title: A shift from magnitude to sign epistasis during adaptive evolution of a bacterial social trait.
abstract: Although the importance of epistasis in evolution has long been recognized, remarkably little is known about the processes by which epistatic interactions evolve in real time in specific biological systems. Here, we have characterized how the epistatic fitness relationship between a social gene and an adapting genome changes radically over a short evolutionary time frame in the social bacterium Myxococcus xanthus. We show that a highly beneficial effect of this social gene in the ancestral genome is gradually reduced--and ultimately reversed into a deleterious effect--over the course of an experimental adaptive trajectory in which a primitive form of novel cooperation evolved. This reduction and reversal of a positive social allelic effect is driven solely by changes in the genetic context in which the gene is expressed as new mutations are sequentially fixed during adaptive evolution, and explicitly demonstrates a significant evolutionary change in the genetic architecture of an ecologically important social trait.
authors.affiliation: Department of Biology, Indiana University, 1001 E. Third Street, Bloomington, Indiana, 47401. peterzee@stanford.edu.
authors.forename: Peter C
authors.initials: PC
authors.lastname: Zee
authors.forename: Helena
authors.initials: H
authors.lastname: Mendes-Soares
authors.forename: Yuen-Tsu N
authors.initials: YT
authors.lastname: Yu
authors.forename: Susanne A
authors.initials: SA
authors.lastname: Kraemer
authors.forename: Heike
authors.initials: H
authors.lastname: Keller
authors.forename: Stephan
authors.initials: S
authors.lastname: Ossowski
authors.forename: Korbinian
authors.initials: K
authors.lastname: Schneeberger
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Velicer
mesh_terms: D000222:Adaptation, Physiological; D005075:Biological Evolution; D004843:Epistasis, Genetic; D056084:Genetic Fitness; D009068:Movement; D009154:Mutation; D016941:Myxococcus xanthus / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology
keywords: Adaptation; epistasis; experimental evolution; mutations; sociality