The role of ecology in the evolution of multicellularity

The emergence of multicellularity was one of the major transitions in the
early evolution of life on earth. Particularly intriguing are those cases where
genetically heterogeneous complexes may be formed, among which cellular
slime molds are a paradigmatic example. In the absence of food, single cells
aggregate into a non-necessarily clonal multicellular fruiting body, where they
differentiate into dead stalk cells and reproductive spores. Such division of
labor promotes a strong selection to be represented in the reproductive spores
and should lead to a reduction in the genotypic diversity, which is inconsistent
with the great diversity found in nature. However, not all cells aggregate into
the fruiting body and we suggest that these non-aggregating cells provide an
additional fitness component that can resolve this inconsistency in two ways.
First, apparent reproductive skew in the spores of chimeric (heterogeneous)
fruiting bodies could simply be the result of different investments into spores
versus non-aggregators induced by different environmental conditions; and
second, in an ecosystem with multiple local environments coupled via weak-
to-moderate dispersal, coexistence of multiple genotypes can occur.



Reference:


Corina E. Tarnita, Alex Washburne, Ricardo Martinez-Garcia, Allyson E.
Sgro and Simon A. Levin. PNAS 112, 27762781 (2015).