Data from: Cooperation-mediated plasticity in dispersal and colonization

Kin selection theory predicts that costly cooperative behaviors evolve
most readily when directed toward kin. Dispersal plays a controversial
role in the evolution of cooperation: dispersal decreases local population
relatedness and thus opposes the evolution of cooperation, but limited
dispersal increases kin competition and can negate the benefits of
cooperation. Theoretical work has suggested that plasticity of dispersal,
where individuals can adjust their dispersal decisions according to the
social context, might help resolve this paradox and promote the evolution
of cooperation. Here, we experimentally tested the hypothesis that
conditional dispersal decisions are mediated by a cooperative strategy: we
quantified the density-dependent dispersal decisions and subsequent
colonization efficiency from single cells or groups of cells among 6
genetic strains of the unicellular Tetrahymena thermophila that differ in
their aggregation level (high, medium and low), a behavior associated with
cooperation strategy. We found that the plastic reaction norms of
dispersal rate relative to density differed according to aggregation
level: highly aggregative genotypes showed negative density-dependent
dispersal, whereas low-aggregation genotypes showed maximum dispersal
rates at intermediate density, and medium-aggregation genotypes showed
density-independent dispersal with intermediate dispersal rate. Dispersers
from highly aggregative genotypes had specialized long-distance dispersal
phenotypes, contrary to low-aggregation genotypes; medium-aggregation
genotypes showing intermediate dispersal phenotype. Moreover, highly
aggregation genotypes showed evidence for beneficial kin-cooperation
during dispersal. Our experimental results should help to resolve the
evolutionary conflict between cooperation and dispersal: cooperative
individuals are expected to avoid kin-competition by dispersing long
distances, but maintain the benefits of cooperation by dispersing in small
groups.