Future carbon sequestration potential in a widespread transcontinental boreal tree species: Standing genetic variation matters!

Climate change (CC) necessitates reforestation/afforestation programs to mitigate its impacts and maximize carbon sequestration. But comprehending how tree growth, a proxy for fitness and resilience, responds to CC is critical to maximize these programs' effectiveness. Variability in tree response to CC across populations can notably be influenced by the standing genetic variation encompassing both neutral and adaptive genetic diversity. Here, a framework is proposed to assess tree growth potential at the population scale while accounting for standing genetic variation. We applied this framework to black spruce (BS, Picea mariana [Mill] B.S.P.), with the objectives to (1) determine the key climate variables having impacted BS growth response from 1974 to 2019, (2) examine the relative roles of local adaptation and the phylogeographic structure in this response, and (3) project BS growth under two Shared Socioeconomic Pathways while taking standing genetic variation into account. We modeled growth using a machine learning algorithm trained with dendroecological and genetic data obtained from over 2600 trees (62 populations divided in three genetic clusters) in four 48-year-old common gardens, and simulated growth until year 2100 at the common garden locations. Our study revealed that high summer and autumn temperatures negatively impacted BS growth. As a consequence of warming, this species is projected to experience a decline in growth by the end of the century, suggesting maladaptation to anticipated CC and a potential threat to its carbon sequestration capacity. This being said, we observed a clear difference in response to CC within and among genetic clusters, with the western cluster being more impacted than the central and eastern clusters. Our results show that intraspecific genetic variation, notably associated with the phylogeographic structure, must be considered when estimating the response of widespread species to CC.

Population genetic patterns across the native and invasive range of a widely distributed seagrass: Phylogeographic structure, invasive history and conservation implications.

Aim: The seagrass Zostera japonica is a dramatically declined endemic species in the Northwestern Pacific from the (sub)tropical to temperate areas, however, it is also an introduced species along the Pacific coast of North America from British Columbia to northern California. Understanding the population's genetic patterns can inform the conservation and management of this species. Location: North Pacific. Methods: We used sequences of the nuclear rDNA internal transcribed spacer (ITS) and chloroplast trnK intron maturase (matK), and 24 microsatellite loci to survey 34 native and nonnative populations (>1000 individuals) of Z. japonica throughout the entire biogeographic range. We analysed the phylogeographic relationship, population genetic structure and genetic diversity of all populations and inferred possible origins and invasion pathways of the nonnative ones. Results: All markers revealed a surprising and significant deep divergence between northern and southern populations of Z. japonica in the native region separated by a well-established biogeographical boundary. A secondary contact zone was found along the coasts of South Korea and Japan. Nonnative populations were found to originate from the central Pacific coast of Japan with multiple introductions from at least two different source populations, and secondary spread was likely aided by waterfowl. Main Conclusions: The divergence of the two distinct clades was likely due to the combined effects of historical isolation, adaptation to distinct environments and a contemporary physical barrier created by the Yangtze River, and the warm northward Kuroshio Current led to secondary contact after glacial separation. Existing exchanges among the nonnative populations indicate the potential for persistence and further expansion. This study not only helps to understand the underlying evolutionary potential of a widespread seagrass species following global climate change but also provides valuable insights for conservation and restoration.

Discerning structure versus speciation in phylogeographic analysis of Seepage Salamanders (Desmognathus aeneus) using demography, environment, geography, and phenotype.

Numerous mechanisms can drive speciation, including isolation by adaptation, distance, and environment. These forces can promote genetic and phenotypic differentiation of local populations, the formation of phylogeographic lineages, and ultimately, completed speciation. However, conceptually similar mechanisms may also result in stabilizing rather than diversifying selection, leading to lineage integration and the long-term persistence of population structure within genetically cohesive species. Processes that drive the formation and maintenance of geographic genetic diversity while facilitating high rates of migration and limiting phenotypic differentiation may thereby result in population genetic structure that is not accompanied by reproductive isolation. We suggest that this framework can be applied more broadly to address the classic dilemma of "structure" versus "species" when evaluating phylogeographic diversity, unifying population genetics, species delimitation, and the underlying study of speciation. We demonstrate one such instance in the Seepage Salamander (Desmognathus aeneus) from the southeastern United States. Recent studies estimated up to 6.3% mitochondrial divergence and four phylogenomic lineages with broad admixture across geographic hybrid zones, which could potentially represent distinct species supported by our species-delimitation analyses. However, while limited dispersal promotes substantial isolation by distance, microhabitat specificity appears to yield stabilizing selection on a single, uniform, ecologically mediated phenotype. As a result, climatic cycles promote recurrent contact between lineages and repeated instances of high migration through time. Subsequent hybridization is apparently not counteracted by adaptive differentiation limiting introgression, leaving a single unified species with deeply divergent phylogeographic lineages that nonetheless do not appear to represent incipient species.

Phylogeography and ecological niche modeling implicate multiple microrefugia of Swertia tetraptera during quaternary glaciations.

BACKGROUND: Climate fluctuations during the Pleistocene and mountain uplift are vital driving forces affecting geographic distribution. Here, we ask how an annual plant responded to the Pleistocene glacial cycles. METHODS: In this study, we analyzed the population demographic history of the annual herb Swertia tetraptera Maxim (Gentianaceae) endemic to Qinghai-Tibetan Plateau (QTP). A total of 301 individuals from 35 populations of S. tetraptera were analyzed based on two maternally inherited chloroplast fragments (trnL-trnF and trnS-trnG). Phylogeographic analysis was combined with species distribution modeling to detect the genetic variations in S. tetraptera. RESULTS: The genetic diversity of S. tetraptera was high, likely due to its wide natural range, high proportion of endemic haplotypes and evolutionary history. Fifty-four haplotypes were identified in S. tetraptera. Only a few haplotypes were widespread (Hap_4, Hap_1, Hap_3), which were dispersed throughout the present geographical range of S. tetraptera, while many haplotypes were confined to single populations. The cpDNA dataset showed that phylogeographic structuring was lacking across the distribution range of S. tetraptera. Analyses of molecular variance showed that most genetic variation was found within populations (70.51%). In addition, the relationships of the haplotypes were almost completely unresolved by phylogenetic reconstruction. Both mismatch distribution analysis and neutrality tests showed a recent expansion across the distribution range of S. tetraptera. The MaxEnt analysis showed that S. tetraptera had a narrow distribution range during the Last Glacial Maximum (LGM) and a wide distribution range during the current time, with predictions into the future showing the distribution range of S. tetraptera expanding. CONCLUSION: Our study implies that the current geographic and genetic distribution of S. tetraptera is likely to have been shaped by Quaternary periods. Multiple microrefugia of S. tetraptera existed during Quaternary glaciations. Rapid intraspecific diversification and hybridization and/or introgression may have played a vital role in shaping the current distribution patterns of S. tetraptera. The distribution range of S. tetraptera appeared to have experienced contraction during the LGM; in the future, when the global climate becomes warmer with rising carbon dioxide levels, the distribution of S. tetraptera will expand.

Corrigendum: Out of the Qinghai-Tibetan plateau: origin, evolution and historical biogeography of Morchella (both Elata and Esculenta clades).

[This corrects the article DOI: 10.3389/fmicb.2022.1078663.].

Population structure and genome-wide evolutionary signatures reveal putative climate-driven habitat change and local adaptation in the large yellow croaker.

The large yellow croaker (Larimichthys crocea) is one of the most economically valuable marine fish in China and is a notable species in ecological studies owing to a serious collapse of wild germplasm in the past few decades. The stock division and species distribution, which have important implications for ecological protection, germplasm recovery, and fishery resource management, have been debated since the 1960s. However, it is still uncertain even how many stocks exist in this species. To address this, we evaluated the fine-scale genetic structure of large yellow croaker populations distributed along the eastern and southern Chinese coastline based on 7.64 million SNP markers. Compared with the widely accepted stock boundaries proposed in the 1960s, our results revealed that a climate-driven habitat change probably occurred between the Naozhou (Nanhai) Stock and the Ming-Yuedong (Mindong) Stock. The boundary between these two stocks might have shifted northwards from the Pearl River Estuary to the northern area of the Taiwan Strait, accompanied by highly asymmetric introgression. In addition, we found divergent landscapes of natural selection between the stocks inhabiting northern and southern areas. The northern population exhibited highly agminated signatures of strong natural selection in genes related to developmental processes, whereas moderate and interspersed selective signatures were detected in many immune-related genes in the southern populations. These findings establish the stock status and genome-wide evolutionary landscapes of large yellow croaker, providing a basis for conservation, fisheries management and further evolutionary biology studies. Supplementary Information: The online version contains supplementary material available at 10.1007/s42995-023-00165-2.

Climatic oscillation promoted diversification of spinous assassin bugs during Pleistocene glaciation.

Insect speciation is among the most fascinating topics in evolutionary biology; however, its underlying mechanisms remain unclear. Allopatric speciation represents one of the major types of speciation and is believed to have frequently occurred during glaciation periods, when climatic oscillation may have caused suitable habitats to be fragmented repeatedly, creating geographical isolation among populations. However, supporting evidence for allopatric speciation of insects in East Asia during the Pleistocene glaciation remains lacking. We aim to investigate the effect of climatic oscillation during the Pleistocene glaciation on the diversification pattern and evolutionary history of hemipteran insects and to test the hypothesis of Pleistocene species stability using spinous assassin bugs Sclomina (Hemiptera: Reduviidae), a small genus widely distributed in southern China but was later found to have cryptic species diversity. Here, using the whole mitochondrial genome (mitogenome) and nuclear ribosomal RNA genes, we investigated both interspecific and intraspecific diversification patterns of spinous assassin bugs. Approximate Bayesian computation, ecological niche modeling, and demographic history analyses were also applied to understand the diversification process and driven factors. Our data suggest that the five species of Sclomina are highly diverged, despite three of them currently being cryptic. Speciation occurred during the Pleistocene when suitable distribution areas were possibly fragmented. Six phylogeographic groups in the type species S. erinacea were identified, among which two groups underwent expansion during the early Last Glacial Period and after Last Glacier Maximum. Our analyses suggest that this genus may have experienced climate-driven habitat fragmentation and postglacial expansion in the Pleistocene, promoting allopatric speciation and intraspecific diversification. Our results reveal underestimated species diversity in a small insect group and illustrate a remarkable example of allopatric speciation of insects in East Asia promoted by Pleistocene climatic oscillations. These findings provide important insights into the speciation processes and aid the conservation of insect species diversity.

Comparative evolutionary history of two closely related desert plant, Convolvulus tragacanthoide and Convolvulus gortschakovii (Convolvulaceae) from northwest China.

Desert ecosystems are one of the most fragile ecosystems on Earth. The study of the effects of paleoclimatic and geological changes on genetic diversity, genetic structure, and species differentiation of desert plants is not only helpful in understanding the strategies of adaptation of plants to arid habitats, but can also provide reference for the protection and restoration of vegetation in desert ecosystem. Northwest China is an important part of arid regions in the northern hemisphere. Convolvulus tragacanthoides and Convolvulus gortschakovii are closely related and have similar morphology. Through our field investigation, we found that the annual precipitation of the two species distribution areas is significantly different. Thus, C. tragacanthoides and C. gortschakovii provide an ideal comparative template to investigate the evolutionary processes of closely related species, which have adapted to different niches in response to changes in paleogeography and paleoclimate in northwest China. In this study, we employed phylogeographical approaches (two cpDNA spacers: rpl14-rpl36 and trnT-trnY) and species distribution models to trace the demographic history of C. tragacanthoides and C. gortschakovii, two common subshrubs and small shrubs in northwest China. The results showed the following: (1) Populations of C. tragacanthoides in northwest China were divided into three groups: Tianshan Mountains-Ili Valley, west Yin Mountains-Helan Mountains-Qinglian Mountains, and Qinling Mountains-east Yin Mountains. There was a strong correlation between the distribution of haplotypes and the floristic subkingdom. The three groups corresponded to the Eurasian forest subkingdom, Asian desert flora subkingdom, and Sino-Japanese floristic regions, respectively. Thus, environmental differences among different flora may lead to the genetic differentiation of C. tragacanthoides in China. (2) The west Yin Mountains-Helan Mountains-Qinglian Mountains, and Qinling Mountains-east Yin Mountains were thought to form the ancestral distribution range of C. tragacanthoides. (3) C. tragacanthoides and C. gortschakovii adopted different strategies to cope with the Pleistocene glacial cycle. Convolvulus tragacanthoides contracted to the south during the glacial period and expanded to the north during the interglacial period; and there was no obvious north-south expansion or contraction of C. gortschakovii during the glacial cycle. (4) The interspecific variation of C. tragacanthoides and C. gortschakovii was related to the orogeny in northwest China caused by the uplift of the Tibetan Plateau during Miocene. (5) The 200 mm precipitation line formed the dividing line between the niches occupied by C. tragacanthoides and C. gortschakovii, respectively. In this study, from the perspective of precipitation, the impact of the formation of the summer monsoon limit line on species divergence and speciation is reported, which provides a new perspective for studying the response mechanism of species to the formation of the summer monsoon line, and also provides a clue for predicting how desert plants respond to future environmental changes.

Out of the Qinghai-Tibetan plateau: Origin, evolution and historical biogeography of Morchella (both Elata and Esculenta clades).

Introduction: Morchella has become a research hotspot because of its wide distribution, delicious taste, and phenotypic plasticity. The Qinghai-Tibet Plateau subkingdoms (QTPs) are known as the cradle of Ice age biodiversity. However, the diversity of Morchella in the QTPs has been poorly investigated, especially in phylogenetic diversity, origin, and biogeography. Methods: The genealogical concordance phylogenetic species recognition (GCPSR, based on Bayesian evolutionary analysis using sequences from the internal transcribed spacer (ITS), nuclear large subunit rDNA (nrLSU), translation elongation factor 1-α (EF1-α), and the largest and second largest subunits of RNA polymerase II (RPB1 and RPB2)), differentiation time estimation, and ancestral region reconstruction were used to infer Morchella's phylogenetic relationships and historical biogeography in the QTPs. Results: Firstly, a total of 18 Morchella phylogenetic species are recognized in the QTPs, including 10 Elata clades and 8 Esculenta clades of 216 individuals Secondly, the divergences of the 18 phylogenetic species were 50.24-4.20 Mya (Eocene-Pliocene), which was closely related to the geological activities in the QTPs. Furthermore, the ancestor of Morchella probably originated in the Northern regions (Qilian Shan, Elata cade) and southwestern regions (Shangri-La, Esculenta clade) of QTPs and might have migrated from North America (Rufobrunnea clade) via Beringian Land Bridge (BLB) and Long-Distance Dispersal (LDD) expansions during the Late Cretaceous. Moreover, as the cradle of species origin and diversity, the fungi species in the QTPs have spread out and diffused to Eurasia and South Africa starting in the Paleogene Period. Conclusion: This is the first report that Esculenta and Elata clade of Morchella originated from the QTPs because of orogenic, and rapid differentiation of fungi is strongly linked to geological uplift movement and refuge in marginal areas of the QTPs. Our findings contribute to increasing the diversity of Morchella and offer more evidence for the origin theory of the QTPs.

Geographic patterns of genomic diversity and structure in the C4 grass Panicum hallii across its natural distribution.

Geographic patterns of within-species genomic diversity are shaped by evolutionary processes, life history and historical and contemporary factors. New genomic approaches can be used to infer the influence of such factors on the current distribution of infraspecific lineages. In this study, we evaluated the genomic and morphological diversity as well as the genetic structure of the C4 grass Panicum hallii across its complex natural distribution in North America. We sampled extensively across the natural range of P. hallii in Mexico and the USA to generate double-digestion restriction-associated DNA (ddRAD) sequence data for 423 individuals from 118 localities. We used these individuals to study the divergence between the two varieties of P. hallii, P. hallii var. filipes and P. hallii var. hallii as well as the genetic diversity and structure within these groups. We also examined the possibility of admixture in the geographically sympatric zone shared by both varieties, and assessed distribution shifts related with past climatic fluctuations. There is strong genetic and morphological divergence between the varieties and consistent genetic structure defining seven genetic clusters that follow major ecoregions across the range. South Texas constitutes a hotspot of genetic diversity with the co-occurrence of all genetic clusters and admixture between the two varieties. It is likely a recolonization and convergence point of populations that previously diverged in isolation during fragmentation events following glaciation periods.

Maternal origins, population structure and demographic history of ten Chinese indigenous goat breeds from Yunnan.

Yunnan as a frontier zone that connects China with South and Southeast Asia, has 11 well-recognized goat breeds. However, the knowledge about maternal origins, population structure and demographic history of Chinese indigenous goats from Yunnan is limited. In this study, we analysed a 481-bp fragment of first hypervariable segment (HVSI) of the mitochondrial DNA (mtDNA) control region sequences of 749 individuals from 10 Yunnan indigenous goat breeds, of which 556 sequences were newly determined. There were 110 polymorphic sites that defined 158 haplotypes among all sequences. The haplotype and nucleotide diversity of these breeds ranged from 0.782 ± 0.079 to 0.982 ± 0.015 and from 0.028 ± 0.003 to 0.043 ± 0.005, respectively. Phylogenetic analysis identified two lineages A and B, of which the lineage A had higher frequency (68.1%) and distributed in all Yunnan breeds. We combined previously reported sequences with our sequences belonging to the lineage B and detected two subclades B1 and B2, in which the B1 subclade shared individuals from Eastern Asia, Southeast Asia and Southern Asia. Given higher level of diversity and more unique haplotypes, the B2 subclade probably originated from Southwestern China. The haplotype network, analysis of molecular variance (AMOVA) and a Mantel test revealed no significant phylogeographic structuring among Yunnan goat breeds. This can be explained by high gene flow and genetic admixture among these breeds from different geographic regions in Yunnan. Additionally, both the lineages A and B reflected different demographic histories. This study will provide a scientific basis for the conservation and utilization of Yunnan indigenous goats.

Phylogeographic structures of the host insects of Ophiocordyceps sinensis.

A fungus-insect complex, known as DongChong XiaCao, is formed from the infection of the hepialid larvae by the fungus Ophiocordyceps sinensis, which is endemic to the Qinghai-Tibetan Plateau (QTP). Due to previously limited sample collection size, the data about the diversity and structure of the host insect was insufficient and lacked details. The purpose of this study was aimed to discuss the diversity and phylogeography of the host insects of O. sinensis with a large-scale sampling. The mitochondrial cytochrome oxidase I gene (cox1) was sequenced and analyzed among 710 samples representing 88 geographic locations. 205 haplotypes of cox1 were identified from all the 710 samples and 4 phylogenetic clades with 12 subclades were identified. Instead of the single latitude-based divergence suggested previously, three distribution patterns were deduced to correspond to the phylogeographic structures, including but not limited to the co-existence of a wide and specific local phylogeographic distribution structures. Two separate genetic diversity and differentiation centers, namely the northwestern Yunnan and the southeastern Tibet were identified. Dating analyses from three calibrations supported that the divergence of the 4 clades occurred in the Oligocene-Miocene period (30.54-13.66 million years ago) (Ma), which were connected with the second and third geological movements of the QTP (17-25, 8-13 Ma). Our results provide a more detailed understanding of the divergence and distribution patterns of the host insects of O. sinensis.

Chloroplast genome analysis of box-ironbark Eucalyptus.

Eucalyptus L'Hérit. (Myrtaceae) is a taxonomically complex and highly speciose genus that dominates much of Australia's woody vegetation. However, very little information is available about the molecular biology and chloroplast diversity of certain groups, such as Eucalyptus section Adnataria, which is found in many woodland habitats of eastern Australia. We report four new complete chloroplast genomes of Eucalyptus, including three genomes from species previously lacking any chloroplast reference sequences. Plastomes of E. albens, E. conica, E. crebra and E. melliodora assembled using a de novo approach were shown to be largely identical to each other, and similar in size and structure to previously published chloroplast genomes from Eucalyptus. A total of 132 genes (114 single-copy genes and 18 duplicated genes in the IR regions) were identified, and shown to be highly conserved in terms of gene order, content and organization. Slightly higher divergence in the intergenic spacers was identified through comparative genomic analyses. Chloroplast sequences of 35 additional individuals representing 12 species were assembled using a reference guided approach. Rates of nucleotide substitution varied among the protein coding genes, with 17 genes under possible positive selection, and 29 invariant genes. Phylogenetic analysis of either the whole reconstructed plastome sequences or the individual genes revealed extreme discordance with expected species boundaries or higher-level relationships. Plastome relationships were better predicted by geography than by nuclear DNA or taxonomic relationships, suggesting a substantial influence of gene flow over and above the effects of incomplete lineage sorting. These results provide resources for future research and valuable insights into the prevalence of interspecific gene flow among Eucalyptus species.

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.

Phylogeography and genetic connectivity of the marine macro-alga Sargassum ilicifolium (Phaeophyceae, Ochrophyta) in the northwestern Pacific1.

The evolutionary influences of historical and contemporary factors on the population connectivity and phylogeographic structure of a brown seaweed, Sargassum ilicifolium, were elucidated using the nuclear ITS2 and mitochondrial COI markers for the collections newly sampled within its distribution range in the northwestern Pacific (NWP). Significant genetic structure at variable levels was identified between populations (pairwise FST ) and among populations grouped by geographical proximity (ΦCT among regions). The adjacent groups of populations with moderate structure revealed from AMOVA appeared to have high genetic connectivity. However, a lack of genealogical concordance with the geographic distribution was uncovered for S. ilicifolium from the NWP. Such genetic homogeneity is interpreted as a result of the interaction between postglacial recolonization and dynamic oceanic current regimes in the region. Two separated glacial refugia, the South China Sea and the Okinawa Trough, in the marginal seas of east China were recognized based on the presence of endemic haplotypes and high haplotype diversity in the populations at southern China and northeast of Taiwan. Populations persisting in these refugia may have served as the source for recolonization in the NWP with the rise of sea level during the warmer interglacial periods. The role of oceanic currents in maintaining genetic connectivity of S. ilicifolium in the region was further corroborated by the coherence between the direction of oceanic currents and that of gene flow, especially along the eastern coast of Taiwan. This study underlines the interaction between historical postglacial recolonization and contemporary coastal hydrodynamics in contributing to population connectivity and distribution for this tropical seaweed in the NWP.

Phylogeography of Eomecon chionantha in subtropical China: the dual roles of the Nanling Mountains as a glacial refugium and a dispersal corridor.

BACKGROUND: Mountains have not only provided refuge for species, but also offered dispersal corridors during the Neogene and Quaternary global climate changes. Compared with a plethora of studies on the refuge role of China's mountain ranges, their dispersal corridor role has received little attention in plant phylogeographic studies. Using phylogeographic data of Eomecon chionantha Hance (Papaveraceae), this study explicitly tested whether the Nanling Mountains, which spans from west to east for more than 1000 km in subtropical China, could have functioned as a dispersal corridor during the late Quaternary in addition to a glacial refugium. RESULTS: Our analyses revealed a range-wide lack of phylogeographic structure in E. chionantha across three kinds of molecular markers [two chloroplast intergenic spacers, nuclear ribosomal internal transcribed spacer (nrITS), and six nuclear microsatellite loci]. Demographic inferences based on chloroplast and nrITS sequences indicated that E. chionantha could have experienced a strong postglacial range expansion between 6000 and 1000 years ago. Species distribution modelling showed that the Nanling Mountains and the eastern Yungui Plateau were the glacial refugia of E. chionantha. Reconstruction of dispersal corridors indicated that the Nanling Mountains also have acted as a corridor of population connectivity for E. chionantha during the late Quaternary. CONCLUSIONS: Our results suggest that the Nanling Mountains may acted dual roles as a dispersal corridor in east-west direction and as a glacial refugium in subtropical China during the late Quaternary. The population connectivity mediated by the mountain range and a strong postglacial range expansion are the most likely reasons for the lack of phylogeographic structure in E. chionantha. The hypothesis of dual roles of the mountain range presented here sheds new insights into the phylogeographic patterns of organisms in subtropical China.

Phylogeographic structure, cryptic speciation and demographic history of the sharpbelly (Hemiculter leucisculus), a freshwater habitat generalist from southern China.

BACKGROUND: Species with broad distributions frequently divide into multiple genetic forms and may therefore be viewed as "cryptic species". Here, we used the mitochondrial cytochrome b (Cytb) and 12 nuclear DNA loci to investigate phylogeographic structures of the sharpbelly (Hemiculter leucisculus) in rivers in southern China and explored how the geological and climatic factors have shaped the genetic diversity and evolutionary history of this species. RESULTS: Our mitochondrial phylogenetic analysis identified three major lineages (lineages A, B, and C). Lineages B and C showed a relatively narrower geographic distribution, whereas lineage A was widely distributed in numerous drainages. Divergence dates suggested that H. leucisculus populations diverged between 1.61-2.38 Ma. Bayesian species delimitation analysis using 12 nuclear DNA loci indicated the three lineages probably represented three valid taxa. Isolation-with-migration (IM) analysis found substantial gene flow has occurred among the three lineages. Demographic analyses showed that lineages B and C have experienced rapid demographic expansion at 0.03 Ma and 0.08 Ma, respectively. CONCLUSIONS: Hemiculter leucisculus populations in drainages in southern China comprise three mtDNA lineages, and each of which may represent a separate species. Intense uplift of the Qinghai-Tibetan Plateau, evolution of Asian monsoons, changes in paleo-drainages, and poor dispersal ability may have driven the divergence of the three putative species. However, gene flow occurs among the three lineages. Climatic fluctuations have a prominent impact on the populations from the lineages B and C, but exerted little influence on the lineage A.

Extreme Glacial Legacies: A Synthesis of the Antarctic Springtail Phylogeographic Record.

We review current phylogeographic knowledge from across the Antarctic terrestrial landscape with a focus on springtail taxa. We describe consistent patterns of high genetic diversity and structure among populations which have persisted in glacial refugia across Antarctica over both short (10 Mya) timescales. Despite a general concordance of results among species, we explain why location is important in determining population genetic patterns within bioregions. We complete our review by drawing attention to the main limitations in the field of Antarctic phylogeography, namely that the scope of geographic focus is often lacking within studies, and that large gaps remain in our phylogeographic knowledge for most terrestrial groups.