title: Pure species in a continuum of genetic and morphological variation: sympatric oaks at the edge of their range.
abstract: OBJECTIVE
  Studies on oaks (Quercus spp.) have often been hampered by taxonomic confusion, a situation further compounded by the occurrence of extensive interspecific hybridization. In the present study, a combination of genetic and morphological analyses was used to examine sympatric populations of Q. petraea and Q. robur at the north-western edge of their ranges in Northern Ireland, since it had previously been suggested that hybridization could facilitate the apparent rapid, long-distance dispersal of oaks following the glaciations.
  
  
  METHODS
  Samples were collected from 24 sites across Northern Ireland that had been previously designated as ancient or semi-natural woodland. Genotypes were obtained from a total of 950 trees using 12 nuclear microsatellite loci, and admixture coefficients were calculated based on a Bayesian clustering approach. Individuals were also classified as Q. petraea,Q. robur or hybrids based on two objective morphometric characters shown previously to delineate pure individuals effectively. Genetically 'pure' individuals of both species, as defined by the Bayesian clustering, were also genotyped for five chloroplast microsatellites.
  
  
  RESULTS
  Genetic and morphological analyses both indicated the presence of pure individuals of both species, as well as a continuum of intermediates. There was a good agreement between the molecular and morphological classification, with a generally clear separation between pure individuals.
  
  
  CONCLUSIONS
  Despite millennia of hybridization and introgression, genetically and morphologically pure individuals of both Q. petraea and Q. robur can be found at the edge of their range, where both species occur sympatrically. The high proportion of individuals exhibiting introgression compared with previous studies may reflect the historical role of hybridization in facilitating dispersal following the glaciations. This is further supported by the significantly higher chloroplast diversity in Q. robur compared with Q. petraea.
authors.affiliation: School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK, Quercus, School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK and Institute for Global Food Security, Queen's University Belfast.
authors.forename: Gemma E
authors.initials: GE
authors.lastname: Beatty
authors.affiliation: School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK, Quercus, School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK and Institute for Global Food Security, Queen's University Belfast.
authors.forename: W Ian
authors.initials: WI
authors.lastname: Montgomery
authors.affiliation: School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK, Quercus, School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK and.
authors.forename: Florentine
authors.initials: F
authors.lastname: Spaans
authors.affiliation: School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK, Quercus, School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK and.
authors.forename: David G
authors.initials: DG
authors.lastname: Tosh
authors.affiliation: School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK, Quercus, School of Biological Sciences, Queen's University Belfast, 97 Lisburn Road, Belfast BT9 7BL, UK and Institute for Global Food Security, Queen's University Belfast J.Provan@qub.ac.uk.
authors.forename: Jim
authors.initials: J
authors.lastname: Provan
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D002736:Chloroplasts / Q000235:genetics; D014644:Genetic Variation; D005843:Geography; D029963:Quercus / Q000033:anatomy & histology* / Q000235:genetics*; D013045:Species Specificity; D061350:Sympatry / Q000235:genetics*
keywords: Hybridization; Quercus petraea; Quercus robur; introgression; microsatellites; morphological analysis; oak; species delineation