title: Exploring species limits in two closely related Chinese oaks.
abstract: BACKGROUND
  The species status of two closely related Chinese oaks, Quercus liaotungensis and Q. mongolica, has been called into question. The objective of this study was to investigate the species status and to estimate the degree of introgression between the two taxa using different approaches.
  
  
  RESULTS
  Using SSR (simple sequence repeat) and AFLP (amplified fragment length polymorphism) markers, we found that interspecific genetic differentiation is significant and higher than the differentiation among populations within taxa. Bayesian clusters, principal coordinate analysis and population genetic distance trees all classified the oaks into two main groups consistent with the morphological differentiation of the two taxa rather than with geographic locations using both types of markers. Nevertheless, a few individuals in Northeast China and many individuals in North China have hybrid ancestry according to Bayesian assignment. One SSR locus and five AFLPs are significant outliers against neutral expectations in the interspecific FST simulation analysis, suggesting a role for divergent selection in differentiating species.
  
  
  CONCLUSIONS
  All results based on SSRS and AFLPS reached the same conclusion: Q. liaotungensis and Q. mongolica maintain distinct gene pools in most areas of sympatry. They should therefore be considered as discrete taxonomic units. Yet, the degree of introgression varies between the two species in different contact zones, which might be caused by different population history or by local environmental factors.
authors.affiliation: Key Laboratory of Silviculture of the State Forestry Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing, China.
authors.forename: Yan-Fei
authors.initials: YF
authors.lastname: Zeng
authors.forename: Wan-Jin
authors.initials: WJ
authors.lastname: Liao
authors.forename: Rémy J
authors.initials: RJ
authors.lastname: Petit
authors.forename: Da-Yong
authors.initials: DY
authors.lastname: Zhang
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D001499:Bayes Theorem; D002681:China; D016000:Cluster Analysis; D018744:DNA, Plant / Q000235:genetics*; D014644:Genetic Variation; D005838:Genotype; D005843:Geography; D018895:Microsatellite Repeats / Q000235:genetics*; D008957:Models, Genetic; D010802:Phylogeny; D029963:Quercus / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D013045:Species Specificity
chemical_list: D018744:DNA, Plant