In an unperturbed spatial environment, a community starting from a high-density (∼105 total cells/mm2) confluent inoculum expanded to new territories (purple). Compared to ‘Center’, self-organization was significantly more in ‘Expanding front’. Consequently, the initially 1:1 : ratio changed in favor of cooperators as the community expanded outward but not in ‘Center’. Sections were collected from three independent communities. Using the Mann–Whitney U-test, the association indexes of the ‘Center’ and of the ‘Expanding front’ were significantly different (p = 4 × 10−4). Exp: experiment.
DOI:
http://dx.doi.org/10.7554/eLife.00960.020