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Social Amoeba Answer Age-Old Question: Do Cheaters Always Win?

The social amoeba Dictyostelium discoideum has two life stages. When nutrients are plentiful, Dicty live as individuals but when starvation sets in, thousands of Dicty come together to form a fruiting body. This fruiting body is made up of a stalk that holds up a ball of spores, and this is where the cheating comes in — only cells that make it to the top of the fruiting body and become a spore get to live and pass on their genetic information.

It has long been known that Dicty cheat but it was unclear whether, in the wild, cheaters had a leg up on their non-cheating counterparts. Using next-generation sequencing to look at polymorphisms in social genes, scientists at Washington University in St. Louis now show that cheating is not always the winning strategy. Instead of taking over, cheaters have battled non-cheaters to a stalemate that maintains both cheaters and cooperators in a population.

Such stalemates are often found in complex environments where a given phenotype may not always be the most advantageous. The Dicty stalemate suggests that as cheaters take over a population their winning strategy begins to fail. Whether this is because the population runs out of cooperating stalk cells to support the cheating spores or whether there is a critical cheating population density that begins to put pressure on cooperative cells, is unclear. These results do however show that, at least in the world of social amoeba, in the long run it’s just as advantageous to be social as it is to be a cheating spore.

Source: Washington University in St. Louis

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