They also knew that in the wild, the amoebae in fruiting bodies are close kin if not clones.
What prevents cooperation in wild populations from degenerating into the laboratory free-for-all?
Could the difference be that the amoebae in the laboratory were distant relations and those in the wild are kissing kin?
Suppose, the scientists thought, one amoeba ventured alone into a pristine field of bacteria.
As it grew and multiplied, making copies of itself, how long would it take for cheating mutations to appear or what was the mutation rate? Additionally, how successfully would these mutations proliferate--how strongly would they be selected?
To establish the mutation rate, Strassmann and Queller along with graduate student Sara Fox ran what's called a mutation accumulation experiment.
In this experiment, amoebae that mutated didn't have to compete against amoebae that were faithful replicators.
In the absence of selection, all but the most severe mutations were also reproduced and became a permanent part of the lineage's genome.
The scientists allowed 90 different lines of amoebae to accumulate mutations in this way.
"At the end," says Queller, "we found that among those 90 lines not a single one had lost the ability to fruit. So that's almost 100 lines, almost a thousand generations and 100,000 opportunities, to lose fruiting and none of them did.
"That allowed us, using statistics, to put an upper limit on the rate at which mutations turn a cooperator into an obligate cheater."
The rate was low enough that if fruiting bodies were forming in the wild from amoebae that were all descended from one spore, cheating would never be an issue.
But the scientists wanted to ask another, bigger question.
They used calculations invented for population genetics t
|Contact: Cheryl Dybas|
National Science Foundation