title: Genetic introgression and species boundary of two geographically overlapping pine species revealed by molecular markers.
abstract: Gene introgression and hybrid barriers have long been a major focus of studies of geographically overlapping species. Two pine species, Pinus massoniana and P. hwangshanensis, are frequently observed growing adjacent to each other, where they overlap in a narrow hybrid zone. As a consequence, these species constitute an ideal system for studying genetic introgression and reproductive barriers between naturally hybridizing, adjacently distributed species. In this study, we sampled 270 pine trees along an elevation gradient in Anhui Province, China and analyzed these samples using EST-SSR markers. The molecular data revealed that direct gene flow between the two species was fairly low, and that the majority of gene introgression was intermediated by backcrossing. On the basis of empirical observation, the on-site distribution of pines was divided into a P. massoniana zone, a hybrid zone, and a P. hwangshanensis zone. STRUCTURE analysis revealed the existence of a distinct species boundary between the two pine species. The genetic boundary of the hybrid zone, on the other hand, was indistinct owing to intensive backcrossing with parental species. Compared with P. massoniana, P. hwangshanensis was found to backcross with the hybrids more intensively, consistent with the observation that morphological and anatomical characteristics of trees in the contact zone were biased towards P. hwangshanensis. The introgression ability of amplified alleles varied across species, with some being completely blocked from interspecific introgression. Our study has provided a living example to help explain the persistence of adjacently distributed species coexisting with their interfertile hybrids.
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Defang
authors: D
authors: Zhang
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Tao
authors: T
authors: Xia
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Maomao
authors: M
authors: Yan
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Xiaogang
authors: X
authors: Dai
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Jin
authors: J
authors: Xu
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Shuxian
authors: S
authors: Li
authors: The Southern Modern Forestry Collaborative Innovation Center, Nanjing Forestry University, Nanjing, China.
authors: Tongming
authors: T
authors: Yin
mesh_terms: D000531:Altitude; D001499:Bayes Theorem; D002681:China; D017931:DNA Primers / Q000378:metabolism; D020224:Expressed Sequence Tags; D005787:Gene Frequency / Q000235:genetics; D005788:Gene Pool; D005819:Genetic Markers; D014644:Genetic Variation; D005843:Geography; D018895:Microsatellite Repeats / Q000235:genetics; D028223:Pinus / Q000235:genetics*; D013045:Species Specificity
chemical_list: D017931:DNA Primers; D005819:Genetic Markers