Large global effective population sizes in Paramecium

Abstract

The genetic effective population size (Ne) of a species is an important parameter for understanding evolutionary dynamics because it mediates the relative effects of selection. However, because most Ne estimates for unicellular organisms are derived either from taxa with poorly understood species boundaries or from host-restricted pathogens and most unicellular species have prominent phases of clonal propagation potentially subject to strong selective sweeps, the hypothesis that Ne is elevated in single-celled organisms remains controversial. Drawing from observations on well-defined species within the genus Paramecium, we report exceptionally high levels of silent-site polymorphism, which appear to be a reflection of large Ne. © The Author 2006. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved.