title: Climate structures genetic variation across a species' elevation range: a test of range limits hypotheses.
abstract: Gene flow may influence the formation of species range limits, and yet little is known about the patterns of gene flow with respect to environmental gradients or proximity to range limits. With rapid environmental change, it is especially important to understand patterns of gene flow to inform conservation efforts. Here we investigate the species range of the selfing, annual plant, Mimulus laciniatus, in the California Sierra Nevada. We assessed genetic variation, gene flow, and population abundance across the entire elevation-based climate range. Contrary to expectations, within-population plant density increased towards both climate limits. Mean genetic diversity of edge populations was equivalent to central populations; however, all edge populations exhibited less genetic diversity than neighbouring interior populations. Genetic differentiation was fairly consistent and moderate among all populations, and no directional signals of contemporary gene flow were detected between central and peripheral elevations. Elevation-driven gene flow (isolation by environment), but not isolation by distance, was found across the species range. These findings were the same towards high- and low-elevation range limits and were inconsistent with two common centre-edge hypotheses invoked for the formation of species range limits: (i) decreasing habitat quality and population size; (ii) swamping gene flow from large, central populations. This pattern demonstrates that climate, but not centre-edge dynamics, is an important range-wide factor structuring M. laciniatus populations. To our knowledge, this is the first empirical study to relate environmental patterns of gene flow to range limits hypotheses. Similar investigations across a wide variety of taxa and life histories are needed.
authors.affiliation: School of Natural Sciences, University of California, 5200 North Lake Rd., Merced, CA, 95343, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Sexton
authors.affiliation: Department of Ecology, Evolution and Organismal Biology, Iowa State University, 339A Bessey Hall, Ames, IA, 50011, USA.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Hufford
authors.affiliation: Department of Biology, Institute of Ecology and Evolution, University of Oregon, 77 Klamath Hall, 1210, Eugene, OR, 97403, USA.
authors.forename: Ashley C
authors.initials: AC
authors.lastname: Bateman
authors.affiliation: Department of Plant Biology, Michigan State University, 612 Wilson Road, East Lansing, MI, 48824, USA.
authors.forename: David B
authors.initials: DB
authors.lastname: Lowry
authors.affiliation: Institute of Integrative Nature Conservation Research, University of Natural Resources and Life Sciences (Boku), Gregor Mendel-Str. 33, 1180, Vienna, Austria.
authors.forename: Harald
authors.initials: H
authors.lastname: Meimberg
authors.affiliation: Department of Evolution and Ecology, University of California, One Shields Ave., Davis, CA, 95616, USA.
authors.forename: Sharon Y
authors.initials: SY
authors.lastname: Strauss
authors.affiliation: Department of Plant Sciences, University of California, One Shields Ave., Davis, CA, 95616, USA.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Rice
mesh_terms: D002140:California; D002980:Climate; D018744:DNA, Plant / Q000235:genetics; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D032241:Mimulus / Q000235:genetics*; D008957:Models, Genetic; D011156:Population Density; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant
keywords: Mimulus; elevation gradients; gene flow; isolation by environment; species range limits; swamping gene flow