In new research, evolutionary biologists and geneticists at Rice University and Baylor College of Medicine have isolated a genetic mechanism that counters competitive pressures and stabilizes cooperation. Their research appears in the Oct. 7 issue of the journal Nature.
Using the latest tools of molecular genetics, the researchers found that the phenomenon known as pleiotropy -- which occurs when a gene affects more than one inherited trait -- plays a crucial role in preventing "cheaters" from exploiting their neighbors within slime mold colonies that are formed by the social amoeba Dictyostelium discoideum.
"What we've found is a molecular block to cheating and the genetic mechanism it relies on-- tying cooperative genes tightly with the essential function of reproduction," said paper co-author Joan Strassmann, professor of ecology and evolutionary biology at Rice. "Such a mechanism makes the loss of social genes costly to cheaters, and we believe this pleiotropic mechanism may be indicative of a general mechanism that's employed in many species to stabilize cooperation."
The Rice-Baylor experiments draw upon one of the most extraordinary examples of social cooperation among microorganisms: when slime mold amoebae run out of the bacteria they eat, they group, then form a fruiting body in which about one-fifth of the single-celled individuals within the colony sacrifice themselves to form the stalk that holds up the spores.
Before forming a stalk, the colony goes through a stage where it forms a slug-like structure. During this stage, cells produ
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