title: Rapid and widespread de novo evolution of kin discrimination.
abstract: Diverse forms of kin discrimination, broadly defined as alteration of social behavior as a function of genetic relatedness among interactants, are common among social organisms from microbes to humans. However, the evolutionary origins and causes of kin-discriminatory behavior remain largely obscure. One form of kin discrimination observed in microbes is the failure of genetically distinct colonies to merge freely upon encounter. Here, we first use natural isolates of the highly social bacterium Myxococcus xanthus to show that colony-merger incompatibilities can be strong barriers to social interaction, particularly by reducing chimerism in multicellular fruiting bodies that develop near colony-territory borders. We then use experimental laboratory populations to test hypotheses regarding the evolutionary origins of kin discrimination. We show that the generic process of adaptation, irrespective of selective environment, is sufficient to repeatedly generate kin-discriminatory behaviors between evolved populations and their common ancestor. Further, we find that kin discrimination pervasively evolves indirectly between allopatric replicate populations that adapt to the same ecological habitat and that this occurs generically in many distinct habitats. Patterns of interpopulation discrimination imply that kin discrimination phenotypes evolved via many diverse genetic mechanisms and mutation-accumulation patterns support this inference. Strong incompatibility phenotypes emerged abruptly in some populations but strengthened gradually in others. The indirect evolution of kin discrimination in an asexual microbe is analogous to the indirect evolution of reproductive incompatibility in sexual eukaryotes and linguistic incompatibility among human cultures, the commonality being indirect, noncoordinated divergence of complex systems evolving in isolation.
authors.affiliation: Institute for Integrative Biology, ETH Zürich, 8092 Zürich, Switzerland; olaya.rendueles@env.ethz.ch.
authors.forename: Olaya
authors.initials: O
authors.lastname: Rendueles
authors.affiliation: Department of Biology, Indiana University, Bloomington, IN 47405; Department of Biology, California State University-Northridge, Northridge, CA 91330;
authors.forename: Peter C
authors.initials: PC
authors.lastname: Zee
authors.affiliation: Department of Evolutionary Biology, Max-Planck Institute for Developmental Biology, 72076 Tübingen, Germany.
authors.forename: Iris
authors.initials: I
authors.lastname: Dinkelacker
authors.affiliation: Institute for Integrative Biology, ETH Zürich, 8092 Zürich, Switzerland;
authors.forename: Michaela
authors.initials: M
authors.lastname: Amherd
authors.affiliation: Institute for Integrative Biology, ETH Zürich, 8092 Zürich, Switzerland;
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wielgoss
authors.affiliation: Institute for Integrative Biology, ETH Zürich, 8092 Zürich, Switzerland; Department of Biology, Indiana University, Bloomington, IN 47405; Department of Evolutionary Biology, Max-Planck Institute for Developmental Biology, 72076 Tübingen, Germany.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Velicer
mesh_terms: D000222:Adaptation, Physiological; D005075:Biological Evolution; D002678:Chimera; D016941:Myxococcus xanthus / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D010641:Phenotype; D013997:Time Factors
keywords: cooperation; kin recognition; nonself recognition; social evolution; territoriality