Wonderful world of nematodes

[Rolfe]

Once upon a time, a very long time ago now, when I was a lowly undergraduate, I remember a lecturer saying that if you took all the matter away from the earth except what makes up nematode worms, a ghostly outline of everything would still be visible - plants, animals, everything.

Later, when I thought about it (and after having looked down rather a lot of microscopes at any magnification you care to name and not been struck by the plethroa of nematodes), I wondered if I'd mis-heard, and maybe he had said bacteria? Because the more I thought about it, the less likely it seemed.

But then a few years ago I happened to look at one of my textbooks from those far-off days, and there was the actual statement. Not bacteria, nematodes. I realised I hadn't misheard, but still shrugged it off as somebody must have been mistaken.

However, yesterday I idly Googled "nematode", just looking for an exact definition for a report, and hit on the Wikipedia article on the subject.

Quote:

If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes and oceans represented by a thin film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.

This statement is credited to one N. A. Cobb, in 1914 edition of the Yearbook of the United States Department of Agriculture. Now I'm not disputing that nematodes are abundant, or that they are adapted to many ecological niches, or that practically every species has its own species of nematodes adapted to parasitise on it, or that there are a lot of the things in the earth and in the water.

However, take away everything else, and you would still see rows of trees, and all plants and animals? I note that the exact wording is a bit vaguer than I recalled, but still? Most animals I examine are not parasitised, and any time I've looked at a plant under the microscope I've quite failed to be impressed by all the little wriggly worms down there.

Does this sweeping statement, from almost 100 years ago, deserve the prominence it has in the Wiki article, and the mention it got in the textbook, and in the lecture I attended? I think it's a gross exaggeration.

Rolfe.

[Jimcalagon]

Another question, why do British speakers of English pronounce 'nematodes' as 'nemmatodes' and americans 'neematodes' ?

[fuelair]

Originally Posted by Jimcalagon

Another question, why do British speakers of English pronounce 'nematodes' as 'nemmatodes' and americans 'neematodes' ?

I fear I cannot help on that since A)I am American but B) have never heard it pronounced other than "nemmatodes" except by students unfamiliar with the term. (My undergraduate degree is Biology.)

[Piscivore]

Wouldn't they fall down?

[fls]

I remember being told the same thing in one of my medical school lectures.

Linda

[Jimcalagon]

Originally Posted by fuelair

I fear I cannot help on that since A)I am American but B) have never heard it pronounced other than "nemmatodes" except by students unfamiliar with the term. (My undergraduate degree is Biology.)

That might explain it... I know I have heard Americans refer to them as neematodes a number of times but the only specific occasion I can think of was the episode of Spongebob where his house is eaten by an infestation of neematodes.

Were they mentioned in an episode of the X-Files as well?

[Ivor the Engineer]

Originally Posted by Rolfe

Once upon a time, a very long time ago now, when I was a lowly undergraduate... almost 100 years ago...

Seriously, given that the crust of the earth makes up such a tiny proportion of its mass (0.5%), and of that, much of it's in places no nematode worm has ever gone, I think the statement is misleading.

http://www.amonline.net.au/geoscienc.../structure.htm

Having said that...

http://www.path.cam.ac.uk/~schisto/G...helminths.html

Quote:

Enterobius vermicularis - Pinworm, Threadworm.

An extremely common nematode infection, particularly in temperate areas such as Western Europe and North America, (it being relatively rare in the tropics) and particularly in children. It has been estimated that the annual incidence of infection is over 200 million, this probably being a conservative figure. Samples of caucasian children in the U. S. A. and Canada have shown incidences of infection of fro 30% to 80%, with similar levels in Europe.




Ascaris lumbricoides - The Large Human Roundworm.

Again the incidence rates for this parasite are very high with > 1500 million cases of infection annualy, of which ~210 million of these cases are symptomatic (* but see below).




Trichuris trichuria - The Large Human Roundworm.

The incidence rates for this parasite are also very high, with estimates of ~1300 million cases of infection annualy, of which >133 million of these cases are symptomatic (* again but see below).




The Hookworms .

These are represented by two parasites, Necator americanus in the tropics and sub tropics worlwide and the S. E. states of the U. S. A., and Ancylostoma duodenale, again with a worldwide distribution in the tropics and sub tropics as well as the Mediterranean region. In the case of these parasites there are > 1200 million cases of hookworm infection annualy, of which ~100 million of these cases are symptomatic (* again, but see below).

[Deetee]

Originally Posted by Rolfe

....However, take away everything else, and you would still see rows of trees, and all plants and animals? I note that the exact wording is a bit vaguer than I recalled, but still? Most animals I examine are not parasitised, and any time I've looked at a plant under the microscope I've quite failed to be impressed by all the little wriggly worms down there.

Does this sweeping statement, from almost 100 years ago, deserve the prominence it has in the Wiki article, and the mention it got in the textbook, and in the lecture I attended? I think it's a gross exaggeration.

Rolfe.

Nematodes are certainly very abundant, and I have no problem with the idea that all virtually all soil and plant matter could be "outlined" in this way by free living nematodes, of which there are tens of thousands of different species (hear that young earthers?)

As regards animals, I am rather sceptical. Humans might well be outlined in bacteria, but not nematodes.

Whilst on the subject, I seem to recall an absolutely fascinating life cycle involving wasps and figs - Dawkins did a chapter in "Climbing Mt Improbable" on this.

Isn't nature (and evolution) marvellous?

[fuelair]

Why, yes, yes they both are!!!

[XBoxWarrior]

I need to call the Fumigator........

My house is infested.........damn nematodes, have ruined my sofa, and the carpet in the basement.

My "new" goal in life is to kill the nematodes.

Hope I sleep better.

Maybe this is my philosophical dilema?

[CapelDodger]

Originally Posted by Deetee

Nematodes are certainly very abundant, and I have no problem with the idea that all virtually all soil and plant matter could be "outlined" in this way by free living nematodes, of which there are tens of thousands of different species (hear that young earthers?)

The nematodes' name is Legion. Beetles have hit on a winning basic platform as well - thousands of species. Genus Homo? One species (until we gather in chimps, bonobos and gorillas for comfort as the darkness gathers ...)

Quote:

As regards animals, I am rather sceptical. Humans might well be outlined in bacteria, but not nematodes.

That rather depends on how dirty they are. There's nematodes in that there dirt. (And don't forget the clothes that dimly outline us.)

Quote:

Whilst on the subject, I seem to recall an absolutely fascinating life cycle involving wasps and figs - Dawkins did a chapter in "Climbing Mt Improbable" on this.

Isn't nature (and evolution) marvellous?

And won't those specialised wasps and figs go down the toilet of extinction together, come the next great cull?

Trees and wasps will carry on, of course. Lots of species there that are ready and able to diversify when opportunity presents.

[Kotatsu]

Originally Posted by Rolfe

However, take away everything else, and you would still see rows of trees, and all plants and animals? I note that the exact wording is a bit vaguer than I recalled, but still? Most animals I examine are not parasitised, and any time I've looked at a plant under the microscope I've quite failed to be impressed by all the little wriggly worms down there.

Does this sweeping statement, from almost 100 years ago, deserve the prominence it has in the Wiki article, and the mention it got in the textbook, and in the lecture I attended? I think it's a gross exaggeration.

I believe it is something of an exaggeration when it comes to most plants and animals, but it certainly is not an exaggeration for the rest. I had a PhD course in Meiofauna (1), and one of the lecturers was this very knowledgeable man from East Anglia somewhere. He was the foremost expert on nematodes in the world, or one of them, and he stated, if I recall correctly, that if you take any amount of soil and study it, you will find that it contains more nematodes than actual soil.

Nematodes are amazing creatures, which, as a group, displays one of the greatest diversities on Earth. Anyone who's got access to a good microscope should, at least once, go out and get some soil samples and sort them through. Unless I misremember, you can make quite good temporary slides if you just douse them briefly in glycerol. The hard part, if you take a soil sample from a marine or limnic environment, is to sort out all the other amazing creatures you could fine. Gastrotrichs, nematomorphs, Gnathostomulids, and so on...

On the same course, which was coupled to a workshop for some of the top experts in meiofauna of the world, we also had the opportunity to meet REinhardt Kristensen, a Danish scientist who has over his career discovered and described three new phyla of animals: Cycliophora, Micrognathozoa, and Loricifera. There is no doubt that several other, previously unknown, phyla still exist to be discovered in the seas.

---
(1) The fauna that is of sufficient size to move between grains of sand or clay without dislodging them too much. That is, not digging like worms, but sort of sliding between them in the thin films of water surrounding all earth aggregates in soil.

[Kotatsu]

Originally Posted by CapelDodger

That rather depends on how dirty they are. There's nematodes in that there dirt. (And don't forget the clothes that dimly outline us.)

Then there's that nematode which is endemic to beer mats (coasters?) in some parts of Eastern Europe. One of the most unusual niches I know of.

[Rolfe]

Nematode infection in animals is common in juveniles, but uncommon in healthy adults due to immune-mediated elimination. Most carcasses I open have nary a nematode in sight. Most faecal check tests are negative (though to be fair some of that is down to the use of anthelmintic drugs which were not around in 1914). Very very few adult people are going to be parasitised by nematodes, even though most people have never had an anthelmintuc treatment in their lives. Even where nematodes are present, they mainly reside in the gut (some favour the lungs), they are certainly not all-pervasive throughout the body.

When I read the exact wording of the original assertion is wasn't as specific as the later versions, in that he doesn't seem to be saying that we'd see the actual exact outlines of everything, but rather that clumps of nematodes (presumably originating from the guts) would show where there were "massings" of human beings. I think, really, we'd have to assume that it would be the children we'd be seeing that way, and only a proportion of these. Same would apply to animals.

I've never noticed any nematodes any time I've looked at a plant under the microscope so I'm not at all sure about the outlines of the trees. maybe a botanist could help? But certainly, I wasn't disputing the abundance in the soil. I wonder if Cobb started from there, and just added on the extra clustering of nematodes you'd probably find where there were large clusterings of animals?

I still think it's a bit of an exaggeration, and could probably be said with more truth about bacteria, but the original wording isn't quite as startling as the versions I'd picked up from the lecture and the textbook.

Rolfe.

[Deetee]

I love nematodes - the juicy big tropical ones that parasitise humans, that is. Being born in tropical Africa, I've had several myself, and have kept a keen interest in nematodes all my professional life (though in the UK there is less scope to do so in medical circles - you need to be a vet like Rolfe to get in on the act).

Another fascinating nematode - One that turns the ant it has parasitised into something that mimics a ripe berry, just so birds will eat it and complete the cycle.

Edited to remove my "hotlinked" pic.

[Kotatsu]

Originally Posted by Deetee

I love nematodes - the juicy big tropical ones that parasitise humans, that is. Being born in tropical Africa, I've had several myself, and have kept a keen interest in nematodes all my professional life (though in the UK there is less scope to do so in medical circles - you need to be a vet like Rolfe to get in on the act).

There is a group based somewhere in East Anglia, I think, who works with routine identification of nematodes and some environmental work using nematodes as model organisms, I think. I can't remember the name of the guy who had the lecture at the meiofauna course I mentioned, but I could look it up. He was very good at what he was doing.

[Pipirr]

Originally Posted by Rolfe

I've never noticed any nematodes any time I've looked at a plant under the microscope so I'm not at all sure about the outlines of the trees. maybe a botanist could help? But certainly, I wasn't disputing the abundance in the soil. I wonder if Cobb started from there, and just added on the extra clustering of nematodes you'd probably find where there were large clusterings of animals?

Oh, alright then. Nematodes cause most problems by attacking the roots of plants. They can parasitise the above ground plant tissues, and you can see nematode damage in leaves. But I think this is probably dependent on the plant species. A slow growing dicotyledon would be more likely to have above ground nematode parasites than a fast growing monocot. If you consider that a crop plant like wheat or barley can be putting up a new leaf every 48 hours, our nematode friends would have to be motoring along to parasitise the new leaf and colonise it. These leaves don't last all that long, either. Also, I don't think foliar nematodes can migrate through the internal tissues of the plant. They would need wet conditions to reach the leaves, or an insect vector.

So I think Cobb took some poetic license with the plants. Its hard to imagine the fast growing plants being so thoroughly colonised that, if you take away the plant tissue, the nematodes preserve the outline. Their roots, however, that's more believable.

[CapelDodger]

Originally Posted by Kotatsu

Then there's that nematode which is endemic to beer mats (coasters?) in some parts of Eastern Europe. One of the most unusual niches I know of.

Remarkable. I wonder how long it'll be before a sexually-transmitted sub-species emerges?

[CapelDodger]

Originally Posted by Pipirr

Oh, alright then. Nematodes cause most problems by attacking the roots of plants.

I'm sensing a rather negative attitude to nematodes. It's a big family, it has its rogue elements, but you have to look at the bigger picture. Nematodes contribute a lot to the soil that plants depend on.

Quote:

So I think Cobb took some poetic license with the plants. Its hard to imagine the fast growing plants being so thoroughly colonised that, if you take away the plant tissue, the nematodes preserve the outline. Their roots, however, that's more believable.

Leaves gather dust, so assuming that

Quote:

"If all the matter in the universe except the nematodes ..."

includes nematode eggs, which are on a dusty scale, maybe there would be a ghostly outline.