What unseen predator strangles its prey?

By Chelsie Vandaveer

November 7, 2001

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Nematodes are microscopic roundworms, unrelated to earthworms, which live in the soil. Some are beneficial to the gardener like those that eat detritus and recycle nutrients back into the earth. But there are those that eat into living roots. There is nothing worse than losing a prized plant or an entire crop to these ubiquitous bar sinisters. (See Renfield's Garden, October 3, 2001) But even nematodes have their predators.

In a group of fungi loosely known as deuteromycetes, it has been estimated that at least fifty species are predatory. The best studied of these is Arthrobotrys dactyloides, [ar throw' bot rees dak' til oy' des]. This quiet creeper has been well known for seventy years for its habit of strangling its prey.

The nematode is strangled almost before it knows it has been trapped.
Nematode Trapping Fungus
Photographic Print London Scientific Films
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Arthrobotrys dactyloides grows as slender hyphae (filaments) through the soil. Side branches of the filaments grow exactly three cells, the third connecting back to the first cell forming a ring or noose. When a nematode bungles into one of these nooses, it triggers receptors on the cells' surfaces to produce molecules called inositol-3-phosphate.

These molecules raise the calcium level inside the cells which opens aquaporins or water channels. Water floods into each cell swelling it to three times its original size in one-tenth of a second. The nematode is strangled almost before it knows it has been trapped. The fungus grows hyphae into the nematode and secretes digestive enzymes. After digestion, Arthrobotrys absorbs the nutrients.

The College of Agricultural and Environmental Sciences, University of Georgia has micrographs of a nematode trapped in the noose of Arthrobotrys dactyloides. To view the micrographs, click on the link:

http://www.cpes.peachnet.edu/nemabc/slide23.htm

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