Extended Data Figure 6: Cycling through phases.

Ancestral and derived lines differ in their capacity to transition between phases of the life cycle. Three replicate populations of the two ancestral and derived lineages with the highest fitness: 71, 73 and 16, 17, respectively, were founded by the representative WS type and plated to check for SM types. Whereas ancestral WS took 48 h to generate detectable levels of SM, the two derived WS populations contained a mixture of WS and SM colonies, such that even at the time of initial inoculation, both types were present. SM colonies were then used to found populations that were plated to check for WS types. Ancestral lineages 71 and 73 completed two cycles before extinction through failure to produce SM, whereas derived lines 16 and 17 completed five cycles before termination of the experiment. Colonies were photographed after 48 h of growth. Notable in the evolved lines is the visible presence of zones of SM cells surrounding the central WS colony.