"You're nothin' but cheatin' slime"

by David Sugarman

Slime moulds are definitely weird. They are slimy, but they aren't moulds. Most of the time, they live as free-living single cells that look like amoeba.

When conditions get tough — say, no food — thousands of different individual cells come together to form a visible blob called a slug (a new many-celled animal).

The cells at the front of the 'slug' act altruistically, giving up reproduction to become a slender stalk. This supports the remaining cells that become spores. The spores are resting stages that can be spread to where living conditions may be better for new slime mould cells.

Unlike those of most multicellular animals, the slug cells are genetically different, because the slug is a mix of individuals that are not all related to each other.

How do these cells 'decide' which will become stalk formers and which will become the lucky spore producers? We don't know, but it seems to be not all that friendly. Scientists in Texas have found that some cells actually cheat.

In most multicellular animals, cells cooperate. But scientists found that in a slime mould slug, some of the cells take advantage of others. To a slime mould cell, it's an advantage to become a spore, and not to be a stalk cell, which dies.

Some cells contribute less to stalk formation while forming more than their fair share of spores. The 'victim' cells form more of the stalk, helping to spread the cheater spores around.