title: Differences in dehydration tolerance among populations of a gametophyte-only fern.
abstract: OBJECTIVE
  For many plant species, historical climatic conditions may have left lasting imprints that are detectable in contemporary populations. Additionally, if these historical conditions also prevented gene flow among populations, these populations may be differentiated with respect to one another and their contemporary environmental conditions. For the fern,Vittaria appalachiana, one theory is that historical conditions during the Pleistocene largely shaped both the distribution and lack of sporophyte production. Our goals-based on this theory-were to examine physiological differences among and within populations spanning the species' geographic range, and the contribution of historical climatic conditions to this differentiation.
  
  
  METHODS
  We exposed explants from five populations to four drying treatments and examined differences in physiological response. Additionally, we examined the role of historical and current climatic conditions in driving the observed population differentiation.
  
  
  RESULTS
  Populations differ in their ability to tolerate varying levels of dehydration, displaying a pattern of countergradient selection. Exposure to historical and contemporary climatic conditions, specifically variation in temperature and precipitation regimes, resulted in population divergence observed among contemporary populations.
  
  
  CONCLUSIONS
  Historical conditions have shaped not only the distribution ofV. appalachiana, but also its current physiological limitations. Results from this study support the hypothesis that climatic conditions during the Pleistocene are responsible for the distribution of this species, and may be responsible for the observed differences in dehydration tolerance. Additionally, dehydration tolerance may be the driving factor for previously reported patterns of countergradient selection in this species.
authors.affiliation: University of Florida, Department of Biology, Gainesville, Florida, USA smstev2@ufl.edu.
authors.forename: Sally M
authors.initials: SM
authors.lastname: Chambers
authors.affiliation: Colgate University, Department of Biology, Hamilton, New York, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Watkins
authors.affiliation: University of Florida, Department of Biology, Gainesville, Florida, USA.
authors.forename: Emily B
authors.initials: EB
authors.lastname: Sessa
mesh_terms: D003681:Dehydration / Q000503:physiopathology; D055993:Germ Cells, Plant / Q000502:physiology; D029625:Pteridaceae / Q000502:physiology*; D012098:Reproduction / Q000502:physiology
keywords: Pleistocene; Vittaria appalachiana; asexual; countergradient selection; latitudinal distribution; life cycle