title: Weak crossability barrier but strong juvenile selection supports ecological speciation of the hybrid pine Pinus densata on the Tibetan plateau.
abstract: Determining how a new hybrid lineage can achieve reproductive isolation is a key to understanding the process and mechanisms of homoploid hybrid speciation. Here, we evaluated the degree and nature of reproductive isolation between the ecologically successful hybrid species Pinus densata and its parental species P. tabuliformis and P. yunnanensis. We performed interspecific crosses among the three species to assess their crossability. We then conducted reciprocal transplantation experiments to evaluate their fitness differentiation, and to examine how natural populations representing different directions of introgression differ in adaptation. The crossing experiments revealed weak genetic barriers among the species. The transplantation trials showed manifest evidence of local adaptation as the three species all performed best in their native habitats. Pinus densata populations from the western edge of its distribution have evolved a strong local adaptation to the specific habitat in that range; populations representing different directions of introgressants with the two parental species all showed fitness disadvantages in this P. densata habitat. These observations illustrate that premating isolation through selection against immigrants from other habitat types or postzygotic isolation through selection against backcrosses between the three species is strong. Thus, ecological selection in combination with endogenous components and geographic isolation has likely played a significant role in the speciation of P. densata.
authors: State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, Chinese Academy of Sciences, Beijing, 100093, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
authors: Wei
authors: W
authors: Zhao
authors: Jingxiang
authors: J
authors: Meng
authors: Baosheng
authors: B
authors: Wang
authors: Lisha
authors: L
authors: Zhang
authors: Yulan
authors: Y
authors: Xu
authors: Qing-Yin
authors: QY
authors: Zeng
authors: Yue
authors: Y
authors: Li
authors: Jian-Feng
authors: JF
authors: Mao
authors: Xiao-Ru
authors: XR
authors: Wang
mesh_terms: D049810:Genetic Speciation; D006824:Hybridization, Genetic; D028223:Pinus / Q000145:classification* / Q000235:genetics* / Q000502:physiology; D060047:Reproductive Isolation
keywords: Cross-compatibility; ecological selection; hybrid speciation; local adaptation; population divergence; transplantation experiment