title: Genes mirror geography in Daphnia magna.
abstract: Identifying the presence and magnitude of population genetic structure remains a major consideration in evolutionary biology as doing so allows one to understand the demographic history of a species as well as make predictions of how the evolutionary process will proceed. Next-generation sequencing methods allow us to reconsider previous ideas and conclusions concerning the distribution of genetic variation, and what this distribution implies about a given species evolutionary history. A previous phylogeographic study of the crustacean Daphnia magna suggested that, despite strong genetic differentiation among populations at a local scale, the species shows only moderate genetic structure across its European range, with a spatially patchy occurrence of individual lineages. We apply RAD sequencing to a sample of D. magna collected across a wide swath of the species' Eurasian range and analyse the data using principle component analysis (PCA) of genetic variation and Procrustes analytical approaches, to quantify spatial genetic structure. We find remarkable consistency between the first two PCA axes and the geographic coordinates of individual sampling points, suggesting that, on a continent-wide scale, genetic differentiation is driven to a large extent by geographic distance. The observed pattern is consistent with unimpeded (i.e. no barriers, landscape or otherwise) migration at large spatial scales, despite the fragmented and patchy nature of favourable habitats at local scales. With high-resolution genetic data similar patterns may be uncovered for other species with wide geographic distributions, allowing an increased understanding of how genetic drift and selection have shaped their evolutionary history.
authors.affiliation: Zoological Institute, University of Basel, Vesalgasse 1, Basel, CH-4051, Switzerland.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Fields
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive - UMR 5175, campus CNRS, 1919, route de Mende, 34293, Montpellier Cedex 5, France.|Department of Biology, Ecology and Evolution, University of Fribourg, Chemin du Muśee 10, 1700, Fribourg, Switzerland.
authors.forename: Céline
authors.initials: C
authors.lastname: Reisser
authors.affiliation: Zoological Institute, University of Basel, Vesalgasse 1, Basel, CH-4051, Switzerland.
authors.forename: Marinela
authors.initials: M
authors.lastname: Dukić
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive - UMR 5175, campus CNRS, 1919, route de Mende, 34293, Montpellier Cedex 5, France.|Department of Biology, Ecology and Evolution, University of Fribourg, Chemin du Muśee 10, 1700, Fribourg, Switzerland.
authors.forename: Christoph R
authors.initials: CR
authors.lastname: Haag
authors.affiliation: Zoological Institute, University of Basel, Vesalgasse 1, Basel, CH-4051, Switzerland.
authors.forename: Dieter
authors.initials: D
authors.lastname: Ebert
mesh_terms: D000818:Animals; D002874:Chromosome Mapping; D003621:Daphnia / Q000235:genetics*; D005060:Europe; D005260:Female; D015723:Gene Library; D005828:Genetics, Population; D005838:Genotype; D005843:Geography; D020641:Polymorphism, Single Nucleotide; D025341:Principal Component Analysis; D017422:Sequence Analysis, DNA
keywords: Daphnia magna; Procrustes analysis; isolation by distance; population genetic structure; principle component analysis