HOUSTON, July 5, 2007 -- No one likes a cheater, even a single-celled one.
New research from Rice University shows how cooperative single-celled amoebae rely on family ties to keep cheaters from undermining the health of their colonies. The research appeared in the Proceedings of the National Academy of Sciences in May.
"It's very unusual to get a complete story in biology -- one that marries careful field work with painstaking work in the laboratory -- and that's what we have here," said research co-author Joan Strassmann, chair of Rice's Department of Ecology and Evolutionary Biology.
Rice's research involved the common soil microbe Dictyostelium discoideum. These amoebae can be loners in times of plenty, but when food is scarce they work together, forming colonies to ensure their survival. About one fifth of the individuals in a colony form a tall, thin stalk. The rest climb the stalk and clump together into a bulbous fruiting body that can be carried away to better environs by the wind or on the legs of passing insects.
This simple social system poses an evolutionary conundrum for biologists; the members of the stalk give themselves up altruistically to support the colony, so what's to keep more selfish strains of D. discoideum from cheating the system, avoiding the stalk and out-reproducing their altruistic neighbors"
Strassmann and Rice evolutionary biologist David Queller have previously investigated how Dictyostelium colonies control cheating. For example, a study on D. discoideum showed that one gene governing cooperative behavior was also tied to reproduction. In another study, mutants that were genetically predisposed to avoid altruistic service in the stalk were also excluded from reproducing. A third study demonstrated that Dictyostelium purpureum preferentially associated with its own kin -- another mechanism that ensures altruism isn't taken advantage of by cheaters.