title: Evolutionary diversification and geographical isolation in Dubautia laxa (Asteraceae), a widespread member of the Hawaiian silversword alliance.
abstract: OBJECTIVE
  The Hawaiian silversword alliance (Asteraceae) is one the best examples of a plant adaptive radiation, exhibiting extensive morphological and ecological diversity. No research within this group has addressed the role of geographical isolation, independent of ecological adaptation, in contributing to taxonomic diversity. The aims of this study were to examine genetic differentiation among subspecies of Dubautia laxa (Asteraceae) to determine if allopatric or sympatric populations and subspecies form distinct genetic clusters to understand better the role of geography in diversification within the alliance.
  
  
  METHODS
  Dubautia laxa is a widespread member of the Hawaiian silversword alliance, occurring on four of the five major islands of the Hawaiian archipelago, with four subspecies recognized on the basis of morphological, ecological and geographical variation. Nuclear microsatellites and plastid DNA sequence data were examined. Data were analysed using maximum-likelihood and Bayesian phylogenetic methodologies to identify unique evolutionary lineages.
  
  
  RESULTS
  Plastid DNA sequence data resolved two highly divergent lineages, recognized as the Laxa and Hirsuta groups, that are more similar to other members of the Hawaiian silversword alliance than they are to each other. The Laxa group is basal to the young island species of Dubautia, whereas the Hirsuta group forms a clade with the old island lineages of Dubautia and with Argyroxiphium. The divergence between the plastid groups is supported by Bayesian microsatellite clustering analyses, but the degree of nuclear differentiation is not as great. Clear genetic differentiation is only observed between allopatric populations, both within and among islands.
  
  
  CONCLUSIONS
  These results indicate that geographical separation has aided diversification in D. laxa, whereas ecologically associated morphological differences are not associated with neutral genetic differentiation. This suggests that, despite the stunning ecological adaptation observed, geography has also played an important role in the Hawaiian silversword alliance plant adaptive radiation.
authors.affiliation: Rancho Santa Ana Botanic Garden, 1500 N. College Ave., Claremont, CA 91711, USA. mitchell.mcglaughlin@unco.edu
authors.forename: Mitchell E
authors.initials: ME
authors.lastname: McGlaughlin
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Friar
mesh_terms: D000220:Adaptation, Biological; D000595:Amino Acid Sequence; D019659:Asteraceae / Q000145:classification* / Q000235:genetics* / Q000502:physiology; D001483:Base Sequence; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D016000:Cluster Analysis; D018744:DNA, Plant / Q000235:genetics*; D019143:Evolution, Molecular; D006254:Hawaii; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D010802:Phylogeny; D058974:Phylogeography; D010940:Plant Proteins / Q000235:genetics; D018087:Plastids / Q000235:genetics; D016133:Polymerase Chain Reaction
chemical_list: D018744:DNA, Plant; D010940:Plant Proteins