Article: The selfish gene that learned to cooperate

The selfish gene that learned to cooperate

Kurt Kleiner

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."


Source: New Scientist (Open Access)
http://tinyurl.com/s7ekm

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Robert Karl Stonjek


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