Clonal-aggregative multicellularity tuned by salinity in a choanoflagellate

Abstract Multicellularity evolved independently multiple times in eukaryotes 1–4 . Two distinct mechanisms underpin multicellularity 5 : clonality (serial cell division without sister-cell separation) and aggregation (whereby independent cells assemble into a multicellular entity). Clonal and aggregative multicellularity are traditionally considered to be mutually exclusive 1,6–8 , with rare exceptions 9 , and evolutionary hypotheses have addressed why multicellularity might diverge towards one or the other extreme 3,4 . Both animals and their sister group, the choanoflagellates, are currently known to acquire multicellularity only clonally 4,10,11 . Here we show that the choanoflagellate Choanoeca flexa 12…