RT Journal Article SR Electronic T1 Sex and gene flow modulate evolution during range expansions in the protist Tetrahymena thermophila JF bioRxiv FD Cold Spring Harbor Laboratory SP 863340 DO 10.1101/863340 A1 Felix Moerman A1 Emanuel A. Fronhofer A1 Andreas Wagner A1 Florian Altermatt YR 2019 UL http://biorxiv.org/content/early/2019/12/03/863340.abstract AB At species’ range edges, individuals often face novel environmental conditions that may limit expansion until populations adapt. The potential to adapt depends on genetic variation upon which selection can act. However, populations at species’ range edges are often genetically depauperated. One mechanism to increase genetic variation is to reshuffle existing variation through sex. During range expansions, sex can, however, act as a double-edged sword. The gene swamping hypothesis predicts that for populations expanding along an abiotic gradient, sex can hinder adaptation if asymmetric dispersal leads to numerous maladapted dispersers from the range core swamping the range edge. In this study, we experimentally tested the gene swamping hypothesis by performing replicated range expansions in landscapes with or without an abiotic pH-gradient, using the ciliate Tetrahymena thermophila, while simultaneously manipulating the occurrence of gene flow and sex. We show that sex accelerated evolution of the intrinsic rate of increase in absence of gene flow, but hindered it in presence of gene flow. The effect of sex, however, was independent of the pH-gradient. Conversely, sex and gene flow did not affect expansion distance, possibly due to the discrete landscape structure. Overall, our results suggest that gene swamping can affect adaptation in life-history strategies.