title: Population differentiation and countergradient variation throughout the geographic range in the fern gametophyte Vittaria appalachiana.
abstract: OBJECTIVE
  Theory predicts that limited gene flow between populations will promote population differentiation, and experimental studies have found that differentiation is often explained by local adaptation in sexually reproducing angiosperms. However, few experiments have examined the drivers of differentiation among populations in asexual land plants with limited dispersal potential. Here, we evaluated the role of temperature in driving population differentiation in an asexual, obligate gametophyte fern species.
  
  
  METHODS
  We reciprocally transplanted Vittaria appalachiana gametophytes among six populations that spanned the species' geographic range in the Appalachian Mountains and Plateau. Temperature, survival, and senescence rates were measured for 1 year.
  
  
  RESULTS
  Populations had significantly different fitness responses to different sites, consistent with the hypothesis that populations have differentiated across the species' range. There was some evidence for local adaptation in marginal populations and for countergradient selection favoring particularly robust genotypes at the northern range edge. Most populations had relatively high fitness at the site with the most stable temperature conditions and were negatively affected by decreasing minimum temperatures.
  
  
  CONCLUSIONS
  Populations of Vittaria appalachiana exhibit highly variable responses to transplantation across the species' range, and only a small subset of these responses are due to local adaptation. Differences in daily minimum temperature explain some variation in fitness, but other site-specific factors also have significant impacts on transplant fitness. These results indicate that asexual, patchily distributed species with limited dispersal may exhibit population-specific responses to global climate change that have not been elucidated by empirical work focused on sexually reproducing angiosperms.
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana, USA, 47907.
authors.forename: Sally M
authors.initials: SM
authors.lastname: Chambers
authors.affiliation: Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana, USA, 47907 Department of Ecology and Evolutionary Biology, UCB 334, University of Colorado, Boulder, Colorado, 80309-0334 USA Nancy.Emery@Colorado.edu.
authors.forename: Nancy C
authors.initials: NC
authors.lastname: Emery
mesh_terms: D000220:Adaptation, Biological; D001061:Appalachian Region; D029624:Ferns / Q000235:genetics / Q000502:physiology*; D051456:Gene Flow; D055993:Germ Cells, Plant / Q000502:physiology*; D007196:Indiana; D063148:Plant Dispersal
keywords: Pteridaceae; Vittaria appalachiana; climate change; countergradient selection; gametophyte; geographic range; local adaptation; population differentiation; reciprocal transplant; temperature variation