title: Edaphic adaptation maintains the coexistence of two cryptic species on serpentine soils.
abstract: OBJECTIVE
  Divergent edaphic adaptation can contribute to reproductive isolation and coexistence between closely related species, yet we know little about how small-scale continuous edaphic gradients contribute to this phenomenon. We investigated edaphic adaptation between two cryptic species of California wildflower, Lasthenia californica and L. gracilis (Asteraceae), which grow in close parapatry on serpentine soil.
  
  
  METHODS
  We reciprocally transplanted both species into the center of each species' habitat and the transition zone between species. We quantified multiple components of fitness and used aster models to predict fitness based on environmental variables. We sampled soil across the ridge throughout the growing season to document edaphic changes through time. We sampled naturally germinating seedlings to determine whether there was dispersal into the adjacent habitat and to help pinpoint the timing of any selection against migrants.
  
  
  RESULTS
  We documented within-serpentine adaptation contributing to habitat isolation between close relatives. Both species were adapted to the edaphic conditions in their native region and suffered fitness trade-offs when moved outside that region. However, observed fitness values did not perfectly match those predicted by edaphic variables alone, indicating that other factors, such as competition, also contributed to plant fitness. Soil water content and concentrations of calcium, magnesium, sodium, and potassium were likely drivers of differential fitness. Plants either had limited dispersal ability or migrants experienced early-season mortality outside their native region.
  
  
  CONCLUSIONS
  Demonstrating that continuous habitats can support differently adapted, yet closely related, taxa is important to a broader understanding of how species are generated and maintained in nature.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA. jmyost@ucsc.edu
authors.forename: Jenn M
authors.initials: JM
authors.lastname: Yost
authors.forename: Teri
authors.initials: T
authors.lastname: Barry
authors.forename: Kathleen M
authors.initials: KM
authors.lastname: Kay
authors.forename: Nishanta
authors.initials: N
authors.lastname: Rajakaruna
mesh_terms: D000222:Adaptation, Physiological; D019659:Asteraceae / Q000502:physiology*; D002140:California; D019015:Geologic Sediments / Q000737:chemistry*; D008954:Models, Biological; D025341:Principal Component Analysis; D058614:Seed Dispersal; D012987:Soil / Q000737:chemistry*; D013997:Time Factors
chemical_list: D012987:Soil