TY - JOUR T1 - Hard and Soft Selection in the Laboratory: Dissecting the Mechanisms of Polymorphism Maintenance in Spatially Heterogeneous Environments JF - bioRxiv DO - 10.1101/100743 SP - 100743 AU - Romain Gallet AU - Rémy Froissart AU - Virginie Ravigné Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/03/19/100743.abstract N2 - Predicting and managing contemporary adaption requires a proper understanding of the determinants of genetic variation. Spatial heterogeneity of the environment may stably maintain polymorphism when habitat contribution to the next generation can be considered independent of the degree of adaptation of local populations within habitats (i.e., under soft selection). In contrast, when habitats contribute proportionally to the mean fitness of the populations they host (hard selection), polymorphism is not expected to be maintained by selection. Although mathematically established decades ago, this prediction had never been properly explored. Here we provide an experimental test in which polymorphic populations of Escherichia coli growing in heterogeneous habitats were exposed to hard and soft selection regimes. As predicted by theory, polymorphism was longer preserved under soft selection. Complementary tests established that soft selection slowed down fixation processes and could even protect polymorphism on the long term by providing a systematic advantage to rare genotypes. ER -