[Mike]

Slime mould
June 18, 2005

http://www.libraryjournal.com/article/CA608908.html

TAKE a walk in the garden or woods in early summer or autumn and you
may come across something on the ground that looks suspiciously like
dog sick. It may be dog sick, but equally it could be a slime mould,
a strange cross between an animal and a fungus that feeds on dead
grass or leaves and thrives in the ground’s moist warmth.

Why strange? Slime moulds are known as “social amoebas” but they
don’t behave like any other single-celled creature. The moulds are
hard to classify because their life cycle is similar to a fungus’s
(they reproduce via spores), but they share more genes with animals
than they do with, say, yeasts. We know about their animal genes
because we now have the complete genetic blueprint for Dictyostelium
discoideum, the most commonly studied slime mould (Nature, vol 435,
p 43).

And then there’s the outlandish way a slime mould hunts its prey. It
moves about the damp soil as a single blob of protoplasm with many
nuclei, gobbling up bacteria and particles of organic matter and
growing through simple cell division. Then, as its growth outstrips
its food supply, the creature sends out a chemical signal to other
slime moulds, which gather together to form a multicellular super-
organism. Covered in slime and often as big as a human hand, it
crawls through the forest in search of food, reaching a top speed of
about a centimetre an hour. Then, when resources run low, it finds a
sunny spot to bask and transforms itself into a spore factory,
dispersing its cells on the wind to better hunting grounds.

If you think that’s clever, consider this: slime moulds appear to
possess a basic intelligence. In 2000, researchers in Japan found
that a slime mould called Physarum polycephalum could navigate a
maze. They placed pieces of chopped-up slime mould in various
corners of a plastic maze with two openings where they left oat
flakes, a favourite food of slime moulds. The pieces of mould came
together to form a single organism, but instead of filling the maze
as the researchers had expected, the organism withdrew from dead
ends and formed a single tube spanning the shortest distance between
the two openings. “Clever and cunning” is how they described it.

How does an organism with no nervous system accomplish such a feat?
It may be related to the mould’s rhythmic contracting and relaxing
when it forms into a tube, and the way these pulses vary when it
comes into contact with food. Beyond that, where these enigmatic
creatures get their computing power from is still pretty much a
mystery.