Monday, September 28, 2009

A microscopic Peritrichia Cillate (Vorticella?)

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

Readers of my blog may recall that some time ago I decided to investigate the microscopic inhabitants of some rainwater that had collected in my garden. I was delighted at the time to discover some mobile little Haematoccus algae. Spurred on by this success I recently decided to revisit a similar puddle.

This time the water was in shade and contained quantities of decaying leaf-matter. Placing a few drops under my micro- scope I saw nothing at first, but then began to notice numerous small, semi-transparent, stalked objects, such as those above the number '3' in the microscope photo 1 (click to enlarge). My first guess was that these were some sort of fungal spores. Then one moved!

Zooming in (Photo 2) revealed an ovoid creature with a fringe of hairlike cilia at the front end. You can just about make out one poking out above '2.7' on the scale bar. These cilia were in constant motion and set up eddy currents in the water, drawing in small food particles as I watched.

The move- ments made by my creature were highly charac- teristic. Any small distur- bance (such as a tapping the micro- scope slide) caused the stalk supporting the 'head' to rapidly contract, jerking the head backwards in the blink of an eye and at the same time changing the head-shape from ovoid to compact and spherical. Gradually over a period of perhaps half-a-minute the stalk would re-extend and the head return to its original shape.

My creature had one further surprise in store: I was amusing myself tapping the slide and watching the response, when, as if grown tried of my irritating presence, one of my little creatures suddenly detached itself from it's stalk and swam away!

I'm in possession of a nice introductory, colour Guide to Microlife (Rainis and Russell, Grolier Publishing) and I was relatively quickly able to identify my lifeform as a ciliate, the cilophora being a large collection ('phylum') of microscopic animals belonging to the even larger collection of microscopic animals, the protists (to get an idea of just how large you might like to peruse the 81,000 (!) images on the Protist database.)

Fortunately, the structure and habits of my creature allowed for some further progress: the presence of a contractile stalk, the cilia around the mouth and the fact that my little critter was able to swim free of its stalk all point to it being a member of the smaller (though still sizeable) subclass of organisms the peritrichia (which I read is from the Greek, peri=near, trichia=hair).

Now, had I observed any 'stalks' with more than one 'head', that might have narrowed things down to my creature being in the genus Epistylis. I didn't (though of course absence of evidence isn't evidence of absence), which finally brings me to the (somewhat tentative) conclusion that my little creature is a member of the genus Vorticella. Unfortunatly that's as far as I've got. There are a more than a dozen species in this genus and which mine is I can't tell. I'll be happy if anyone out there can tell me.

Naturally, I'm not the first microscopist to observe Vorticella and a little web browsing led me to two very nice articles (here and here) for the amateur. The latter includes some excellent photos including some of Vorticella reproducing by asexual budding. From these and other sites I also learn that a free swimming Vorticella 'head' is termed a telotroch and the stalk is able to contract by virtue of a contractile bundle of threads within termed a moneme. A paper by Sotelo and Trujillo-Cenoz (available to download here) has some ultra-high magnification electron-microscope photos of this and also reveals that the moneme is responsible for the shape-change the head suffers when the stalk contracts.

On the subject of cilia a quick web search turned up numerous papers and articles. My intention was talk about some here, but since I've already gone on for some length in this posting, and since I'm certain to have another opportunity to discuss cilia in the future (so many microscopic creature have them), I'll leave the topic for now.

Instead I'll end with a photo of a free-swimming little animal I encoun- tered in the same sample of water. The ident- ification of this one defeated me. Am I looking at a free swimming Vorticella or is this something else? If you know do please leave a comment.

Saturday, September 26, 2009

Couch Grass (Elymus elegans) and Perennial Ryegrass (Lobium perenne)

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

Success in discovering the identity of some plant or animal is all about the careful and methodical observation of details. I've written this before, and had I only paid attention to my own dictum, I might avoided wasting half a morning recently getting thoroughly confused over the species of some grass growing in a corner of my garden!

Intrigued by a comment in a booklet Practical Microscopy (Eric Marson, Northern Biological Supplies) - a superb guide I cannot recommend too highly to any amateur interested in preparing their own high quality microscope slides - I had set out to examine some blades of grass under my microscope.

Venturing into my garden I came across the grass in photo 1. The long, seed bearing structure is technically termed a 'spike'. I picked a little and came back inside but before putting it under the microscope I decided to try identifying the species using my copy of Grasses (Fitter publ. Collins). Having only a few inches of specimen, it wasn't long before I was stuck however. I went back outside therefore, found my clump of grass and picked a little more. Embassingly foolish as it seems now, this went on for nearly an hour, with me traipsing back and forth, collecting a little more grass each time and returning inside only to find myself more confused than ever.

Finally, in exas- peration, I threw away my growing collection of tattered grass cuttings and started a fresh, and this time, methodical study. The result was the arrangement in photo 2 and the belated realisation I'd been collecting bits of two different grasses!

The two in question are Couch grass (Elymus repens) (photo 2, upper) and Perennial Ryegress (Lolium perenne). Laid out neatly in photo 2 the differences are obvious. I can say that it underlines the lesson that one cannot trust that causal glance at that seemingly undifferentiated clump of 'spike bearing' grass swaying in the breeze!

One difference between the two grasses in photo 2 is leaf size. In fact however, this is not an overly useful guide to species identification, as the size of the leaf baldes can vary with their position on the 'stalk' (culm) and other factors (soil quality etc.). Instead, amongst the most useful guides to a grass's species is the shape and size of the ligule, a small vestigial leaf-like structure the nestles between the culm and a leaf. Photo 3 shows the ligule of Perennial Ryegrass. By contrast, Couch grass lacks a ligule (though just to confuse the unwary, the leaves wrap around the culm via two little sheath-like flaps know as auricles - see photo 4).

Returning to the spikes of my two grasses, photo 5 shows a closeup of both. These bear the grasses' minute flowers (the source of all that hayfever-inducing pollen in summer). As I learnt in my previous study of the Cultivated Oat (Avena sativa), the structure of grass flowers comes with a lot of botanical jargon. I'll not repeat it here, but for completeness I've labelled up photo's 6 and 7.

And what of that micro scope image I originally set out to acquire? Well, as everyone knows you can get a painful cut from the edge of a blade of grass. Putting one under the micro scope (photo 8) shows just why: a margin decorated with a row of tiny saw-toothed daggers. Another of nature's tiny miracles.

Saturday, September 19, 2009

Common Wasp Vespula vulgaris

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

Not everyone's favourite insect it must be admitted, photo 1 shows two wasps feeding on a rotten apple on my lawn (a habit shared with the mucor moulds I blogged previously).

The species here is the Common Wasp (Yellowjacket to those of you reading in the States) Vespula vulgaris, one of eight British species in the Vespidae family of social wasps. The hornet I blogged previously is another.

A number of the British social wasps are superficially rather similar and it can pay to take a close look at the face (photo 2) to be confident of the species. Were my wasp to be the not-uncommon German Wasp (Vespula germanica), for example, then it would have three little black dots in the centre of its face (mine doesn't). You can find a nice set of photos of the various British Vespidae species here.

Photo 2 also reveals my wasp is female: Her antennae have 12 segments (males have 13).

Wasps have been very common in my garden in recent summers and this is no doubt partly explained by the impressive abandoned nest (photo 3) I found in attic last winter.

Wasps have two pairs of wings, with each pair comprising a larger- and smaller wing. A pair gets 'zipped' together when the wasp lands so that it appears to be only a single wing. You can see this in photo 1. Taking one of the smaller wings and putting it under the microscope reveals that the analogy to a zip is well chosen: a row of hooks lines the edge of the smaller wing, allowing it to hook tightly onto the larger. Personally I never tire of looking at structures like this under the microscope. Any engineer will tell you how enormously demanding it is to machine mechanical devices to micron accuracy, yet mother nature is routinely able to grow fantastically intricate structures out of such unpromising materials as chitin or cellulose.

My efforts to learn something about Common Wasps led me back to the subject of 'worker policing', which you may recall I touched on in my posting on hornets. Briefly, it turns out that female workers in the colonies of many types of social wasp, bee and ant permit only eggs from the queen to hatch. Eggs laid by female workers are removed from the colony by other workers before they hatch. To the evolutionary biologist, this begs the simple question 'why?'. What advantage does the colony gain by only tolerating the eggs of a single individual (the queen)? Many learned papers have been written on this subject and I wouldn't presume a detailed understanding of all the technicalities but in brief, I understand the reason relates to so called 'kin selection'. It turns out that as a female worker, you are more likely to be closely genetically related to a grub hatching from a queen's egg than you are to one from the egg of fellow worker. Maximising all individuals' relatedness to each other is therefore achieved by preferentially rearing the queen's eggs.

Now, all of the above is as I explained it in my hornet posting. Whilst I didn't doubt the explanation, what I'd struggled to do there was to understand for myself in simple terms precisely why workers relate more closely to the queen's egg than to those of their sisters. In preparing this posting however, I came across the commendably readable More Than Kin and Less Than Kind by Douglas W. Mock. The key information I'd been missing concerns the way in which genes are passed down the generations in these many insects. Firstly it turns out what whilst female wasps each carry two sets of chromosomes (making them 'diploid' - just like us), males carry only a single set (they're haploid). Secondly it transpires that queens in insect colonies that practise worker policing, typically mate with multiple males. The sperm from all the queen's male partners is mixed together and stored in a vessel inside her body known as the spermatheca until needed to fertilise an egg. Which male's sperm fertilises which egg is then random. Taking these two facts together (the haploid/dipoloid male/female divide and the queen's 'random polygamy'), and working through some relatively simple genetics (anyone who remembers Mendel's sweet peas from school biology lessons should follow it), its not too hard to follow the chain of logic that shows that as a female worker born to a queen, you'll have a closer genetic resemblance to eggs from your mother than you will to eggs from your sisters.

And finally, I learn from a paper by Landolt that a good way to attract Vespula vulgaris wasps is to fill a vessel with acetic acid and isobutanol... of course, alternatively you might simply try eating a sandwich in your garden in August!