Figure 6. Synergy of different paths to multicellularity in K. lactis.

Blue, red and violet cells indicate non-flocculent snowflakes, flocculent unicells and flocculent snowflakes, respectively, and different shades denote distinct genotypes within each phenotype. (a) Snowflake clusters form by cell proliferation, resulting in discrete groups of permanently attached clonemates. (b) Yeast flocs arise through reversible social aggregation, resulting in social groups that may include different genotypes. (c) Flocculation is accelerated by multicellular clusters, amplifying and extending benefits of cluster formation. The settling velocity of snowflake clusters increases through floc-mediated cooperation with neighbouring snowflakes; however, cooperative settling may also benefit flocculent unicellular free riders. (d) Synergy between cluster and floc formation increases the extent of settling after 7 m in derived K. lactis suspensions. Bold numbers indicate treatments with significant settling (matched pairs t-test, n=3, P<0.05) and letters denote statistically different groups (Tukey's HSD, n=12, P<0.0001) after 7 m. Flocculation significantly increases settling in multicellular populations (P<0.0001), but does not influence settling in unicellular populations over the duration of standard settling selection (P=1).