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Oaks (Quercus L.) are ideal models to assess patterns of plant diversity. We integrated the sequence data of five chloroplast and two nuclear loci from 50 Chinese oaks to explore the phylogenetic framework, evolution and diversification patterns of the Chinese oak's lineage. The framework phylogeny strongly supports two subgenera Quercus and Cerris comprising four infrageneric sections Quercus, Cerris, Ilex and Cyclobalanopsis for the Chinese oaks. An evolutionary analysis suggests that the two subgenera probably split during the mid-Eocene, followed by intergroup divergence within the subgenus Cerris around the late Eocene. The initial diversification of sections in the subgenus Cerris was dated between the mid-Oligocene and the Oligocene-Miocene boundary, while a rapid species radiation in section Quercus started in the late Miocene. Diversification simulations indicate a potential evolutionary shift on section Quercus, while several phenotypic shifts likely occur among all sections. We found significant negative correlations between rates of the lineage diversification and phenotypic turnover, suggesting a complex interaction between the species evolution and morphological divergence in Chinese oaks. Our infrageneric phylogeny of Chinese oaks accords with the recently proposed classification of the genus Quercus. The results point to tectonic activity and climatic change during the Tertiary as possible drivers of evolution and diversification in the Chinese oak's lineage.
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Oak trees (Quercus L.) are important models for estimating abiotic impacts on the population structure and demography of long life span tree species. In this study, we generated genetic data for 17 nuclear microsatellite loci in 29 natural populations of Quercus fabri to estimate the population genetic structure. We also integrated approximate Bayesian computation (ABC) and ecological niche analysis to infer the population differentiation processes and demographic history of this oak species. The genetic analyses indicated two genetic clusters across the 29 populations collected, where most approximately corresponded to the intraspecific differentiation among populations from western and eastern China, whereas admixed populations were mainly found in central mountains of China. The best model obtained from hierarchical ABC simulations suggested that the initial intraspecific divergence of Q. fabri potentially occurred during the late Pliocene (ca. 3.99 Ma) to form the two genetic clusters, and the admixed population group might have been generated by genetic admixture of the two differentiated groups at ca. 53.76 ka. Ecological analyses demonstrated clear differentiation among the Q. fabri population structures, and association estimations also indicated significant correlations between geography and climate with the genetic variation in this oak species. Our results suggest abiotic influences, including past climatic changes and ecological factors, might have affected the genetic differentiation and demographic history of Q. fabri in subtropical China.
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Effectively identifying the genetic structure and related factors of a species can facilitate understanding the evolutionary history of the species. Phylogeographic patterns and genetic data are essential in investigating the species historical processes and diversification that response to environmental, climatic and geological influences. In this study, Specific Length Amplified Fragment Sequencing (SLAF-seq) data and ecological niche models (ENMs) are combined to identify the genetic structure and demographic modeling of Quercus spinosa, and evaluate the impacts of historical range shifts, climatic variation, and landscape factors on this species. The population topology and genetic divergence of the Cenozoic were inferred by a site frequency spectrum based composite-likelihood approach which is a novel strategy for maximizing the utility of linked SLAF markers. The overall genetic structure using model-based and model-free clustering methods was consistently identified as two geographically distinct genetic clusters. A deep divergence between two natural lineages (i.e., a western Himalaya-Hengduan Mountains lineage and an eastern Qin-ling Mountains lineage) was observed. The demographic modeling and Niche reconstruction indicated that the two groups were diverged in the late Miocene and then presented as two distinct genetic lineages. With the Quaternary glacial climate fluctuation, two groups had continuous asymmetrical secondary contact and gene exchange in the Sichuan Basin during the last glacial maximum. Besides, a significant relationship between genetic distance and geography in all individuals was identified by the Mantel test. Overall, this study 1) contributes to a better understanding of the role played by Quaternary climatic fluctuation in the present-day distributions of Q. spinosa; 2) provides a comprehensive view of the genome-wide variation of sclerophyllous forests in ecological adaptive evolution; 3) indicates that dispersal limitation and ecological divergence contribute to the genome-wide differentiation of Q. spinosa, which supports a hypothesis that complex geography and climatic changes strongly influence the evolutionary origin and history of the species.
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Southwest China is an important biodiversity hotspot. The interactions among the complex topography, climate change, and ecological factors in the dry-hot valley areas in southwest China may have profoundly affected the genetic structure of plant species in this region. In this study, we determined the effects of the Tanaka Line on genetic variation in the wild Bombax ceiba tree in southwest China. We sampled 224 individuals from 17 populations throughout the dry-hot valley regions. Six polymorphic expressed sequence tag-simple sequence repeat primers were employed to sequence the PCR products using the first-generation Sanger technique. The analysis based on population genetics suggested that B. ceiba exhibited a high level of gene diversity (HE: 0.2377-0.4775; I: 0.3997-0.7848). The 17 populations were divided into two groups by cluster analysis, which corresponded to geographic characters on each side of the Tanaka Line. In addition, a Mantel test indicated that the phylogeographic structure among the populations could be fitted to the isolation-by-distance model (r2 = .2553, p < .001). A barrier test indicated that there were obstacles among populations and between the two groups due to complex terrain isolation and geographic heterogeneity. We inferred that the Tanaka Line might have promoted the intraspecific phylogeographic subdivision and divergence of B. ceiba. These results provide new insights into the effects of the Tanaka Line on genetic isolation and population differentiation of plant species in southwest China.
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PREMISE OF THE STUDY: The first set of expressed sequence tag-simple sequence repeat (EST-SSR) markers were developed and characterized for Speranskia tuberculata (Euphorbiaceae), a traditional medicinal plant endemic to northern China, to explore the effects of recent habitat fragmentation on the genetic diversity and structure of this species. METHODS AND RESULTS: In this study, a total of 18 novel polymorphic microsatellite (EST-SSR) markers were developed for S. tuberculata using high-throughput transcriptome sequencing. Analysis of 24 individuals of S. tuberculata from four natural populations revealed their robust polymorphic reliability. The number of alleles per locus ranged from two to 11, while the expected and observed heterozygosity per marker varied from 0.187 to 0.827 and 0.042 to 0.917, respectively. Of these markers, 13 showed good amplification results in the closely related species S. cantonensis. CONCLUSIONS: These newly generated SSR markers are expected to provide novel tools for genetic studies of S. tuberculata, which will contribute to the conservation and sustainable use of the species' wild genetic resources.
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PREMISE OF THE STUDY: Bombax ceiba (Malvaceae), commonly known as silk cotton tree, is a multipurpose tree species of tropical forests. Novel expressed sequence tag-simple sequence repeat (EST-SSR) markers were developed and characterized for the species using transcriptome analysis. METHODS AND RESULTS: A total of 33 new EST-SSR markers were developed for B. ceiba, of which 13 showed polymorphisms across the 24 individuals from four distant populations tested in the study. The results showed that the number of alleles per polymorphic locus ranged from two to four, and the expected heterozygosity and observed heterozygosity per locus varied from 0.043 to 0.654 and from 0 to 0.609, respectively. CONCLUSIONS: These newly developed EST-SSR markers can be used in phylogeographic and population genetic studies to investigate the origin of B. ceiba populations. Furthermore, these EST-SSR markers could also greatly promote the development of molecular breeding studies pertaining to silk cotton tree.