Making the ultimate family sacrifice( HOUSTON -- (Nov. 25 2008) -- There i...)

HOUSTON -- (Nov. 25, 2008) -- There is no greater sacrifice than giving one's life for others, and a new study by Rice University biologists and Baylor College of Medicine (BCM) geneticists is helping narrow the search for genes that drive single-celled amoebae to stick close to their kin before altruistically giving their all.

The study, which appears this week in PLoS Biology, focuses on the soil-dwelling amoeba Dictyostelium discoideum. These single-celled creatures eat bacteria, and as long as food is plentiful, they're content to live alone. But when food is scarce, D. discoideum band together by the thousands. About 20 percent of colony members sacrifice themselves to form a stiff stalk that the rest can climb to migrate and form a new colony elsewhere.

This altruistic behavior is a challenge for evolutionary biologists. Why, for example, haven't cheaters -- amoebae who avoid the stalk and focus all their energies on getting into the new colony -- squeezed out their altruistic brethren? What are the genetic checks and balances that guard against cheating?

"They seem to care how genetically similar their partners are," study co-author David Queller said of the new findings. "That's something that you see in other social organisms, and you'd expect to see it from theory, but it's still kind of surprising to see that behavior in an amoeba."

Queller, Rice's Harry C. and Olga K. Wiess Professor of Ecology and Evolutionary Biology, and colleagues examined how much mixing occurred between 16 strains of D. discoideum. The genetic similarities between strains varied, and the tests revealed that the more genetically akin two strains were, the more they mixed and worked together during colony formation.

Rice postdoctoral researcher Elizabeth Ostrowski, the study's lead author, said a number of studies have previously shown that genetically dissimilar strains of D. discoideum sometimes li
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