BackgroundThe family Brassicaceae encompasses diverse species, many of which have high scientific and economic importance. Early diversifications and phylogenetic relationships between major lineages or clades remain unclear. Here we re-investigate Brassicaceae phylogeny with complete plastomes from 51 species representing all four lineages or 5 of 6 major clades (A, B, C, E and F) as identified in earlier studies.ResultsBayesian and maximum likelihood phylogenetic analyses using a partitioned supermatrix of 77 protein coding genes resulted in nearly identical tree topologies exemplified by highly supported relationships between clades. All four lineages were well identified and interrelationships between them were resolved. The previously defined Clade C was found to be paraphyletic (the genus Megadenia formed a separate lineage), while the remaining clades were monophyletic. Clade E (lineage III) was sister to clades B + C rather than to all core Brassicaceae (clades A + B + C or lineages I + II), as suggested by a previous transcriptome study. Molecular dating based on plastome phylogeny supported the origin of major lineages or clades between late Oligocene and early Miocene, and the following radiative diversification across the family took place within a short timescale. In addition, gene losses in the plastomes occurred multiple times during the evolutionary diversification of the family.ConclusionsPlastome phylogeny illustrates the early diversification of cruciferous species. This phylogeny will facilitate our further understanding of evolution and adaptation of numerous species in the model family Brassicaceae.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-017-3555-3) contains supplementary material, which is available to authorized users.

Aim Hotspots of biodiversity are often associated with areas that have undergone orogenic activity during recent geological history. Mountain uplifts are known to catalyse species radiation but their impact on evolutionarily stable taxa such as many trees remains little understood. The oak Quercus aquifolioides is endemic to yet widely distributed across the Hengduanshan Biodiversity Hotspot in the Eastern Himalayas. Here, we investigate how the region's Neogene and Quaternary history has driven the species' past population dynamics and the resulting extant patterns of intraspecific diversity.Location Hengduanshan Biodiversity Hotspot in SW China.Methods We sampled 58 populations throughout the species range and genotyped a total of 959 individuals at four chloroplast DNA fragments and 11 nuclear microsatellite loci. Phylogenetic reconstructions, molecular dating techniques and ancestral area reconstructions were used in combination with population genetic statistics to infer the biogeographical history of Q. aquifolioides. The phylogeographical study was complemented by a survey of fossil records and a niche modelling exercise.Results Combined molecular and fossil evidence indicates that Q. aquifolioides descended during the late Miocene from the central Qinghai-Tibet Plateau into Tibet and the western Sichuan Plateau, and from there, into the area of highest endemism in the Hengduan Mountains sensu lato. Great apparent population stability and a haplotype 'radiation' in this area contrasted with marked extinction-recolonization dynamics and reduced population diversity in Tibet. We found evidence for extremely limited seed gene flow but extensive pollen gene flow (global F ST : cpDNA = 0.98, nSSR = 0.07) with signals of asymmetric pollen dispersal from the Hengduan Mountains into Tibet. Main conclusionOur results provide insights of unprecedented detail into the ancient biogeographical history of the Hengduanshan Biodiversity Hotspot, suggesting that past environmental changes in the region may have catalysed radiative diversifications within species much in the same way as among species.

The Qinghai–Tibet Plateau (QTP) sensu lato (sl) houses an exceptional species diversity in Asia. To develop a comprehensive understanding of species diversity in this fascinating region, we reviewed recent progress from biogeographic, paleogeographic, paleontological and genomic research of both plants and animals in the QTPsl. Numerous studies have been conducted to examine whether the QTPsl uplift triggered the production of rich species diversity there, whether a Quaternary “unified ice sheet” eliminated plants and animals on the central plateau and how high‐altitude species developed the extreme environment adaptations. Major disputes arose about the first issue, mainly from different understanding of the QTP circumscriptions and related uplift, inaccurate dating of molecular phylogenetic trees, and non‐causal correlations between uplift and species diversification. The QTPsl uplift is spatially and temporally heterogeneous, and abundant fossils reported recently similarly support such an asynchronous upheaval model across the entire region. Available phylogeographic studies of alpine plants and animals suggested their glacial refugia in the central QTPsl, rejecting a unified ice sheet during the Last Glacial Maximum. Genomic evidence from a limited number of alpine species has identified numerous candidate genes for high‐altitude adaptation. In the future, more studies should be focused on speciation and adaptation mechanisms of the alpine species in the QTPsl based on the cutting‐edge methods.

Species delimitation in tree species is notoriously challenging due to shared polymorphisms among species. An integrative survey that considers multiple operational criteria is a possible solution, and we aimed to test it in a species complex of aspens in China. Genetic [four chloroplast DNA (cpDNA) fragments and 14 nuclear microsatellite loci (nSSR)] and morphological variations were collected for 76 populations and 53 populations, respectively, covering the major geographic distribution of the Populus davidiana-rotundifolia complex. Bayesian clustering, analysis of molecular variance (AMOVA), Principle Coordinate Analysis (PCoA), ecological niche modeling (ENM), and gene flow (migrants per generation), were employed to detect and test genetic clustering, morphological and habitat differentiation, and gene flow between/among putative species. The nSSR data and ENM suggested that there are two separately evolving meta-population lineages that correspond to P. davidiana (pd) and P. rotundifolia (pr). Furthermore, several lines of evidence supported a subdivision of P. davidiana into Northeastern (NEC) and Central-North (CNC) groups, yet they are still functioning as one species. CpDNA data revealed that five haplotype clades formed a pattern of [pdNEC, ((pdCNC, pr), (pdCNC, pr))], but most haplotypes are species-specific. Meanwhile, PCA based on morphology suggested a closer relationship between the CNC group (P. davidiana) and P. rontundifolia. Discrepancy of nSSR and ENM vs. cpDNA and morphology could have reflected a complex lineage divergence and convergence history. P. davidiana and P. rotundifolia can be regarded as a recently diverged species pair that experienced parapatric speciation due to ecological differentiation in the face of gene flow. Our findings highlight the importance of integrative surveys at population level, as we have undertaken, is an important approach to detect the boundary of a group of species that have experienced complex evolutionary history.

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