admirals. Leaving Scandinavia at the end of summer the adults start out by flying due South. After a time however, they reach the coast in Southern Sweden. At this point the butterflies 'cleverly' turn West in order to minimise the distance they need to fly across open sea before reaching land again at Denmark. From Sweden, the coast of Denmark is 24km away and only barely visible to human eyes in a fine day. How the butterflies are able to detect it and know to turn West therefore is a puzzle. It is speculated that they may be making use of an ability of many insects have to see the 'polarisation state' of light. 'Polarisation' is a property of beams of light that humans can't see, but suffice to say land and water can affect it in different ways. It is theorised the migrating Scandinavian Red Admirals are using this to aid them in detecting land at a distance. This appears to be unproven however. Another of nature's mysteries!

A lichen: Lecidella elaeochroma

I am an amateur naturalist trying to discover everything that lives in my garden.

Once upon a time there was a large, upright apple tree in my garden. And then quite suddenly, one night, there wasn't!

What happened is a story most relevant for this blog...but one for another time. For today let me remark only that this calamity gave me an unprecedented opportunity to inspect my tree's upper branches for one of my favourite lifeforms - the lichens.

Photo 1 shows a lichen new for this blog (the grey smudge that is, the yellow is Xanthoria parientina I've blogged previously). Photo 2 shows a closeup of my lichen's areolate thallus (=cracked surface) and black, lecideine apothecia (= fruit bodies - see my artwork and explanation here).

Despite my fondness for lichens I am very far from being an expert. One problem facing the amateur is that many species look rather similar to the eye. Some are all but impossible to separate by anyone who does not happen to possess a forensic chemistry laboratory. (This is not a joke. It is not uncommon for the professionals to turn to e.g. chemical chromatography in pursuit of accurate identifications of lichens).

Fortunately there are a few 'tricks' available to the amateur. One is to observe your lichen under UV light. This is not as difficult as it sounds. In my case a battery-powered banknote reader from a 'pound store' (that's 'dollar shop', '100yen shop'... to those of you reading overseas) yielded the rather lovely result at the bottom of photo 2. The point is that had my lichen been the superficially similar Fuscidea cyathoides (picture available here), also occasionally found on wood, then UV light wouldn't produce the glow seen here. In the jargon, F. cyathoides is 'UV-' . By comparison, as I learnt from to my copy of Lichens (Dobson, Richmond Publ.) the common UK lichen Lecidella elaeochroma is 'UV+ orange' - clearly a good fit and my identification for today (as always I'm happy to be corrected).

I have mentioned previously a question that I have puzzled over regarding lichen: My (decidedly amateur) understanding of evolution has always been that, over time, it drives species towards adopting the optimal form for surviving in their environment. What has puzzled me is how then, it can be commonplace to see lichens with really quite dissimilar features occupying the same environmental niche. Inspect a few twigs on a tree and it's really not uncommon to find, side-by-side, both crustose (pancake-like) lichens, and, as here say, the bright yellow, foliose (=leafy) lichen X. parientina. To survive on wood, how can it be 'evolutionarily optimal' to be a bunch of bright yellow flakes, and optimal to be a grey pancake. Surely one ought to have 'won the argument'? It was satisfying recently therefore to come across a section in the book Introduction to Bryophytes (Vanderpooten and Goffinet, publ. Cambridge) that I think has given me the inkling of a solution to my confusion.

The book describes how some species of moss have become expert in seizing the opportuntity to colonise fleeting, virgin, environments. A newly appeared patch of burnt ground after a forest fire for example. Clearly being 'first moss on the scene' has the benefit you will enjoy the resources of your new home free from the pressure of competition. There is a price to pay for such a lifestyle however. To succeed at rapidly detecting newly emerged environments requires that you to put a great deal of your energies into sending out countless 'scouts' (a.k.a. spores) to explore your environs. By definition, if you're putting your energies into volume spore production, you are precisely not putting them into your own growth (producing lots of leaves etc.). Such 'fugitive mosses' therefore tend to be slight, quick-to-mature, normally annual plants, producing large numbers of small 20um spores.

Now 'fugitive' is not the only survival strategy amongst mosses. Enter the dominants. Dominants aim to out-compete other mosses for light and nutriants by growing faster and larger. This is a perfectly reasonable strategy, but again has its limitations. By investing a large proportion of their energy into the rapid growth of leaves etc. such mosses are left with little energy for the production of spores. Dominants then, will be less successful at rapidily discovering new areas, and tend to be larger, perennenial mosses with fewer spores. This is far from the complete story. As well as doimants and fugitives, the book above goes on to discuss the strategy of 'colonists', 'perennial stayers' and 'annual shuttles'. I have not found any freely available articles discussing similar issues for lichen (anyone?), but I think its not unreasoanble to suppose some similar ecology might hold for these fellow tree- and rock-dwellers.

All of which brings me back to my puzzle of how evolution can have a arrived at two such different forms (body shapes and colours) as optimal solutions for lichens living in the same place (a twig). I don't pretend a complete answer, but I feel I may have started to get an inkling of understanding. I think my confusion likely stems from woolly thinking on my part, namley, in erroniously imagining that evolution is about optimising a creature's form to fit a place. The more I've thought about the moss examples above however, the clearer it seems to me now that it is not 'body shape' that evolution is working to optimise, but rather the whole organism. That is, not merely its shape and colour, but rather the totality of its life cycle and survival strategy. Furthermore it is not sufficient to think of a lichen's 'environment' as being merely some unchanging point in space (the surface of a twig, say). This misses the very significant additional fact that our twig is subject to an annual cycle of dramatically changing seasons and that it itself is a growing, changing, transitory thing. At the risk of sounding too poetical, thinking of the lichens on my tree now I begin to get an image of a complex spaghetti of life histories and strategies at work. It is facile to try to ask whether 'yellow and flaky' is a 'better or worse' body shape for living on twigs than 'flat and grey'. Instead, each lichen will be following some complex survival strategy with multiple factors and tradeoffs. Viewed in this way, although two lichens have met on a twig in photo 1, viewed over extended time, the 'trajectory' of their lives is no doubt entirely different. The forms they have will be because these are the forms that best befit them to their individual, distinct, extended, life styles.

My great pleasure in researching this blog is that through it my view of my garden grows richer all the time. To my mind, no one has said it beter than Martin Luther

For in the true nature of things, if we rightly consider, every green tree is far more glorious than if it were made of gold and silver.