By fostering freeloaders, charitable yeast cells put their communities at risk.
Alvaro Sanchez and Jeff Gore of the Massachusetts Institute of Technology in Cambridge engineered yeast to be either generous cells, which break down complex sugars to forms that are available to the community; or cheating cells, which rely on others for fuel. When the two strains were mixed in different ratios, the researchers found that — over many generations — large, stable populations formed in which less than 10% of the yeast population could support an overwhelming majority of freeloaders. However, these mostly mooching communities were prone to extinction: when the researchers simulated environmental disturbance by diluting the populations, they crashed. Such dynamics could help biologists to explain the evolution and variation seen in cooperative communities.