For cooperation to persist in the often violently competitive realm of bacteria, cheaters must be kept in line.
Two Indiana University Bloomington biologists have learned that in one bacterium, at least, bacterial cooperators can evolve to "police" the cheaters and arrest their bids for dominance.
"Even simple organisms such as bacteria can evolve to suppress social cheaters," said Gregory Velicer, who with Ph.D. student Pauline Manhes has reported the policing behavior in the Proceedings of the National Academy of Sciences.
Their laboratory experiments suggest that cooperative bacteria in nature may evolve to behave in ways that thwart the increase of selfish cheaters. In complex multicellular organisms such as ourselves, cancer cells can be viewed as cheaters that proliferate at the expense of the larger organism. If cancer cells are not successfully "policed" by our healthy cells (and/or medical intervention), the results can be catastrophic. Similarly, the long-term fate of cooperator lineages can be threatened by neighboring cheater lineages in the same social group unless the cooperators are able to migrate away from cheaters or evolve to suppress them.
"Mechanisms that prevent, mitigate or eliminate social conflict among interacting individuals are required for cooperation or multicellularity to succeed," Velicer said. "Policing is one such mechanism. This study shows that bacteria have the potential to evolve behaviors that eliminate fitness advantages derived from cheating within social groups."
Myxococcus xanthus is a predatory bacterium that swarms through soil, killing and eating other microbes by secreting toxic and digestive compounds. When food runs out, cells aggregate and exchange chemical signals to form cooperative, multi-cellular fruiting bodies. Some of the cells create the fruiting body's structure. Other cells are destined to become hardy spores that can survive starvation a
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