Qiao-Ping Xiang

Phylogeography of the Sino-Himalayan Fern Lepisorus clathratus on “The Roof of the World”

Background The Qinghai-Tibetan Plateau (QTP) and its southern and southeastern mountain ranges, Himalaya-Hengduan Mountains (HHM), are one of the most extensive habitats for alpine plants in the world. How ferns occurring in QTP and HHM changed their distribution ranges in response to Quaternary climatic oscillations remains almost unknown. Methodology and Results We employed sequences of two chloroplast DNA regions, rps4-trnS and trnL-trnF, to reconstruct phylogeography of the Sino-Himalayan fern Lepisorus clathratus, occurring mainly in the QTP and HHM. Individuals of this species have either dehiscent or indehiscent sporangia with the latter evolved from the plesiomorphic dehiscent forms. Based on a range-wide sampling, we detected 27 cpDNA haplotypes that were divided into five groups by network analyses. Populations in the Hengduan Mountains possess the highest genetic diversity, while a single haplogroup is detected across the north-central region. A distinct phylogeographical subdivision was detected between the Hengduan Mountains and north-central region by AMOVA analysis. The haplogroup distribution pattern, coalescence and AMOVA analysis suggest that a long term survival area (refugia) of the species was located in the Hengduan Mountains during glaciations, with probable range expansions into north-central regions during interglacial periods. Populations with indehiscent sporangium can carry private haplotypes and are inclined to maintain genetic homogeneity. One group with indehiscent sporangia most likely survived in situ on the QTP during glaciations. Conclusions/Significance This study for the first time sheds light on the response of alpine ferns in the QTP and HHM to the Quaternary climatic oscillations.

The rise of the Himalaya enforced the diversification of SE Asian ferns by altering the monsoon regimes

BackgroundThe rise of high mountain chains is widely seen as one of the factors driving rapid diversification of land plants and the formation of biodiversity hotspots. Supporting evidence was reported for the impact of the rapid rise of the Andean mountains but this hypothesis has so far been less explored for the impact of the “roof of the world”. The formation of the Himalaya, and especially the rise of the Qinghai–Tibetan Plateau in the recent 20 million years, altered the monsoon regimes that dominate the current climates of South East Asia. Here, we infer the hypothesis that the rise of Himalaya had a strong impact on the plant diversity in the biodiversity hotspot of the Southwest Chinese Mountains.ResultsOur analyses of the diversification pattern of the derived fern genus Lepisorus recovered evidence for changes in plant diversity that correlated with the strengthening of South East Asian monsoon. Southwest China or Southwest China and Japan was recovered as the putative area of origin of Lepisorus and enhancing monsoon regime were found to shape the early diversification of the genus as well as subsequent radiations during the late Miocene and Pliocene.ConclusionsWe report new evidence for a coincidence of plant diversification and changes of the climate caused by the uplift of the Himalaya. These results are discussed in the context of the impact of incomplete taxon sampling, uncertainty of divergence time estimates, and limitations of current methods used to assess diversification rates.

Phylogeny of the paleotropical fern genus Lepisorus (Polypodiaceae, Polypodiopsida) inferred from four chloroplast DNA regions

Phylogenetic relationships within the paleotropical genus Lepisorus (Polypodiaceae) were investigated using plastid DNA sequences from four regions: rbcL, rps4 and rps4-trnS IGS, trnL intron plus trnL-F IGS, rbcL-atpB IGS. Over 4000 nucleotides were sequenced for 77 specimens belonging to 54 species. Each cpDNA region was analyzed separately and combined into a single dataset. All phylogenetic analyses, maximum parsimony, maximum likelihood and Bayesian Inference of phylogeny, revealed the paraphyly of Lepisorus with the monotypic Drymotaenium miyoshianum and of the paleotropical genus Belvisia nested within the Lepisorus clade. Nine well-supported major clades were found. The phylogenetic results provided new evidence for the sectional classification of Lepisorus. The evolution of three morphological characters, clathrateness of rhizome scales, margin of rhizome scales and defoliated leaves, and the evolution of the karyotype, were reconstructed to identify lineage specific phenotypic character states or combination of characters. Unique character combinations, rather than synapomorphies, were found to be of systematic value in sectional delimitation. The variation of chromosome numbers is largely due to a single aneuploidy event instead of a stepwise reduction during the evolutionary history of this genus.

Indehiscent sporangia enable the accumulation of local fern diversity at the Qinghai-Tibetan Plateau.

BackgroundIndehiscent sporangia are reported for only a few of derived leptosporangiate ferns. Their evolution has been likely caused by conditions in which promotion of self-fertilization is an evolutionary advantageous strategy such as the colonization of isolated regions and responds to stressful habitat conditions. The Lepisorus clathratus complex provides the opportunity to test this hypothesis because these derived ferns include specimens with regular dehiscent and irregular indehiscent sporangia. The latter occurs preferably in well-defined regions in the Himalaya. Previous studies have shown evidence for multiple origins of indehiscent sporangia and the persistence of populations with indehiscent sporangia at extreme altitudinal ranges of the Qinghai-Tibetan Plateau (QTP).ResultsIndependent phylogenetic relationships reconstructed using DNA sequences of the uniparentally inherited chloroplast genome and two low-copy nuclear genes confirmed the hypothesis of multiple origins of indehiscent sporangia and the restriction of particular haplotypes to indehiscent sporangia populations in the Lhasa and Nyingchi regions of the QTP. In contrast, the Hengduan Mountains were characterized by high haplotype diversity and the occurrence of accessions with and without indehiscent sporangia. Evidence was found for polyploidy and reticulate evolution in this complex. The putative case of chloroplast capture in the Nyingchi populations provided further evidence for the promotion of isolated but persistent populations by indehiscent sporangia.ConclusionsThe presented results confirmed the hypothesis that indehiscent sporangia promote the establishment of persistent population in different regions of the QTP. These results are consistent with the expectations of reproductive reassurance by promotion of self-fertilization that played a critical role in the assembly of populations in isolated locations and/or extreme habitats.

Plastid Phylogenomics Resolve Deep Relationships among Eupolypod II Ferns with Rapid Radiation and Rate Heterogeneity

Abstract The eupolypods II ferns represent a classic case of evolutionary radiation and, simultaneously, exhibit high substitution rate heterogeneity. These factors have been proposed to contribute to the contentious resolutions among clades within this fern group in multilocus phylogenetic studies. We investigated the deep phylogenetic relationships of eupolypod II ferns by sampling all major families and using 40 plastid genomes, or plastomes, of which 33 were newly sequenced with next-generation sequencing technology. We performed model-based analyses to evaluate the diversity of molecular evolutionary rates for these ferns. Our plastome data, with more than 26,000 informative characters, yielded good resolution for deep relationships within eupolypods II and unambiguously clarified the position of Rhachidosoraceae and the monophyly of Athyriaceae. Results of rate heterogeneity analysis revealed approximately 33 significant rate shifts in eupolypod II ferns, with the most heterogeneous rates (both accelerations and decelerations) occurring in two phylogenetically difficult lineages, that is, the Rhachidosoraceae–Aspleniaceae and Athyriaceae clades. These observations support the hypothesis that rate heterogeneity has previously constrained the deep phylogenetic resolution in eupolypods II. According to the plastome data, we propose that 14 chloroplast markers are particularly phylogenetically informative for eupolypods II both at the familial and generic levels. Our study demonstrates the power of a character-rich plastome data set and high-throughput sequencing for resolving the recalcitrant lineages, which have undergone rapid evolutionary radiation and dramatic changes in substitution rates.

A new species of Keteleeria (Pinaceae) in the Shanwang Miocene flora of China and its phytogeographic connection with North America

The presence of Keteleeria in the Miocene of eastern China is confirmed by the discovery of a cone, winged seeds, and leafy shoots. These are described and compared with other fossil and recent representatives. The best match was with K. rujadana, a K. fortunei-like fossil from the Oligocene of Oregon, U.S.A. The presence of similar, if not identical taxa, on both sides of the Pacific indicates that in the Mid-Tertiary exchange between East Asia and North America via the Beringian land-bridge was still possible. With global cooling in the Tertiary, this thermophilic conifer became scarce. Its present restricted distribution dates from the Quaternary.

Molecular Phylogeny of the Cliff Ferns (Woodsiaceae: Polypodiales) with a Proposed Infrageneric Classification

The cliff fern family Woodsiaceae has experienced frequent taxonomic changes at the familial and generic ranks since its establishment. The bulk of its species were placed in Woodsia, while Cheilanthopsis, Hymenocystis, Physematium, and Protowoodsia are segregates recognized by some authors. Phylogenetic relationships among the genera of Woodsiaceae remain unclear because of the extreme morphological diversity and inadequate taxon sampling in phylogenetic studies to date. In this study, we carry out comprehensive phylogenetic analyses of Woodsiaceae using molecular evidence from four chloroplast DNA markers (atpA, matK, rbcL and trnL–F) and covering over half the currently recognized species. Our results show three main clades in Woodsiaceae corresponding to Physematium (clade I), Cheilanthopsis–Protowoodsia (clade II) and Woodsia s.s. (clade III). In the interest of preserving monophyly and taxonomic stability, a broadly defined Woodsia including the other segregates is proposed, which is characterized by the distinctive indument and inferior indusia. Therefore, we present a new subgeneric classification of the redefined Woodsia based on phylogenetic and ancestral state reconstructions to better reflect the morphological variation, geographic distribution pattern, and evolutionary history of the genus. Our analyses of the cytological character evolution support multiple aneuploidy events that have resulted in the reduction of chromosome base number from 41 to 33, 37, 38, 39 and 40 during the evolutionary history of the cliff ferns.

New infrageneric classification of Abies in light of molecular phylogeny and high diversity in western North America: New infrageneric classification of Abies

Abies Mill. represents one of the most diverse lineages in Pinaceae with ca. 50 species. Recent phylogenetic studies of Abies using regions of the nuclear and plastid genomes generally support recent classifications. However, we have previously shown that in several cases sectional memberships should be revised, and more species are needed to generate a robust infrageneric classification. Therefore, we present a revision of Abies taxonomy based on phylogeny using the most comprehensive taxon sampling (52 taxa worldwide) to date and five chloroplast gene regions and one single‐copy nuclear gene (LFY). Our phylogenetic analyses, including maximum parsimony, maximum likelihood, and Bayesian inference, yield seven well‐supported lineages that are consistent with previous studies. Our taxonomic revision integrates the phylogenies presented here as well as those from other studies. We merged sect. Pseudopicea with sect. Momi, recognized the merger of sect. Abies with sect. Piceaster, and sect. Grandis with sect. Oiamel. We recognized sect. Balsamea by excluding A. kawakamii (Hayata) T. Itô and we suspect that ancient hybridization was involved in its origin. A short morphological description is provided for each section, as well as its geographic distribution and list of accepted names of species. Five of the seven sections consist primarily of species in western North America, especially within the California Floristic Province. Phylogenetic results show that western North America is home to an exceptionally high diversity of fir lineages, which is further corroborated by the cuticle morphology and internal transcribed spacer genotypes based on the length differences.

Elevation Shift in Abies Mill. (Pinaceae) of Subtropical and Temperate China and Vietnam—Corroborative Evidence from Cytoplasmic DNA and Ecological Niche Modeling

The “elevational shift” scenario has been proposed as a model to explain the response of cold-adapted organisms to Quaternary climatic fluctuations in Europe and North America. However, the elevational shift model has not been well-explored in eastern Asia, which is more topographically complex than the other Northern Hemisphere biogeographic regions. Here, we evaluated the role of elevational shift in the closely related firs, or Abies Mill., of subtropical and temperate China. These firs are typical alpine trees with sensitivity to climate change. We tested the elevational shift hypothesis in firs of China using phylogeographic methods and ecological niche models. Our phylogeographic analyses comprised mitochondrial and chloroplast polymorphisms surveyed across 479 individuals from 43 populations representing 11 species. M1 of the 11 mitotypes and C1 of the 25 chlorotypes were inferred as the ancestral haplotype, and they had the widest distribution. The results of our phylogeographic survey revealed multiple centers of genetic diversity in distinct geographic regions and no latitudinal trend. Moreover, our results showed range expansions for seven taxa during the last glacial (64.9–18.2 or 32.5–9.1 kya), and this was consistent with the Quaternary fossil record of Abies in China. Taken together, our findings support a historical biogeographic pattern in firs of glacial expansions, probably through corridors at lower elevation, and interglacial fragmentations, through isolation at higher elevation peaks. Therefore, Abies in China probably undergoes elevational shift in response to climate change. Facing the forecasting global warming, the risk of several critically endangered firs was further enhanced as these species would have little escape space in situ to higher altitudes. According to our ENMs, we proposed an ex situ conservation strategy in the southern Hengduan Mountains region of south western China.