title: Cooperation-mediated plasticity in dispersal and colonization.
abstract: 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 six 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.
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France. jacobstaffan@gmail.com.|Université Catholique de Louvain, Earth and Life Institute and Biodiversity Research Centre, Croix du Sud 4, L7-07-04, 1348, Louvain-la-Neuve, Belgium. jacobstaffan@gmail.com.
authors.forename: Staffan
authors.initials: S
authors.lastname: Jacob
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France.|Current Address: Landcare Research Manaaki Whenua, Private Bag 1930, Dunedin, 9054, New Zealand.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Wehi
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Clobert
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France.|Université Catholique de Louvain, Earth and Life Institute and Biodiversity Research Centre, Croix du Sud 4, L7-07-04, 1348, Louvain-la-Neuve, Belgium.
authors.forename: Delphine
authors.initials: D
authors.lastname: Legrand
authors.affiliation: Université Catholique de Louvain, Earth and Life Institute and Biodiversity Research Centre, Croix du Sud 4, L7-07-04, 1348, Louvain-la-Neuve, Belgium.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Schtickzelle
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France.
authors.forename: Michele
authors.initials: M
authors.lastname: Huet
authors.affiliation: Station d'Ecologie Théorique et Expérimentale du CNRS, UMR 5321, 09200, Saint-Girons, France.|Institute for Advanced Studies in Toulouse, Toulouse School of Economics, 21 allée de Brienne, 31015, Toulouse, France.
authors.forename: Alexis
authors.initials: A
authors.lastname: Chaine
mesh_terms: D005075:Biological Evolution; D002449:Cell Aggregation / Q000235:genetics; D005838:Genotype; D008957:Models, Genetic; D016808:Tetrahymena thermophila / Q000235:genetics* / Q000502:physiology
keywords: Altruism; colonization; cooperation; density-dependent dispersal; kin selection; mobility; reaction norms; social aggregation