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New Scientist
August 12, 2006
SECTION: NEWS; This Week; Pg. 13

LENGTH: 414 words

HEADLINE: The selfish gene that learned to cooperate

BYLINE: Kurt Kleiner

BODY:


GENES are famously selfish, but they can also be sweetly cooperative. Now for the first time a gene for altruism has been discovered that smooths the cooperation necessary for cells to live together.

The gene, called regA , helps a unicellular green alga survive a hostile environment and also helps cells in a related, multicelled alga cooperate. The research provides insight into how unicellular organisms might originally have developed into multicelled organisms, and into the genetic basis of social behaviour.

Volvox carteri is a green alga made up of about 2000 small cells arranged in a ball, and 16 much larger reproductive cells. The small cells cannot divide, and instead devote their energy to propelling the organism through the water with their flagella.

When V. carteri reproduces, the cells divide asymmetrically, so that the daughters also end up with a few large cells that are capable of reproducing and thousands of small cells that are not. It's a novel example of reproductive altruism, in which an individual - in this case a cell - gives up the chance to reproduce in order to increase the reproductive fitness of others that share some or all of its genes. The regA gene stops the small cells from reproducing by suppressing formation of new chloroplasts and preventing the cells from growing large enough to divide.

But how is the cooperative gene linked to a selfish one? Aurora Nedelcu of the University of New Brunswick in Fredericton, Canada, and Richard Michod of the University of Arizona, Tucson, found a similar gene in Chlamydomonas reinhardtii , a green alga that lives as a single cell. In C. reinhardtii , however, regA is switched on only during harsh environmental conditions, such as a lack of sunlight or nutrients. The gene apparently helps the alga conserve energy and survive during lean times, giving it a better chance of living to reproduce under better conditions (Molecular Biology and Evolution , vol 23, p 1460).

At some point, a mutation seems to have occurred which turned the selfish gene into a cooperative one, and made it possible for V. carteri to develop specialised cells. Nedelcu says analogous processes might have allowed other multicellular organisms to develop from unicellular organisms.

"It's an important step forward," says Gene Robinson, a biologist at the University of Illinois in Urbana-Champaign. "The evolutionary roots of altruism have been functionally traced from a solitary species to a more social species."

LOAD-DATE: August 12, 2006