title: Limited genetic divergence among Australian alpine Poa tussock grasses coupled with regional structuring points to ongoing gene flow and taxonomic challenges.
abstract: OBJECTIVE
  While molecular approaches can often accurately reconstruct species relationships, taxa that are incompletely differentiated pose a challenge even with extensive data. Such taxa are functionally differentiated, but may be genetically differentiated only at small and/or patchy regions of the genome. This issue is considered here in Poa tussock grass species that dominate grassland and herbfields in the Australian alpine zone.
  
  
  METHODS
  Previously reported tetraploidy was confirmed in all species by sequencing seven nuclear regions and five microsatellite markers. A Bayesian approach was used to co-estimate nuclear and chloroplast gene trees with an overall dated species tree. The resulting species tree was used to examine species structure and recent hybridization, and intertaxon fertility was tested by experimental crosses.
  
  
  RESULTS
  Species tree estimation revealed Poa gunnii, a Tasmanian endemic species, as sister to the rest of the Australian alpine Poa. The taxa have radiated in the last 0·5-1·2 million years and the non-gunnii taxa are not supported as genetically distinct. Recent hybridization following past species divergence was also not supported. Ongoing gene flow is suggested, with some broad-scale geographic structure within the group.
  
  
  CONCLUSIONS
  The Australian alpine Poa species are not genetically distinct despite being distinguishable phenotypically, suggesting recent adaptive divergence with ongoing intertaxon gene flow. This highlights challenges in using conventional molecular taxonomy to infer species relationships in recent, rapid radiations.
authors.affiliation: Department of Genetics, University of Melbourne, Parkville 3010, Victoria, Australia.
authors.forename: Philippa C
authors.initials: PC
authors.lastname: Griffin
authors.forename: Ary A
authors.initials: AA
authors.lastname: Hoffmann
mesh_terms: D001315:Australia; D051456:Gene Flow; D017343:Genes, Plant; D018895:Microsatellite Repeats / Q000235:genetics; D031785:Poa / Q000145:classification / Q000235:genetics*; D013045:Species Specificity
keywords: Poa; Species tree; alpine; divergence; gene flow; hybridization; polyploid; radiation; tussock grass