Distinct niche divergence characterizes the homoploid hybrid speciation of Pinus densata on the Tibetan Plateau

Ecological divergence and selection for novel adaptations to new habitats have been theoretically proposed to play important roles in promoting homoploid hybrid speciation (HHS). The successful establishment of Pinus densata on the Tibetan Plateau is one of the few known examples of HHS. In this study, we carried out extensive field expeditions to obtain representative coverage of occurrence sites of P. densata and its two putative parents. We then applied a series of GIS-based analyses to define the patterns of environmental variation within and among the three pine species, to remove potentially confounding effects of spatial autocorrelation in the environmental data due to allopatric ranges, and to build species distribution models. All results consistently indicated that the ecological preferences of P. densata and its parental species have diverged, and identified candidate ecological factors associated with habitat-specific adaptation. Projections from niche modelling indicated t...