generalised life-cycle

What is a nematode?

Generalised life-cycle: infective juveniles hatch from eggs and migrate to plant roots where they feed, develop through 4 larval stages before becoming adults. After fertilisation eggs are produced (images with permission Rothamsted Research).

"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."

Nathan Augustus Cobb, 1914

What is a nematode?

Nematodes are small, usually microscopic and less than one millimetre, thread-like organisms (also referred to as roundworms or eelworms) living in almost every conceivable aquatic environment. In soils they are hugely numerous, one metre square of chalk grassland in the UK contained ten million individuals made up from 154 different species. Nematodes are evolutionarily ancient pre-dating the migration of life onto land.

Technically they are pseudocoelomates and have a body plan of a tube within a tube. The outer tube has a cuticle secreted by the epidermis, that protects the nematode from the environment, and under which lies the musculature. The inner tube makes up the alimentary canal and has no musculature. The space between these two tubes is called the pseudocoelomic cavity which contains fluid which baths the internal organs and reproductive tract.

Nematodes can be free-living, feeding on bacteria and other microbes, or parasitic where they can be major constraints to the health of both plants and animals. Both groups have complex life-cycles and although most are sexually dimorphic (ie have both males and females) and reproduce sexually, many reproduce asexually, either parthenogenetically (females producing further females) or through self-fertilisation in the case of hermaphrodites.

The hermaphroditic nematode Caenorhabdits elegans is a free living nematode that feeds on bacteria and is an excellent organism for studying the genetics of development and, more recently, innate immunity and pathogenesis. It has a short generation time of 4 days, produces around 350 offspring and was the first multicellular organism to have its total genome sequenced. Its use in research is well recognised and six scientists (Sydney Brenner, John Sulston, Robert Horvitz, Craig Mellow, Andrew Fire and Martin Chalfie) have received Nobel Prizes establishing it as a model organism par excellence.

Nematode Movie

Caenorhabditis elegans
Movie clip of nematode "worms" on an agar plate

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Download the nematode movie clip (.wmv)

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