Influence of geography and environment on patterns of genetic differentiation in a widespread submerged macrophyte, Eurasian watermilfoil (Myriophyllum spicatum L., Haloragaceae)

Genetic structure and conservation implications of Lancea tibetica (Mazaceae), a traditional Tibetan medicinal plant endemic to the Qinghai- Tibet Plateau

BACKGROUND

Allopatric divergence is often initiated by geological uplift and climate oscillations. Qinghai-Tibet Plateau is an excellent place for such research because the plants of this area have experienced such historical processes as glacial contraction, interglacial expansion and geographical isolation. Here in this study, we used Genotyping-By-Sequencing data to investigate allopatric divergence of Lancea tibetica, an endemic herb to the Qinghai-Tibet Plateau. A total of 12,005 high-quality single nucleotide polymorphisms were obtained from 183 individuals of 23 natural distribution areas.

RESULTS

Our results confirm that L. tibetica is divided into Northern and Southern groups, separated by the Tangula Mountains, Nyainqentanglha Mountains, and the Salween River. Demographic modeling indicated a bottleneck event around 300 kya, followed by gene flow and a recent expansion in both groups. Geographic isolation and climatic variation are likely the primary factors shaping the population structure of this species. Species distribution models reveal that elevation is the most significant factor influencing the distribution of L. tibetica, followed by precipitation and temperature. In scenarios of future global warming, suitable habitats for L. tibetica are likely to be significantly reduced, with an anticipated migration to higher altitudes. Given the current and projected distribution patterns of L. tibetica, the implementation of in-situ conservation and commercial cultivation measures is particularly urgent.

CONCLUSIONS

Our study contributes insights into understanding the genetic variation and distribution pattern of species in the Qinghai-Tibet Plateau and its adjacent areas, serving as a valuable reference for future conservation efforts.

Signatures of local adaptation and maladaptation to future climate in wild Zizania latifolia

Global climate change poses challenges to agricultural production and food security. Assessing the adaptive capacity of crop wild relatives to future climate is important for protecting key germplasm resources and breeding new crops. We performed population genomics, genotype-environment association analyses, and genomic offset assessment of Chinese wild rice, Zizania latifolia, a crop wild relative and potential new grain crop, based on 168 individuals from 42 populations. We found two genetic lineages in Z. latifolia, corresponding to the south and north of its range, that diverged during the Late Pleistocene. We also identified lineage-specific positively selected genes associated with flower development and flowering, seed shattering, pathogen defense response and cold tolerance. We further found that populations from southeastern China are the most maladapted to future climate and should be prioritized for conservation. Our findings provide important clues for leveraging existing genetic diversity to identify important germplasm resources and create climate-resilient crops.

Genomic insights into local adaptation in the Asiatic toad Bufo gargarizans, and its genomic offset to climate warming

Genomic signatures of local adaptation have been identified in many species but remain sparsely studied in amphibians. Here, we explored genome-wide divergence within the Asiatic toad, Bufo gargarizans, to study local adaptation and genomic offset (i.e., the mismatch between current and future genotype-environment relationships) under climate warming scenarios. We obtained high-quality SNP data for 94 Asiatic toads from 21 populations in China to study spatial patterns of genomic variation, local adaptation, and genomic offset to warming in this wide-ranging species. Population structure and genetic diversity analysis based on high-quality SNPs revealed three clusters of B. gargarizans in the western, central-eastern, and northeastern portions of the species' range in China. Populations generally dispersed along two migration routes, one from the west to the central-east and one from the central-east to the northeast. Both genetic diversity and pairwise F ST were climatically correlated, and pairwise F ST was also correlated with geographic distance. Spatial genomic patterns in B. gargarizans were determined by the local environment and geographic distance. Global warming will increase the extirpation risk of B. gargarizans.

Hybridization and diversity of aquatic macrophyte Sparganium L. (Typhaceae) as revealed by high-throughput nrDNA sequencing

Sparganium is an emergent aquatic macrophyte widely spread in temperate and subtropical zones. Taxa of this genus feature high phenotypic plasticity and can produce interspecific hybrids. By means of high-throughput sequencing of the internal transcribed spacer (ITS1) of 35S rDNA, the status of 15 Eurasian Sparganium species and subspecies was clarified and the role of hybridization events in the recent evolution of the genus was investigated. It has been shown that a number of species such as S. angustifolium, S. fallax and S. subglobosum have homogenized rDNA represented by one major ribotype. The rDNA of other taxa is represented by two or more major ribotypes. Species with high rDNA heterogeneity are apparently of hybrid origin. Based on the differences in rDNA patterns, intraspecific diversity was identified in S. probatovae and S. emersum. Thus, we have concluded that Sparganium has extensive interspecific hybridization at the subgenus level, and there may also be occasional hybridization between species from different subgenera.

Effects of highland environments on clonal diversity in aquatic plants: An interspecific comparison study on the Qinghai-Tibetan Plateau

Clonal reproduction is one of the most distinctive characteristics of plants and is common and diverse in aquatic macrophytes. The balance between sexual and asexual reproduction is affected by various conditions, especially adverse environments. However, we know little about clonal diversity of aquatic plants under suboptimal conditions, such as at high altitudes, and having this information would help us understand how environmental gradients influence patterns of clonal and genetic variation in freshwater species. The microsatellite data of four aquatic taxa in our previous studies were revisited to estimate clonal and genetic diversity on the Qinghai-Tibetan Plateau. Clonal diversity among different genetic groups was compared. Local environmental features were surveyed. Beta regressions were used to identify the environmental factors that significantly explained clonal diversity for relative taxon. The level of clonal diversity from high to low was Stuckenia filiformis > Hippuris vulgaris > Myriophyllum species > Ranunculus section Batrachium species. A positive correlation between clonal and genetic diversity was identified for all taxa, except H. vulgaris. Clonal diversity was affected by climate in S. filiformis and by the local environment in H. vulgaris. For Myriophyllum spp., low elevation and high sediment nutrition were significant for sexual recruitment. The environmental effects on clonal diversity were not significant in R. sect. Batrachium spp. Clonal diversity of aquatic plants is moderate to high and varies greatly in highlands. The effects of breeding systems and environmental factors on the patterns of clonal variation were identified. Elevational gradients, climates and local conditions play different roles in clonal diversity among relative taxon. Our results highlight the importance of sexual recruitment in alpine aquatic plant populations and the influence of environmental factors on the genetic patterns in freshwater species at local and regional scales.

Legacy of supervolcanic eruptions on population genetic structure of brown kiwi

Supervolcanoes are volcanoes capable of mega-colossal eruptions that emit more than 1,000 km³ of ash and other particles.¹ The earth's most recent mega-colossal eruption was the Oruanui eruption of the Taupo supervolcano 25,580 years before present (YBP) on the central North Island of New Zealand.² This eruption blanketed major swaths of the North Island in thick layers of ash and igneous rock,^2,3 devastating habitats and likely causing widespread population extinctions.^4-7 An additional devastating super-colossal eruption (>100 km³) of the Taupo supervolcano occurred approximately 1,690 YBP.⁸ The impacts of such massive but ephemeral natural disasters on contemporary population genetic structure remain underexplored. Here, we combined data for 4,951 SNPs with spatially explicit demographic and coalescent models within an approximate Bayesian computation framework to test the drivers of genetic structure in brown kiwi (Apteryx mantelli). Our results strongly support the importance of eruptions of the Taupo supervolcano in restructuring pre-existing geographic patterns of population differentiation and genetic diversity. Range shifts due to climatic oscillations-a frequent explanation for genetic structure⁹-are insufficient to fully explain the empirical data. Meanwhile, recent range contraction and fragmentation due to historically documented anthropogenic habitat alteration adds no explanatory power to our models. Our results support a major role for cycles of destruction and post-volcanic recolonization in restructuring the population genomic landscape of brown kiwi and highlight how ancient and ephemeral mega-disasters may leave a lasting legacy on patterns of intraspecific genetic variation.

Extensive Sympatry and Frequent Hybridization of Ecologically Divergent Aquatic Plants on the Qinghai-Tibetan Plateau

Hybridization has fascinated biologists in recent centuries for its evolutionary importance, especially in plants. Hybrid zones are commonly located in regions across environmental gradients due to more opportunities to contact and ecological heterogeneity. For aquatic taxa, intrazonal character makes broad overlapping regions in intermediate environments between related species. However, we have limited information on the hybridization pattern of aquatic taxa in alpines, especially submerged macrophytes. In this study, we aimed to test the hypotheses that niche overlap and hybridization might be extensive in related aquatic plants across an altitudinal gradient. We evaluated the niche overlap in three related species pairs on the Qinghai-Tibetan Plateau and assessed the spatial pattern of hybrid populations. Obvious niche overlap and common hybridization were revealed in all three pairs of related aquatic plants. The plateau edge and river basins were broad areas for the sympatry of divergent taxa, where a large proportion of hybrid populations occurred. Hybrids are also discretely distributed in diverse habitats on the plateau. Differences in the extent of niche overlap, genetic incompatibility and phylogeographic history might lead to variation differences in hybridization patterns among the three species pairs. Our results suggested that plateau areas are a hotspot for ecologically divergent aquatic species to contact and mate and implied that hybridization may be important for the freshwater biodiversity of highlands.

Geographical and environmental contributions to genomic divergence in mangrove forests

Assessing the relative importance of geographical and environmental factors to the spatial distribution of genetic variation can provide information about the processes that maintain genetic variation in natural populations. With a globally wide but very restricted habitat distribution, mangrove trees are a useful model for studies aiming to understand the contributions of these factors. Mangroves occur along the continent–ocean interface of tropical and subtropical latitudes, regions considered inhospitable to many other types of plants. Here, we used landscape genomics approaches to investigate the relative contributions of geographical and environmental variables to the genetic variation of two black mangrove species, Avicennia schaueriana and Avicennia germinans, along the South American coast. Using single nucleotide polymorphisms, our results revealed an important role of ocean currents and geographical distance in the gene flow of A. schaueriana and an isolation-by-environment pattern in the organization of the genetic diversity of A. germinans. Additionally, for A. germinans, we observed significant correlations between genetic variation with evidence of selection and the influence of precipitation regimens, solar radiation and temperature patterns. These discoveries expand our knowledge about the evolution of mangrove trees and provide important information to predict future responses of coastal species to the expected global changes during this century.

Influence of environmental factors on the genetic variation of the aquatic macrophyte Ranunculus subrigidus on the Qinghai-Tibetan Plateau

BACKGROUND

Due to the environmental heterogeneity along elevation gradients, alpine ecosystems are ideal study objects for investigating how ecological variables shape the genetic patterns of natural species. The highest region in the world, the Qinghai-Tibetan Plateau, is a hotspot for the studies of evolutionary processes in plants. Many large rivers spring from the plateau, providing abundant habitats for aquatic and amphibious organisms. In the present study, we examined the genetic diversity of 13 Ranunculus subrigidus populations distributed throughout the plateau in order to elucidate the relative contribution of geographic distance and environmental dissimilarity to the spatial genetic pattern.

RESULTS

A relatively low level of genetic diversity within populations was found. No spatial genetic structure was suggested by the analyses of molecular variance, Bayesian clustering analysis and Mantel tests. Partial Mantel tests and multiple matrix regression analysis showed a significant influence of the environment on the genetic divergence of the species. Both climatic and water quality variables contribute to the habitat heterogeneity of R. subrigidus populations.

CONCLUSIONS

Our results suggest that historical processes involving long-distance dispersal and local adaptation may account for the genetic patterns of R. subrigidus and current environmental factors play an important role in the genetic differentiation and local adaptation of aquatic plants in alpine landscapes.

Bridging population genetics and the metacommunity perspective to unravel the biogeographic processes shaping genetic differentiation of Myriophyllum alterniflorum DC

The degree to which dispersal limitation interacts with environmental filtering has intrigued metacommunity ecologists and molecular biogeographers since the beginning of both research disciplines. Since genetic methods are superior to coarse proxies of dispersal, understanding how environmental and geographic factors influence population genetic structure is becoming a fundamental issue for population genetics and also one of the most challenging avenues for metacommunity ecology. In this study of the aquatic macrophyte Myriophyllum alterniflorum DC., we explored the spatial genetic variation of eleven populations from the Iberian Plateau by means of microsatellite loci, and examined if the results obtained through genetic methods match modern perspectives of metacommunity theory. To do this, we applied a combination of robust statistical routines including network analysis, causal modelling and multiple matrix regression with randomization. Our findings revealed that macrophyte populations clustered into genetic groups that mirrored their geographic distributions. Importantly, we found a significant correlation between genetic variation and geographic distance at the regional scale. By using effective (genetic) dispersal estimates, our results are broadly in line with recent findings from metacommunity theory and re-emphasize the need to go beyond the historically predominant paradigm of understanding environmental heterogeneity as the main force driving macrophyte diversity patterns.

What drives genetic and phenotypic divergence in the Red-crowned Ant tanager (Habia rubica, Aves: Cardinalidae), a polytypic species?

AIM

The effects of geographic and environmental variables on patterns of genetic and phenotypic differentiation have been thoroughly studied. Ecological speciation involves reproductive isolation due to divergent natural selection that can result in a positive correlation between genetic divergence and adaptive phenotypic divergence (isolation by adaptation, IBA). If the phenotypic target of selection is unknown or not easily measured, environmental variation can be used as a proxy, expecting positive correlation between genetic and environmental distances, independent of geographic distances (isolation by environment, IBE). The null model is that the amount of gene flow between populations decreases as the geographic distance between them increases, and genetic divergence is due simply to the neutral effects of genetic drift (isolation by distance, IBD). However, since phenotypic differentiation in natural populations may be autocorrelated with geographic distance, it is often difficult to distinguish IBA from the neutral expectation of IBD. In this work, we test hypotheses of IBA, IBE, and IBD in the Red-crowned Ant tanager (Habia rubica).

LOCATION

Mesoamerica (Mexico-Central America) and South America.

TAXON

Habia rubica (Aves: Cardinalidae).

METHODS

We compiled genetic data, coloration, and morphometric data from specimens from collections in Mexico and the United States. We used the Multiple Matrix Regression with Randomization (MMRR) approach to evaluate the influence of geographic and environmental distances on genetic and phenotypic differentiation of H. rubica at both phylogroup and population levels.

RESULTS

Our results provide strong evidence that geographic distance is the main driver of genetic variation in H. rubica. We did not find evidence that climate variation is driving population differentiation in this species across a widespread geographic region.

MAIN CONCLUSIONS

Our data point to geographic isolation as the main factor structuring genetic variation within populations of H. rubica and suggest that climate is not playing a major role in genetic differentiation within this species.

Does intraspecific variability matter in ecological risk assessment? Investigation of genotypic variations in three macrophyte species exposed to copper

To limit anthropogenic impact on ecosystems, regulations have been implemented along with global awareness that human activities are harmful to the environment. Ecological risk assessment (ERA) is the main procedure which allows to assess potential impacts of stressors on the environment as a result of human activities. ERA is typically implemented through different steps of laboratory testing. The approaches taken for ERA evolve along with scientific knowledge, to improve predictions on ecological risks for ecosystems. We here address the importance of intraspecific variability as a potential source of error in the laboratory evaluation of pollutants. To answer this question, three aquatic macrophyte species with different life-history traits but with their leaves directly in contact with the water were chosen; Lemna minor and Myriophyllum spicatum, two OECD model species, and Ceratophyllum demersum. For each species, three or four genotypes were exposed to 7-8 copper concentrations (up to 1.9 mg/L, 2 mg/L or 36 mg/L for C. demersum, L. minor and M. spicatum, respectively). To assess species sensitivity, growth-related endpoints such as Relative Growth Rate (RGR), based either on biomass production or on length/frond production, and chlorophyll fluorescence F_v/F_m, were measured. For each endpoint, the effective concentration 50% (EC₅₀) was calculated. Almost all endpoints were affected by Cu exposure, except F_v/F_m of M. spicatum, and resulted in significant differences among genotypes for Cu sensitivity. Genotypes of L. minor exhibited up to 35% of variation in EC50 values based on F_v/F_m, showing differential sensivity among genotypes. Significant differences in EC₅₀ values were found for RGR based on length for M. spicatum, with up to 72% of variation. Finally, C. demersum demonstrated significant sensitivity differences among genotypes with up to 78% variation for EC₅₀ based on length. Overall, interspecific variation was higher than intraspecific variation, and explained 77% of the variation found among genotypes for RGR based on biomass, and 99% of the variation found for F_v/F_m. Our results highlight that depending on the endpoint, sensitivity can vary greatly within a species, and that pollutant- and species-specific endpoints should be considered in ERA.

Genetic diversity and structure of Elymus tangutorum accessions from western China as unraveled by AFLP markers

BACKGROUND

Understanding genetic diversity of wild plant germplasm and the relationships between ecogeographic and genetic characteristics may provide insights for better utilizing and conserving genetic resources. Elymus tangutorum (Nevski) Hand.-Mazz, a cool-season hexaploid perennial, is an important pasture bunchgrass species used for forages and grassland restoration in Qinghai-Tibet Plateau and northwest China. In this study, 27 E. tangutorum accessions from diverse origins of western China were evaluated using AFLP markers in an effort to delve into the genetic relationships among them. The effects of eco-environmental factors and geographical isolation on the genetic diversity and population structure were also elucidated.

RESULTS

On account of 554 polymorphic fragments amplified with 14 primer combinations, the mean values of some marker parameters including polymorphic information content, resolving power and marker index were 0.2504, 14.10 and 23.07, respectively, validating the high efficiency and reliability of the markers selected. Genetic dissimilarity index values among accessions ranged from 0.1024 to 0.7137 with a mean of 0.2773. STRUCTURE, UPGMA clustering and PCoA analyses showed that all accessions could be divided into the three main clusters; however, this results do not exactly coincide with geographic groups. We found medium differentiation (F ST  = 0.162) between Qinghai-Tibet Plateau (QTP) and Xinjiang (XJC), and high differentiation (F ST  = 0.188) among three Bayesian subgroups. A significant correlation (r = 0.312) between genetic and geographical distance was observed by Mantel test in the species level, while the weak correlation was detected between genetic and environmental distance for all accessions and most of geographical groups. In addition, a significant ecological influence of average annual precipitation on genetic distance was revealed in XJC group and the Bayesian subgroup A.

CONCLUSION

This study indicates that AFLP technique are a useful tool to measure genetic diversity in E. tangutorum, showing that geographical and environmental factors (especially precipitation) together, play a crucial role in genetic differentiation patterns. These findings underline the importance of local adaptation in shaping patterns of genetic variability and population structure in E. tangutorum germplasm collected in Western China.

Carbon Gain Limitation Is the Primary Mechanism for the Elevational Distribution Limit of Myriophyllum in the High-Altitude Plateau

Temperature comprises a major driver for species distribution and physiological processes in alpine plants. For all terrestrial plant species tested to date, elevation associated decreases in temperature have been observed to influence the balance between carbon acquisition and usage; restricting the upper limit of most alpine trees (i.e., treeline). However, such a carbon source-sink balance has not been tested in any alpine aquatic plants, which is an important component of the alpine aquatic ecosystem. The Myriophyllum species inhabits a broad range of habitats across the high-altitude plateau. Three Myriophyllum species (Myriophyllum spicatum, Myriophyllum verticillatum, and Myriophyllum sibiricum) from 12 water bodies at elevational gradients between 2766 and 5111 m were collected in the Qinghai-Tibetan Plateau. The late growing seasonal concentrations of non-structural carbohydrates (NSC) in the leaves were measured to find how high-altitude conditions influence the carbon balance in aquatic plants. Regression tree analysis separated the 12 water bodies into two groups according to water turbidity (seven water bodies with high turbidity and five water bodies with low turbidity). Overall, leaf NSC concentrations (primarily starch) decreased significantly with increasing elevation in widely distributed M. spicatum and M. verticillatum. Regression tree analysis indicated that water turbidity (i.e., shady environment) was a strong determinant of leaf NSC. In the low turbidity group (<3.5 NTU), leaf NSC concentrations decreased with increasing elevation; however, in the high turbidity group (>3.5 NTU), leaf NSC concentrations were low and had no association with elevation. Unlike most recent studies in tree species, which show low temperatures limited growth at high-elevations, our results demonstrated that carbon gain limitation is the primary mechanism for the elevational distribution limit of Myriophyllum species in the Qinghai-Tibetan Plateau. Moreover, water turbidity moderated the effects of low temperature by masking the expected carbon limitation trend. Therefore, at least two environmental factors (i.e., temperature and light availability) induced photosynthesis decreases might explain the NSC responses for aquatic plants in response to elevation.

Living in two worlds: Evolutionary mechanisms act differently in the native and introduced ranges of an invasive plant

Identifying the factors that influence spatial genetic structure among populations can provide insights into the evolution of invasive plants. In this study, we used the common reed (Phragmites australis), a grass native in Europe and invading North America, to examine the relative importance of geographic, environmental (represented by climate here), and human effects on population genetic structure and its changes during invasion. We collected samples of P. australis from both the invaded North American and native European ranges and used molecular markers to investigate the population genetic structure within and between ranges. We used path analysis to identify the contributions of each of the three factors-geographic, environmental, and human-related-to the formation of spatial genetic patterns. Genetic differentiation was observed between the introduced and native populations, and their genetic structure in the native and introduced ranges was different. There were strong effects of geography and environment on the genetic structure of populations in the native range, but the human-related factors manifested through colonization of anthropogenic habitats in the introduced range counteracted the effects of environment. The between-range genetic differences among populations were mainly explained by the heterogeneous environment between the ranges, with the coefficient 2.6 times higher for the environment than that explained by the geographic distance. Human activities were the primary contributor to the genetic structure of the introduced populations. The significant environmental divergence between ranges and the strong contribution of human activities to the genetic structure in the introduced range suggest that invasive populations of P. australis have evolved to adapt to a different climate and to human-made habitats in North America.

Isolation of polymorphic microsatellite loci in the New Zealand endemic sand-binder, Ficinia spiralis (Cyperaceae)

PREMISE OF THE STUDY

Ficinia spiralis (Cyperaceae) is a declining sand-binding sedge of ecological and cultural importance. Microsatellite primers were developed in F. spiralis to investigate how population genetic structure is related to the pronounced morphological, physiological, and ecological variation observed in this species.

METHODS AND RESULTS

A 454 shotgun-sequencing approach was used to generate 157,274 raw sequence reads, 536 of which contained microsatellites. After initial primer testing for 40 loci, 14 polymorphic loci were isolated, containing five to 27 alleles per locus. Ten of these loci also amplified in a congener, F. nodosa.

CONCLUSIONS

These loci will enable the assessment of the population genetic structure of F. spiralis, improving our understanding of the population processes underlying the observed morphological, physiological, and ecological variation in this endemic species. As the first microsatellites developed in Ficinia, these loci are a valuable resource for population genetic studies within this genus.

Population genetic structure in six sympatric and widespread aquatic plants inhabiting diverse lake environments in China

Many aquatic plant species are distributed over large areas and diverse environments with populations interconnected by abiotic and biotic mediators. Here, we examined differences and similarities in the population genetic structure of six sympatric and widespread aquatic plant species. We sampled the aquatic species from six Chinese lakes found on plateaus, plains, and different river systems and analyzed them using inter‐simple sequence repeat (ISSR) markers. Samples originating from each lake tended to cluster together. Of the six species, only Nymphoides peltata and Myriophyllum spicatum could be divided into plateau and plain groups, once Taihu Lake individuals were excluded. Genetic similarities between populations connected by the Yangtze River were not consistently higher than unconnected populations. Populations from Taihu Lake and/or Weishanhu Lake were distant from other lake populations for all species except Potamogeton lucens. The Taihu and Weishanhu populations clustered for Ceratophyllum demersum and Typha latifolia. Hydrophilous C. demersum had the lowest gene flow (Nm = 0.913), whereas the entomophilous Hydrocharis dubia (Nm = 2.084) and N. peltata (Nm = 2.204) had the highest gene flow. The genetic relationships among distant populations of aquatic plants reflect the comprehensive effects of environmental selection pressure and biotic and abiotic connectivity. Differences in environmental factors between plateau and plain lakes and long distance hydrochory have limited importance on aquatic plant genetic structures. Among multiple evolutionary forces, gene flow mediated by birds may play the most important role in the formation of genetic patterns in the six species examined. For example, the close genetic relationship between Taihu Lake and Weishanhu Lake populations, each in different river systems and with different climates, may be related to the migration routes of birds. Differences in gene flow among the six aquatic plants may be attributable to different bird‐transport and the fruit traits of each species.

Strong Genetic Differentiation of Submerged Plant Populations across Mountain Ranges: Evidence from Potamogeton pectinatus in Iran

Biogeographic barriers for freshwater biota can be effective at various spatial scales. At the largest spatial scale, freshwater organisms can become genetically isolated by their high mountain ranges, vast deserts, and inability to cross oceans. Isolation by distance of aquatic plants is expected to be stronger across than alongside mountain ridges whereas the heterogeneity of habitats among populations and temporary droughts may influence connectivity and hamper dispersal. Suitable aquatic plant habitats became reduced, even for the widespread submerged Potamogeton pectinatus L. (also named Stuckenia pectinata) giving structure to various aquatic habitats. We compared the level of genetic diversity in a heterogeneous series of aquatic habitats across Iran and tested their differentiation over distances and across mountain ranges (Alborz and Zagros) and desert zones (Kavir), with values obtained from temperate region populations. The diversity of aquatic ecosystems across and along large geographic barriers provided a unique ecological situation within Iran. P. pectinatus were considered from thirty-six sites across Iran at direct flight distances ranging from 20 to 1,200 km. Nine microsatellite loci revealed a very high number of alleles over all sites. A PCoA, NJT clustering and STRUCTURE analysis revealed a separate grouping of individuals of southeastern Iranian sites and was confirmed by their different nuclear ITS and cpDNA haplotypes thereby indicating an evolutionary significant unit (ESU). At the level of populations, a positive correlation between allelic differentiation Dest with geographic distance was found. Individual-based STRUCTURE analysis over 36 sites showed 7 genetic clusters. FST and RST values for ten populations reached 0.343 and 0.521, respectively thereby indicating that allele length differences are more important and contain evolutionary information. Overall, higher levels of diversity and a stronger differentiation was revealed among Iranian P. pectinatus than previously observed for temperate European regions, due to regional differences across mountain ranges over long distances.

Genetic and geographical structure of boreal plants in their southern range: phylogeography of Hippuris vulgaris in China

BACKGROUND

Our current understanding of the evolutionary history of boreal and arctic-alpine plants in their southern range in Asia remains relatively poor. Using three cpDNA non-coding regions and nine nuclear microsatellite (nSSR) loci, we examine the phylogeographic pattern in a broad geographic sampling of the boreal plant Hippuris vulgaris to infer its dispersal and diversification in China. In addition, the species distributions at the Last Glacial Maximum (LGM) and at present were predicted using ecological niche modeling (ENM).

RESULTS

The cpDNA results revealed two distinct lineages, A and B. A is restricted to Northeast China; B is distributed in Northwest China, the Qinghai-Tibet Plateau (QTP) and North and Northeast (NNE) China; and A and B diverged ca. 1.36 Ma. The nSSR data revealed two genetic clusters corresponding to the two cpDNA lineages and nonreciprocal hybridization with lineage A as the maternal lineage in Northeast China. Cluster B further divided into three subclusters: I, mainly in NNE China and the northeastern border of the QTP; II, in Northwest China and the QTP; and III, on the QTP. ENM predicted a marked range shift on the QTP at the LGM, retreating from the platform to the northeast and southeast edges.

CONCLUSIONS

Hippuris vulgaris probably diverged into lineages A and B in high latitudes and then immigrated into Northeast China and Northwest China, respectively. Lineage A persisted and diversified in Northeast China. Lineage B reached the QTP during the mid-Pleistocene, diversified in that region due to the influence of climatic oscillations, migrated into Northeast China and subsequently hybridized with lineage A. Our findings give empirical evidence that boreal plants display complex evolutionary history in their southern range in Asia and provide new insights into the evolution of boreal and arctic-alpine plants.