title: North-South Colonization Associated with Local Adaptation of the Wild Tomato Species Solanum chilense.
abstract: After colonization population sizes may vary across the species range depending on environmental conditions and following colonizations. An interesting question is whether local adaptation occurs more frequently in large ancestral populations or in small derived populations. A higher number of new mutations and a lower effect of genetic drift should favor selection in large populations, whereas small derived populations may require an initial local adaptation event to facilitate the colonization of new habitats. Wild tomatoes are native to a broad range of different habitats characterized by variable abiotic conditions in South America, and represent an ideal system to study this interplay between demography and natural selection. Population genetic analyses and statistical inference of past demography were conducted on pooled-sequencing data from 30 genes (8,080 single nucleotide polymorphisms) from an extensive sampling of 23 Solanum chilense populations over Chile and Peru. We reveal first a north-south colonization associated with relaxed purifying selection in the south as shown by a decrease of genetic variation and an increasing proportion of nonsynonymous polymorphism from north to south, and population substructure with at least four genetic groups. Second, we uncover a dual picture of adaptation consisting of 1) a decreasing proportion of adaptive amino acid substitutions from north to south suggesting that adaptation is favored in large populations, whereas 2) signatures of local adaptation predominantly occur in the smaller populations from the marginal ranges in the south.
authors.affiliation: Section of Evolutionary Biology, Department of Biology II, Ludwig-Maximilians University of Munich, Planegg-Martinsried, Germany boendel@bio.lmu.de tellier@wzw.tum.de.
authors.forename: Katharina B
authors.initials: KB
authors.lastname: Böndel
authors.affiliation: Section of Evolutionary Biology, Department of Biology II, Ludwig-Maximilians University of Munich, Planegg-Martinsried, Germany.
authors.forename: Hilde
authors.initials: H
authors.lastname: Lainer
authors.affiliation: Section of Evolutionary Biology, Department of Biology II, Ludwig-Maximilians University of Munich, Planegg-Martinsried, Germany.
authors.forename: Tetyana
authors.initials: T
authors.lastname: Nosenko
authors.affiliation: DuPont de Nemours, European Research & Development Center for Crop Protection, Nambsheim, France.
authors.forename: Mamadou
authors.initials: M
authors.lastname: Mboup
authors.affiliation: Section of Population Genetics, Center of Life and Food Sciences Weihenstephan, Technische Universität München, Freising, Germany boendel@bio.lmu.de tellier@wzw.tum.de.
authors.forename: Aurélien
authors.initials: A
authors.lastname: Tellier
authors.affiliation: Section of Evolutionary Biology, Department of Biology II, Ludwig-Maximilians University of Munich, Planegg-Martinsried, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Stephan
mesh_terms: D000064:Acclimatization / Q000235:genetics*; D000222:Adaptation, Physiological / Q000235:genetics; D017753:Ecosystem; D019143:Evolution, Molecular; D014644:Genetic Variation; D005828:Genetics, Population; D018745:Genome, Plant; D011110:Polymorphism, Genetic; D011156:Population Density; D012641:Selection, Genetic / Q000235:genetics; D017422:Sequence Analysis, DNA; D032322:Solanum / Q000235:genetics* / Q000254:growth & development*; D013020:South America
keywords: demography; local adaptation; plant population genetics; positive selection; wild tomato