Genetic divergence and phylogeographic history of two closely related species (Leucomeris decora and Nouelia insignis) across the 'Tanaka Line' in Southwest China

Across two phylogeographic breaks: Quaternary evolutionary history of a mountain aspen (Populus rotundifolia) in the Hengduan Mountains

Biogeographical barriers to gene flow are central to plant phylogeography. In East Asia, plant distribution is greatly influenced by two phylogeographic breaks, the Mekong-Salween Divide and Tanaka-Kaiyong Line, however, few studies have investigated how these barriers affect the genetic diversity of species that are distributed across both. Here we used 14 microsatellite loci and four chloroplast DNA fragments to examine genetic diversity and distribution patterns of 49 populations of Populus rotundifolia, a species that spans both the Mekong-Salween Divide and the Tanaka-Kaiyong Line in southwestern China. Demographic and migration hypotheses were tested using coalescent-based approaches. Limited historical gene flow was observed between the western and eastern groups of P. rotundifolia, but substantial flow occurred across both the Mekong-Salween Divide and Tanaka-Kaiyong Line, manifesting in clear admixture and high genetic diversity in the central group. Wind-borne pollen and seeds may have facilitated the dispersal of P. rotundifolia following prevalent northwest winds in the spring. We also found that the Hengduan Mountains, where multiple genetic barriers were detected, acted on the whole as a barrier between the western and eastern groups of P. rotundifolia. Ecological niche modeling suggested that P. rotundifolia has undergone range expansion since the last glacial maximum, and demographic reconstruction indicated an earlier population expansion around 600 Ka. The phylogeographic pattern of P. rotundifolia reflects the interplay of biological traits, wind patterns, barriers, niche differentiation, and Quaternary climate history. This study emphasizes the need for multiple lines of evidence in understanding the Quaternary evolution of plants in topographically complex areas.

Are 150 km of open sea enough? Gene flow and population differentiation in a bat-pollinated columnar cactus

Genetic differentiations and phylogeographical patterns are controlled by the interplay between spatial isolation and gene flow. To assess the extent of gene flow across an oceanic barrier, we explored the effect of the separation of the peninsula of Baja California on the evolution of mainland and peninsular populations of the long-lived columnar cactus Stenocereus thurberi. We analyzed twelve populations throughout the OPC distribution range to assess genetic diversity and structure using chloroplast DNA sequences. Genetic diversity was higher (Hd = 0.81), and genetic structure was lower (GST = 0.143) in mainland populations vs peninsular populations (Hd = 0.71, GST = 0.358 respectively). Genetic diversity was negatively associated with elevation but positively with rainfall. Two mainland and one peninsular ancestral haplotypes were reconstructed. Peninsular populations were as isolated among them as with mainland populations. Peninsular haplotypes formed a group with one mainland coastal population, and populations across the gulf shared common haplotypes giving support to regular gene flow across the Gulf. Gene flow is likely mediated by bats, the main pollinators and seed dispersers. Niche modeling suggests that during the Last Glacial Maximum (c. 130 ka), OPC populations shrank to southern locations. Currently, Stenocereus thurberi populations are expanding, and the species is under population divergence despite ongoing gene flow. Ancestral populations are located on the mainland and although vicariant peninsular populations cannot be ruled out, they are likely the result of gene flow across the seemingly formidable barrier of the Gulf of California. Still, unique haplotypes occur in the peninsula and the mainland, and peninsular populations are more structured than those on the mainland.

Wind-dispersed seeds blur phylogeographic breaks: The complex evolutionary history of Populus lasiocarpa around the Sichuan Basin

The strength of phylogeographic breaks can vary among species in the same area despite being subject to the same geological and climate history due to differences in biological traits. Several important phylogeographic breaks exist around the Sichuan Basin in Southwest China but few studies have focused on wind-dispersed plants. Here, we investigated the phylogeographic patterns and the evolutionary history of Populus lasiocarpa, a wind-pollinated and wind-dispersed tree species with a circum-Sichuan Basin distribution in southwest China. We sequenced and analyzed three plastid DNA fragments (ptDNA) and eight nuclear microsatellites (nSSRs) of 265 individuals of P. lasiocarpa from 21 populations spanning the entire distribution range. Distribution patterns based on nSSR data revealed that there are three genetic groups in P. lasiocarpa. This is consistent with the three phylogeographic breaks (Sichuan Basin, the Kaiyong Line and the 105°E line), where the Sichuan basin acts as the main barrier to gene flow between western and eastern groups. However, the distribution pattern based on ptDNA haplotypes poorly matched the phylogeographic breaks, and wind-dispersed seeds may be one of the main contributing factors. Species distribution modelling suggested a larger potential distribution in the last glacial maximum with a severe bottleneck during the last interglacial. A DIYABC model also suggested a population contraction and expansion for both western and eastern lineages. These results indicate that biological traits are likely to affect the evolutionary history of plants, and that nuclear molecular markers, which experience higher levels of gene flow, might be better indicators of phylogeographic breaks.

Genetic Diversity Study on Geographical Populations of the Multipurpose Species Elsholtzia stauntonii Using Transferable Microsatellite Markers

Elsholtzia stauntonii Benth. (Lamiaceae) is an economically important ornamental, medicinal and aromatic plant species. To meet the increasing market demand for E. stauntonii, it is necessary to assess genetic diversity within the species to accelerate the process of genetic improvement. Analysis of the transferability of simple sequence repeat (SSR) markers from related species or genera is a fast and economical method to evaluate diversity, and can ensure the availability of molecular markers in crops with limited genomic resources. In this study, the cross-genera transferability of 497 SSR markers selected from other members of the Lamiaceae (Salvia L., Perilla L., Mentha L., Hyptis Jacq., Leonurus L., Pogostemon Desf., Rosmarinus L., and Scutella L.) to E. stauntonii was 9.05% (45 primers). Among the 45 transferable markers, 10 markers revealed relatively high polymorphism in E. stauntonii. The genetic variation among 825 individuals from 18 natural populations of E. stauntonii in Hebei Province of China was analyzed using the 10 polymorphic SSR markers. On the basis of the SSR data, the average number of alleles (N _A), expected heterozygosity (H _E), and Shannon's information index (I) of the 10 primers pairs were 7.000, 0.478, and 0.688, respectively. Lower gene flow (N _m = 1.252) and high genetic differentiation (F _st = 0.181) were detected in the populations. Analysis of molecular variance (AMOVA) revealed that most of the variation (81.47%) was within the populations. Integrating the results of STRUCTURE, UPGMA (Unweighted Pair Group Method with Arithmetic Mean) clustering, and principal coordinate analysis, the 825 samples were grouped into two clusters associated with geographical provenance (southwestern and northeastern regions), which was consistent with the results of a Mantel test (r = 0.56, p < 0.001). Overall, SSR markers developed in related genera were effective to study the genetic structure and genetic diversity in geographical populations of E. stauntonii. The results provide a theoretical basis for conservation of genetic resources, genetic improvement, and construction of a core collection for E. stauntonii.

Determinants of Genetic Structure in a Highly Heterogeneous Landscape in Southwest China

Intra-specific genetic diversity is a fundamental component of biodiversity, and is key to species adaptation and persistence. However, significant knowledge gaps still exist in our understanding of the patterns of genetic diversity and their key determinants. Most previous investigations mainly utilized single-species and/or a limited number of explanatory variables; so here we mapped the patterns of plastid genetic diversity within 15 plant species, and explored the key determinants shaping these patterns using a wide range of variables. Population-level cpDNA sequence data for 15 plant species from the Longitudinal Range Gorge Region (LRGR), southwest China, were retrieved from literature and used to estimate haplotype diversity (H _D) and population pairwise genetic differentiation (F _ST) indices. Genetic diversity and divergence landscape surfaces were then generated based on the H _D and F _ST, respectively, to clarify the patterns of genetic structure in the region. Subsequently, we analyzed the relationships between plastid genetic diversity and 16 explanatory variables (classified as anthropogenic, climatic, and topographic). We found that the highest genetic diversity occurred in the Yulong Mountain region, with a significant proportion (~74.81%) of the high diversity land area being located outside of protected areas. The highest genetic divergence was observed approximately along the 25°N latitudinal line, with notable peaks in the western and eastern edges of the LRGR. Genetic diversity (H _D) was weakly but significantly positively correlated with both Latitude (lat) and Annual Mean Wet Day Frequency (wet), yet significantly negatively correlated with all of Longitude (long), Annual Mean Cloud Cover Percent (cld), Annual Mean Anthropogenic Flux (ahf), and Human Footprint Index (hfp). A combination of climatic, topographic, and anthropogenic factors explained a significant proportion (78%) of genetic variation, with topographic factors (lat and long) being the best predictors. Our analysis identified areas of high genetic diversity (genetic diversity "hotspots") and divergence in the region, and these should be prioritized for conservation. This study contributes to a better understanding of the features that shape the distribution of plastid genetic diversity in the LRGR and thus would inform conservation management efforts in this species-rich, but vulnerable region.

New ent-kaurane diterpenoid acids from Nouelia insignis Franch and their anti-inflammatory activity

Eleven undescribed ent-kaurane-type diterpenoid acids, namely noueinsiancins A–K (1–11), together with sixteen related known analogs (12–27) were isolated from Nouelia insignis Franch. The chemical structures and absolute configurations of the new compounds were confirmed by the extensive spectroscopic data, electronic circular dichroism (ECD) data analysis and single crystal X-ray diffraction. Additionally, the anti-inflammatory assay was applied to estimate the nitric oxide (NO) inhibitory activities of all compounds by using lipopolysaccharide (LPS)-induced RAW 264.7 cells in vitro. The results revealed that 4–7 and 13–17 significantly inhibited NO production at the concentrations of 2.5 μM, 5.0 μM and 10.0 μM. Meanwhile, compounds 6 and 7 were found to down-regulate the protein expression levels of IL-6 and TNF-α in RAW 264.7 cells induced by LPS in a dose-dependent manner. In conclusion, these findings provided the reference values for exploring the new chemicals with biological activities from this genus.

Eleven undescribed ent-kaurane-type diterpenoid acids, namely noueinsiancins A–K (1–11), together with sixteen related known analogs (12–27) were isolated from Nouelia insignis Franch.

Characterization of the complete chloroplast genome sequence of Chinese endemic species of Nouelia insignis (Hyalideae, Asteraceae) and its phylogenetic implications

This study was the first report complete chloroplast genome of Nouelia insignis (Asteraceae, Hyalideae), the large shrubs to small trees endemic to China. The circular whole cp genome of N. insignis was 151,524 bp in length, containing a large single-copy (LSC) region of 83,145 bp and a small single-copy (SSC) region of 18,261 bp. These two regions were separated by a pair of inverted repeat regions (IRa and IRb), each of them 25,060 bp in length. A total of 135 functional genes were encoded, consisting of 89 protein-coding genes, 38 tRNA genes, and eight rRNA genes. The overall GC content of the chloroplast genome sequence was 37.8%, and the GC contents of the LSC, SSC, and IR regions were 35.9, 31.5, and 43.2%, respectively. The phylogenetic analysis by the Bayesian analysis showed that the species of N.insignis was sister group with Gerbera jamesonii by strong support values, and thus was closely related to members of subfamilies of Cichorioideae and Pertyoideae. These results will be useful for the future studies of Asteraceae in the worldwide.

Population Evolution, Genetic Diversity and Structure of the Medicinal Legume, Glycyrrhiza uralensis and the Effects of Geographical Distribution on Leaves Nutrient Elements and Photosynthesis

Glycyrrhiza uralensis is a valuable medicinal legume, which occurs widely in arid and semi-arid regions. G. uralensis demand has risen steeply due to its high medical and commercial value. Interpret genome-wide information can stimulate the G. uralensis development as far as its increased bioactive compound levels, and plant yield are concerned. In this study, leaf nutrient concentration and photosynthetic chlorophyll index of G. uralensis were evaluated to determine the G. uralensis growth physiology in three habitats. We observed that G. uralensis nutrient levels and photosynthesis differed significantly in three regions (p < 0.05). Whole-genome re-sequencing of the sixty G. uralensis populations samples from different habitats was performed using an Illumina HiSeq sequencing platform to elucidate the distribution patterns, population evolution, and genetic diversity of G. uralensis. 150.06 Gb high-quality clean data was obtained after strict filtering. The 895237686 reads were mapped against the reference genome, with an average 89.7% mapping rate and 87.02% average sample coverage rate. A total of 6985987 SNPs were identified, and 117970 high-quality SNPs were obtained after filtering, which were subjected to subsequent analysis. Principal component analysis (PCA) based on interindividual SNPs and phylogenetic analysis based on interindividual SNPs showed that the G. uralensis samples could be categorized into central, southern, and eastern populations, which reflected strong genetic differentiation due to long periods of geographic isolation. In this study, a total of 131 candidate regions were screened, and 145 candidate genes (such as Glyur001802s00036258, Glyur003702s00044485, Glyur001802s00036257, Glyur007364s00047495, Glyur000028s00003476, and Glyur000398s00034457) were identified by selective clearance analysis based on Fst and θπ values. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed significant enrichment of 110 GO terms including carbohydrate metabolic process, carbohydrate biosynthetic process, carbohydrate derivative biosynthetic process, and glucose catabolic process (p < 0.05). Alpha-linolenic acid metabolism, biosynthesis of unsaturated fatty acids, and fatty acid degradation pathways were significantly enriched (p < 0.05). This study provides information on the genetic diversity, genetic structure, and population adaptability of the medicinal legumes, G. uralensis. The data obtained in this study provide valuable information for plant development and future optimization of breeding programs for functional genes.

Characterization of the complete chloroplast genome of Leucomeris decora Kurz (Asteraceae)

Leucomeris decora is a traditional medicinal plant that is listed as an endangered species in China. Recently, L. decora has become locally rare. Here the complete chloroplast genome of L. decora was assembled and reported for the first time. Its plastome was 151,491 bp in length, including a large single-copy region (LSC; 83,155 bp), a small single-copy region (SSC; 18,216 bp), and a pair of inverted repeated regions (IRa and IRb; 25,060 bp). The overall GC content was 37.8%, and the genome contains 134 genes, including 92 protein-coding genes, 8 rRNA genes, and 34 tRNA genes. Phylogenetic analysis of thirteen representative species from the family of Asteraceae showed that L. decora is clustered into one clade with Gerbera jamesonii with high bootstrap values, indicating a close relationship between these two species.

Demographic history and local adaptation of Myripnois dioica (Asteraceae) provide insight on plant evolution in northern China flora

The flora of northern China forms the main part of the Sino-Japanese floristic region and is located in a south-north vegetative transect in East Asia. Phylogeographic studies have demonstrated that an arid belt in this region has promoted divergence of plants in East Asia. However, little is known about how plants that are restricted to the arid belt of flora in northern China respond to climatic oscillation and environmental change. Here, we used genomic-level data of Myripnois dioica across its distribution as a representative of northern China flora to reconstruct plant demographic history, examine local adaptation related to environmental disequilibrium, and investigate the factors related to effective population size change. Our results indicate M. dioica originated from the northern area and expanded to the southern area, with the Taihang Mountains serving as a physical barrier promoting population divergence. Genome-wide evidence found strong correlation between genomic variation and environmental factors, specifically signatures associated with local adaptation to drought stress in heterogeneous environments. Multiple linear regression analyses revealed joint effects of population age, mean temperature of coldest quarter, and precipitation of wettest month on effective population size (Ne). Our current study uses M. dioica as a case for providing new insights into the evolutionary history and local adaptation of northern China flora and provides qualitative strategies for plant conservation.

Localized environmental heterogeneity drives the population differentiation of two endangered and endemic Opisthopappus Shih species

BACKGROUND

Climate heterogeneity not only indirectly shapes the genetic structures of plant populations, but also drives adaptive divergence by impacting demographic dynamics. The variable localized climates and topographic complexity of the Taihang Mountains make them a major natural boundary in Northern China that influences the divergence of organisms distributed across this region. Opisthopappus is an endemic genus of the Taihang Mountains that includes only two spatially partitioned species Opisthopappus longilobus and Opisthopappus taihangensis. For this study, the mechanisms behind the genetic variations in Opisthopappus populations were investigated.

RESULTS

Using SNP and InDel data coupled with geographic and climatic information, significant genetic differentiation was found to exist either between Opisthopappus populations or two species. All studied populations were divided into two genetic groups with the differentiation of haplotypes between the groups. At approximately 17.44 Ma of the early Miocene, O. taihangensis differentiated from O. longilobus under differing precipitation regimes due to the intensification of the Asian monsoon. Subsequently, intraspecific divergence might be induced by the dramatic climatic transformation from the mid- to late Miocene. During the Pleistocene period, the rapid uplift of the Taihang Mountains coupled with violent climatic oscillations would further promote the diversity of the two species. Following the development of the Taihang Mountains, its complex topography created geographical and ecological heterogeneity, which could lead to spatiotemporal isolation between the Opisthopappus populations. Thus the adaptive divergence might occur within these intraspecific populations in the localized heterogeneous environment of the Taihang Mountains.

CONCLUSIONS

The localized environmental events through the integration of small-scale spatial effects impacted the demographic history and differentiation mechanism of Opisthopappus species in the Taihang Mountains. The results provide useful information for us to understand the ecology and evolution of organisms in the mountainous environment from population and species perspective.

Population Differentiation and Demographic History of the Cycas taiwaniana Complex (Cycadaceae) Endemic to South China as Indicated by DNA Sequences and Microsatellite Markers

Historical geology, climatic oscillations, and seed dispersal capabilities are thought to influence the population dynamics and genetics of plants, especially for distribution-restricted and threatened species. Investigating the genetic resources within and among taxa is a prerequisite for conservation management. The Cycas taiwaniana complex consists of six endangered species that are endemic to South China. In this study, we investigated the relationship between phylogeographic history and the genetic structure of the C. taiwaniana complex. To estimate the phylogeographic history of the complex, we assessed the genetic structure and divergence time, and performed phylogenetic and demographic historical analyses. Two chloroplast DNA intergenic regions (cpDNA), two single-copy nuclear genes (SCNGs), and six microsatellite loci (SSR) were sequenced for 18 populations. The SCNG data indicated a high genetic diversity within populations, a low genetic diversity among populations, and significant genetic differentiation among populations. Significant phylogeographical structure was detected. Structure and phylogenetic analyses both revealed that the 18 populations of the C. taiwaniana complex have two main lineages, which were estimated to diverge in the Middle Pleistocene. We propose that Cycas fairylakea was incorporated into Cycas szechuanensis and that the other populations, which are mainly located on Hainan Island, merged into one lineage. Bayesian skyline plot analyses revealed that the C. taiwaniana complex experienced a recent decline, suggesting that the complex probably experienced a bottleneck event. We infer that the genetic structure of the C. taiwaniana complex has been affected by Pleistocene climate shifts, sea-level oscillations, and human activities. In addition to providing new insights into the evolutionary legacy of the genus, the genetic characterizations will be useful for the conservation of Cycas species.

Seed germination schedule and environmental context shaped the population genetic structure of subtropical evergreen oaks on the Yun-Gui Plateau, Southwest China

The evergreen broadleaved forests (EBLFs) of Southwest China have a long-term stable environment and support a diverse flora, thus forming a global biodiversity hotspot. However, the key drivers that have shaped the genetic diversity patterns of species in these EBLFs are not well understood. Quercus delavayi, Q. schottkyana, and Q. kerrii are sympatric oak species with different seed biological traits that are typical for these EBLFs. This study combined multilocus phylogeography and ecological niche modeling to screen 33 Q. delavayi populations. Their population genetic structure was inferred in comparison with previous studies on Q. schottkyana and Q. kerrii. The seed germination traits of all three species were also investigated. cpDNAs showed a significant phylogeographic structure in Q. delavayi, which was not detected in Q. schottkyana or Q. kerrii. Quercus delavayi, Q. kerrii, and Q. schottkyana exhibited different pollen-to-seed migration ratios (r = 219, 117, and 22, respectively), which are linked to the germination schedules of acorns. The distributions of Q. delavayi and Q. schottkyana remained long-term stable since the last glacial maximum (LGM) with a similar nSSR genetic gradient change along latitude. Instead, Q. kerrii experienced a prominent range expansion since the LGM with genetic diversification between the East and the West of the Tanaka line due to environmental heterogeneity. These results identify seed traits and environmental heterogeneity as two key drivers that shape the population genetic structure of EBLF trees in Southwest China. These should be considered in regional forestry conservation and management.

Genetic diversity of Bm86 sequences in Rhipicephalus (Boophilus) microplus ticks from Mexico: analysis of haplotype distribution patterns

Background

Ticks are a problem for cattle production mainly in tropical and subtropical regions, because they generate great economic losses. Acaricides and vaccines have been used to try to keep tick populations under control. This has been proven difficult given the resistance to acaricides and vaccines observed in ticks. Resistance to protein rBm86-based vaccines has been associated with the genetic diversity of Bm86 among the ectoparasite’s populations. So far, neither genetic diversity, nor spatial distribution of circulating Bm86 haplotypes, have been studied within the Mexican territory. Here, we explored the genetic diversity of 125 Bm86 cDNA gene sequences from R. microplus from 10 endemic areas of Mexico by analyzing haplotype distribution patterns to help in understanding the population genetic structure of Mexican ticks.

Results

Our results showed an average nucleotide identity among the Mexican isolates of 98.3%, ranging from 91.1 to 100%. Divergence between the Mexican and Yeerongpilly (the Bm86 reference vaccine antigen) sequences ranged from 3.1 to 7.4%. Based on the geographic distribution of Bm86 haplotypes in Mexico, our results suggest gene flow occurrence within different regions of the Mexican territory, and even the USA.

Conclusions

The polymorphism of Bm86 found in the populations included in this study, could account for the poor efficacy of the current Bm86 antigen based commercial vaccine in many regions of Mexico. Our data may contribute towards designing new, highly-specific, Bm86 antigen vaccine candidates against R. microplus circulating in Mexico.

Evolutionary Hotspots of Seed Plants in Subtropical China: A Comparison With Species Diversity Hotspots of Woody Seed Plants

Genetic diversity is a fundamental level of biodiversity. However, it is frequently neglected in conservation prioritization because intraspecific genetic diversity is difficult to measure at large scales. In this study, we synthesized population genetic or phylogeographic datasets of 33 seed plants in subtropical China into multi-species genetic landscapes. The genetic landscapes identified 18 evolutionary hotspots with high within-population genetic diversity (WGD), and among-population genetic diversity (AGD), or both. The western subtropical China is rich in AGD (possessing four major AGD hotspots), deserving a high conservation priority. We found that WGD was positively correlated with longitude, with most WGD hotspots locating in east subtropical China. The results showed that the locations of 12 of 18 evolutionary hotspots corresponded approximately to those of previously identified species diversity (SD) hotspots, however, a positive and significant correlation existed only between AGD and SD, not between WGD and SD. Therefore, spatial patterns of species richness in plants in subtropical China cannot generally be used as surrogate for their intraspecific diversity. This study identified multi-species evolutionary hotspots and correlated multi-species genetic diversity with SD across subtropical China for the first time, providing profound implications for the conservation of biodiversity in this important ecoregion.

Ecological and Genetic Divergences with Gene Flow of Two Sister Species (Leucomeris decora and Nouelia insignis) Driving by Climatic Transition in Southwest China

Understanding of the processes of divergence and speciation is a major task for biodiversity researches and may offer clearer insight into mechanisms generating biological diversity. Here, we employ an integrative approach to explore genetic and ecological differentiation of Leucomeris decora and Nouelia insignis distributed allopatrically along the two sides of the biogeographic boundary 'Tanaka Line' in Southwest China. We addressed these questions using ten low-copy nuclear genes and nine plastid DNA regions sequenced among individuals sampled from 28 populations across their geographic ranges in China. Phylogenetic, coalescent-based population genetic analyses, approximate Bayesian computation (ABC) framework and ecological niche models (ENMs) were conducted. We identified a closer phylogenetic relationship in maternal lineage of L. decora with N. insignis than that between L. decora and congeneric Leucomeris spectabilis. A deep divergence between the two species was observed and occurred at the boundary between later Pliocene and early Pleistocene. However, the evidence of significant chloroplast DNA gene flow was also detected between the marginal populations of L. decora and N. insignis. Niche models and statistical analyses showed significant ecological differentiation, and two nuclear loci among the ten nuclear genes may be under divergent selection. These integrative results imply that the role of climatic shift from Pliocene to Pleistocene may be the prominent factor for the divergence of L. decora and N. insignis, and population expansion after divergence may have given rise to chloroplast DNA introgression. The divergence was maintained by differential selection despite in the face of gene flow.

Geographical isolation and environmental heterogeneity contribute to the spatial genetic patterns of Quercus kerrii (Fagaceae)

Southwest China is one of the major global biodiversity hotspots. The Tanaka line, extending within southwestern China from its northwest to its southeast, is an important biogeographical boundary between the Sino-Japanese and Sino-Himalayan floristic regions. Understanding the evolutionary history of the regional keystone species would assist with both reconstructing historical vegetation dynamics and ongoing biodiversity management. In this research, we combined phylogeographic methodologies and species distribution models (SDMs) to investigate the spatial genetic patterns and distribution dynamics of Quercus kerrii, a dominant evergreen oak inhabiting southwest China lowland evergreen-broadleaved forests (EBLFs). A total of 403 individuals were sampled from 44 populations throughout southwest China. SDMs and mismatch distribution analysis indicated that Q. kerrii has undergone northward expansion since the Last Glacial Maximum (LGM). Quantitative analysis revealed that the range expansion of Q. kerrii since the LGM exceeded that of the sympatric mid-elevation species Quercus schottkyana, likely owing to their contrasting distribution elevations and habitat availabilities. The historical climate change since the LGM and the latitude gradient of the region played an important role in shaping the genetic diversity of Q. kerrii. The genetic differentiation index and genetic distance surface of Q. kerrii populations east of the Tanaka line exceeded those to its west. The long-term geographic isolation and environmental heterogeneity between the two sides of the Tanaka line might increase species divergence patterns and local adaptation. This study provides new insights into the historical dynamics of subtropical EBLFs and the changing biota of southwest China.

Tectonic and climatic impacts on the biota within the Red River Fault, evidence from phylogeography of Cycas dolichophylla (Cycadaceae)

Dramatic crustal deformation and river incision in Southwest China induced by the Indo-Asian collision have long been argued to contribute to the complicated landscapes, heterogeneous environment and abundant biodiversity in this region. However, biological impacts in promoting intraspecific phylogeographical subdivision and divergence along the Red River Fault zone (RRF) remain poorly understood. To investigate the possible biological effects of tectonic movements and environment variations within the RRF, the phylogeography of Cycas dolichophylla-an endemic but widely distributed Cycas in Southwest China and North Vietnam along the RRF were carried out based on four chloroplast DNA intergenic spacers (cpDNA), three nuclear DNA sequences (nDNA) and 16 simple sequence repeat variations (SSR). Two different phylogeographical patterns were detected: a Southwest-Northeast break across the RRF disclosed by chlorotypes and a China-Vietnam separation revealed by SSR. A Bayesian skyline plot from cpDNA data demonstrated a historical increasing, but a recent declining, dynamic in population size during the Pleistocene. Consequently, we infer it is the local environmental variation during Cenozoic that contributed to the complex landscape and microclimate mosaics, facilitating speciation and divergence of C. dolichophylla. Subsequently, the Quaternary climatic fluctuations coupled with human activities profoundly influenced the genetic structure and demographic history of this species.