title: Differential adhesion between moving particles as a mechanism for the evolution of social groups.
abstract: The evolutionary stability of cooperative traits, that are beneficial to other individuals but costly to their carrier, is considered possible only through the establishment of a sufficient degree of assortment between cooperators. Chimeric microbial populations, characterized by simple interactions between unrelated individuals, restrain the applicability of standard mechanisms generating such assortment, in particular when cells disperse between successive reproductive events such as happens in Dicyostelids and Myxobacteria. In this paper, we address the evolutionary dynamics of a costly trait that enhances attachment to others as well as group cohesion. By modeling cells as self-propelled particles moving on a plane according to local interaction forces and undergoing cycles of aggregation, reproduction and dispersal, we show that blind differential adhesion provides a basis for assortment in the process of group formation. When reproductive performance depends on the social context of players, evolution by natural selection can lead to the success of the social trait, and to the concomitant emergence of sizeable groups. We point out the conditions on the microscopic properties of motion and interaction that make such evolutionary outcome possible, stressing that the advent of sociality by differential adhesion is restricted to specific ecological contexts. Moreover, we show that the aggregation process naturally implies the existence of non-aggregated particles, and highlight their crucial evolutionary role despite being largely neglected in theoretical models for the evolution of sociality.
authors.affiliation: CNRS UMR 7625 Écologie et Évolution, École Normale Supérieure, Paris, France ; CNRS UMR 7625 Écologie et Évolution, Université Pierre et Marie Curie-Paris 6, Paris, France.
authors.forename: Thomas
authors.initials: T
authors.lastname: Garcia
authors.affiliation: Instituto de Física, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Leonardo Gregory
authors.initials: LG
authors.lastname: Brunnet
authors.affiliation: CNRS UMR 8197 INSERM U1024, Institut de Biologie de l'École Normale Supérieure (IBENS), Paris, France.
authors.forename: Silvia
authors.initials: S
authors.lastname: De Monte
mesh_terms: D000465:Algorithms; D001422:Bacterial Adhesion / Q000502:physiology*; D005075:Biological Evolution; D002448:Cell Adhesion / Q000502:physiology*; D019295:Computational Biology; D016837:Dictyosteliida / Q000502:physiology; D005716:Game Theory; D006801:Humans; D008954:Models, Biological; D009038:Motion; D009231:Myxococcales / Q000502:physiology; D012641:Selection, Genetic; D012919:Social Behavior