Data from: The costs and benefits of multicellular group formation in algae

The first step in the evolution of complex multicellular organisms
involves single cells forming a cooperative group. Consequently, to
understand multicellularity, we need to understand the costs and benefits
associated with multicellular group formation. We found that in the
facultatively multicellular algae Chlorella sorokiniana: (1) the presence
of the flagellate Ochromonas danica or the crustacean Daphnia magna leads
to the formation of multicellular groups; (2) the formation of
multicellular groups reduces predation by O. danica, but not by the larger
predator D. magna; (3) under conditions of relatively low light intensity,
where competition for light is greater, multicellular groups grow slower
than single cells; (4) in the absence of live predators, the proportion of
cells in multicellular groups decreases at a rate that does not vary with
light intensity. These results can explain why, in cases such as this
algae species, multicellular group formation is facultative, in response
to the presence of predators.