Range expansion, genetic differentiation, and phenotypic adaption of Hippophaë neurocarpa (Elaeagnaceae) on the Qinghai–Tibet Plateau

Plant species shift ranges in response to climate fluctuation over time. However, differentiation related to heterogeneity in space has been illustrated only rarely. Here we selected Hippophaë neurocarpa S. W. Liu & T. N. Ho (Elaeagnaceae), a shrub endemic to the Qinghai–Tibet Plateau, to exemplify this process. We characterized the genotypic, phenotypic, and climatic variations among 27 populations of this species sampled across its entire distribution. Genotype analyses revealed six highly differentiated groups that may have resulted from expansions in spatial range. Despite recent fluctuation in size, it is likely that most groups survived the last glacial maximum in situ. Instead of two previously described subspecies, we identified four morphotypes (stellate, peltate, and two additional types) that can be characterized based on leaf trichomes. This phenotypic subdivision is consistent with a climate gradient defined by temperature and precipitation, although similar phenotypes may derive from distinct genotypes. Collectively, we propose that the demographic history of H. neurocarpa is characteristic of an early spatial range expansion combined with a recent bottleneck, subsequently subdivided into multiple morphotypes following local adaption to heterogeneous climates.