Genetic roadmap of the Arctic: plant dispersal highways, traffic barriers and capitals of diversity

Parallel patterns of genetic diversity and structure in circumboreal species of the Sphagnum capillifolium complex

PREMISE

Shared geographical patterns of population genetic variation among related species is a powerful means to identify the historical events that drive diversification. The Sphagnum capillifolium complex is a group of closely related peat mosses within the Sphagnum subgenus Acutifolia and contains several circumboreal species whose ranges encompass both glaciated and unglaciated regions across the northern hemisphere. In this paper, we (1) inferred the phylogeny of subg. Acutifolia and (2) investigated patterns of population structure and genetic diversity among five circumboreal species within the S. capillifolium complex.

METHODS

We generated RAD sequencing data from most species of the subg. Acutifolia and samples from across the distribution ranges of circumboreal species within the S. capillifolium complex.

RESULTS

We resolved at least 14 phylogenetic clusters within the S. capillifolium complex. Five circumboreal species show some common patterns: One population system comprises plants in eastern North America and Europe, and another comprises plants in the Pacific Northwest or around the Beringian and Arctic regions. Alaska appears to be a hotspot for genetic admixture, genetic diversity, and sometimes endemic subclades.

CONCLUSIONS

Our results support the hypothesis that populations of five circumboreal species within the S. capillifolium complex survived in multiple refugia during the last glacial maximum. Long-distance dispersal out of refugia, population bottlenecks, and possible adaptations to conditions unique to each refugium could have contributed to current geographic patterns. These results indicate the important role of historical events in shaping the complex population structure of plants with broad distribution ranges.

Unveiling the evolutionary history of lingonberry (Vaccinium vitis-idaea L.) through genome sequencing and assembly of European and North American subspecies

Lingonberry (Vaccinium vitis-idaea L.) produces tiny red berries that are tart and nutty in flavor. It grows widely in the circumpolar region, including Scandinavia, northern parts of Eurasia, Alaska, and Canada. Although cultivation is currently limited, the plant has a long history of cultural use among indigenous communities. Given its potential as a food source, genomic resources for lingonberry are significantly lacking. To advance genomic knowledge, the genomes for 2 subspecies of lingonberry (V. vitis-idaea ssp. minus and ssp. vitis-idaea var. 'Red Candy') were sequenced and de novo assembled into contig-level assemblies. The assemblies were scaffolded using the bilberry genome (Vaccinium myrtillus) to generate a chromosome-anchored reference genome consisting of 12 chromosomes each with a total length of 548.07 Mb [contig N50 = 1.17 Mb, BUSCO (C%) = 96.5%] for ssp. vitis-idaea and 518.70 Mb [contig N50 = 1.40 Mb, BUSCO (C%) = 96.9%] for ssp. minus. RNA-seq-based gene annotation identified 27,243 and 25,718 genes on the respective assembly, and transposable element detection methods found that 45.82 and 44.58% of the genome were repeats. Phylogenetic analysis confirmed that lingonberry was most closely related to bilberry and was more closely related to blueberries than cranberries. Estimates of past effective population size suggested a continuous decline over the past 1-3 MYA, possibly due to the impacts of repeated glacial cycles during the Pleistocene leading to frequent population fragmentation. The genomic resource created in this study can be used to identify industry-relevant genes (e.g. anthocyanin production), infer phylogeny, and call sequence-level variants (e.g. SNPs) in future research.

The Perspective of Arctic-Alpine Species in Southernmost Localities: The Example of Kalmia procumbens in the Pyrenees and Carpathians

High-mountain and arctic plants are considered especially sensitive to climate change because of their close adaptation to the cold environment. Kalmia procumbens, a typical arctic-alpine species, reaches southernmost European localities in the Pyrenees and Carpathians. The aim of this study was the assessment and comparison of the current potential niche areas of K. procumbens in the Pyrenees and Carpathians and their possible reduction due to climate change, depending on the scenario. The realized niches of K. procumbens in the Pyrenees are compact, while those in the Carpathians are dispersed. In both mountain chains, the species occurs in the alpine and subalpine vegetation belts, going down to elevations of about 1500-1600 m, while the most elevated localities in the Pyrenees are at ca. 3000 m, about 500 m higher than those in the Carpathians. The localities of K. procumbens in the Carpathians have a more continental climate than those in the Pyrenees, with lower precipitation and temperatures but higher seasonality of temperature and precipitation. The species covered a larger area of geographic range during the Last Glacial Maximum, but its geographic range was reduced during the mid-Holocene. Due to climate warming, a reduction in the potential area of occurrence could be expected in 2100; this reduction is expected to be strong in the Carpathians and moderate in the Pyrenees.

Beringia as a high-latitude engine of avian speciation

Beringia is a biogeographically dynamic region that extends from northeastern Asia into northwestern North America. This region has affected avian divergence and speciation in three important ways: (i) by serving as a route for intercontinental colonisation between Asia and the Americas; (ii) by cyclically splitting (and often reuniting) populations, subspecies, and species between these continents; and (iii) by providing isolated refugia through glacial cycles. The effects of these processes can be seen in taxonomic splits of shallow to increasing depths and in the presence of regional endemics. We review the taxa involved in the latter two processes (splitting-reuniting and isolation), with a focus on three research topics: avian diversity, time estimates of the generation of that diversity, and the regions within Beringia that might have been especially important. We find that these processes have generated substantial amounts of avian diversity, including 49 pairs of avian subspecies or species whose breeding distributions largely replace one another across the divide between the Old World and the New World in Beringia, and 103 avian species and subspecies endemic to this region. Among endemics, about one in three is recognised as a full biological species. Endemic taxa in the orders Charadriiformes (shorebirds, alcids, gulls, and terns) and Passeriformes (perching birds) are particularly well represented, although they show very different levels of diversity through evolutionary time. Endemic Beringian Charadriiformes have a 1.31:1 ratio of species to subspecies. In Passeriformes, endemic taxa have a 0.09:1 species-to-subspecies ratio, suggesting that passerine (and thus terrestrial) endemism might be more prone to long-term extinction in this region, although such 'losses' could occur through their being reconnected with wider continental populations during favourable climatic cycles (e.g. subspecies reintegration with other populations). Genetic evidence suggests that most Beringian avian taxa originated over the past 3 million years, confirming the importance of Quaternary processes. There seems to be no obvious clustering in their formation through time, although there might be temporal gaps with lower rates of diversity generation. For at least 62 species, taxonomically undifferentiated populations occupy this region, providing ample potential for future evolutionary diversification.

From everywhere all at once: Several colonization routes available to Svalbard in the early Holocene

For many arctic species, the spatial (re-)colonization patterns after the last Pleistocene glaciation have been described. However, the temporal aspects of their colonization are largely missing. Did one route prevail early, while another was more important later? The high Arctic archipelago Svalbard represents a good model system to address timeframe of postglacial plant colonization. Svalbard was almost fully glaciated during last glacial maximum and (re-)colonization of vascular plants began in early Holocene. Early Holocene climatic optimum (HCO) supported an expanded establishment of a partly thermophilic vegetation. Today, we find remnants of this vegetation in sheltered regions referred to as "Arctic biodiversity hotspots". The oldest record of postglacial plant colonization to Svalbard is found in Ringhorndalen-Flatøyrdalen. Even though thermophilic species could establish also later in Holocene, only HCO was favorable for vast colonization, and only hotspots offered stable conditions for thermophilic populations throughout Holocene. Thus, these relic populations may reflect colonization patterns of HCO. We investigate whether the colonization direction of thermophilic plants (Arnica angustifolia, Campanula uniflora, Pinguicula alpina, Tofieldia pusilla, and Vaccinium uliginosum ssp. microphyllum) in Ringhorndalen-Flatøyrdalen was uniform and different from later colonization events in other localities and non-thermophilic plants (Arenaria humifusa, Bistorta vivipara, Juncus biglumis, Oxyria digyna, and Silene acaulis). We analyzed plastid haplotypes of the 10 taxa from Ringhorndalen-Flatøyrdalen, from later-colonized localities in Svalbard, and from putative source regions outside Svalbard. Only rare and thermophilic taxa Campanula uniflora and Vaccinium uliginosum ssp. microphyllum provided results suggesting at least two colonization events from different source regions. Tofieldia pusilla and all the non-thermophilic plants showed no clear phylogeographically differentiation within Svalbard. Two of the thermophilic species showed no sequence variation. Based on the results, a uniform colonization direction to Svalbard in early Holocene is not probable; several source areas and dispersal directions were contemporarily involved.

Genomic evidence for contrasting patterns of host-associated genetic differentiation across shared host-plant species in leaf- and bud-galling sawflies

Resource specialization and ecological speciation arising through host-associated genetic differentiation (HAD) are frequently invoked as an explanation for the high diversity of plant-feeding insects and other organisms with a parasitic lifestyle. While genetic studies have demonstrated numerous examples of HAD in insect herbivores, the rarity of comparative studies means that we still lack an understanding of how deterministic HAD is, and whether patterns of host shifts can be predicted over evolutionary timescales. We applied genome-wide single nucleotide polymorphism and mitochondrial DNA sequence data obtained through genome resequencing to define species limits and to compare host-plant use in population samples of leaf- and bud-galling sawflies (Hymenoptera: Tenthredinidae: Nematinae) collected from seven shared willow (Salicaceae: Salix) host species. To infer the repeatability of long-term cophylogenetic patterns, we also contrasted the phylogenies of the two galler groups with each other as well as with the phylogeny of their Salix hosts estimated based on RADseq data. We found clear evidence for host specialization and HAD in both of the focal galler groups, but also that leaf gallers are more specialized to single host species compared with most bud gallers. In contrast to bud gallers, leaf gallers also exhibited statistically significant cophylogenetic signal with their Salix hosts. The observed discordant patterns of resource specialization and host shifts in two related galler groups that have radiated in parallel across a shared resource base indicate a lack of evolutionary repeatability in the focal system, and suggest that short- and long-term host use and ecological diversification in plant-feeding insects are dominated by stochasticity and/or lineage-specific effects.

Clear phylogeographical structures shed light on the origin and dispersal of the aquatic boreal plant Hippuris vulgaris

Aquatic plants are an important ecological group in the arctic flora; however, their evolutionary histories remain largely unknown. In order to deepen our understanding of the evolution of these plants, we explored the phylogeographical structure of an aquatic boreal plant Hippuris vulgaris in a broad geographical sampling from Eurasia and North America using the chloroplast intergenic spacer psbA-trnH and seven nuclear microsatellite loci. Two closely-related species H. lanceolata and H. tetraphylla were also included because of their taxonomic controversy. Both chloroplast DNA sequences and nuclear microsatellite data revealed three genetic lineages with distinct distribution ranges. Incongruence between nuclear and chloroplast DNA lineages occurred in 14 samples from Russian Far East and Europe caused by inter-lineage hybridization. No private haplotypes or independent genetic clusters were evident in H. lanceolata or H. tetraphylla, suggesting that these two species should be considered conspecific ecotypes of H. vulgaris. Analysis using Approximate Bayesian Computation-Random Forest approach suggests that Hippuris vulgaris originated in China, followed by dispersal into Russia plus Northeast China, then successively westwards into Europe and North America, and finally into the Russian Far East from both North America and Russia plus Northeast China. This study is the first to elucidate the historical dispersal processes of a circumarctic aquatic plant across the entirety of its range.

Landscape Genomics Provides Evidence of Ecotypic Adaptation and a Barrier to Gene Flow at Treeline for the Arctic Foundation Species Eriophorum vaginatum

Global climate change has resulted in geographic range shifts of flora and fauna at a global scale. Extreme environments, like the Arctic, are seeing some of the most pronounced changes. This region covers 14% of the Earth's land area, and while many arctic species are widespread, understanding ecotypic variation at the genomic level will be important for elucidating how range shifts will affect ecological processes. Tussock cottongrass (Eriophorum vaginatum L.) is a foundation species of the moist acidic tundra, whose potential decline due to competition from shrubs may affect ecosystem stability in the Arctic. We used double-digest Restriction Site-Associated DNA sequencing to identify genomic variation in 273 individuals of E. vaginatum from 17 sites along a latitudinal gradient in north central Alaska. These sites have been part of 30 + years of ecological research and are inclusive of a region that was part of the Beringian refugium. The data analyses included genomic population structure, demographic models, and genotype by environment association. Genome-wide SNP investigation revealed environmentally associated variation and population structure across the sampled range of E. vaginatum, including a genetic break between populations north and south of treeline. This structure is likely the result of subrefugial isolation, contemporary isolation by resistance, and adaptation. Forty-five candidate loci were identified with genotype-environment association (GEA) analyses, with most identified genes related to abiotic stress. Our results support a hypothesis of limited gene flow based on spatial and environmental factors for E. vaginatum, which in combination with life history traits could limit range expansion of southern ecotypes northward as the tundra warms. This has implications for lower competitive attributes of northern plants of this foundation species likely resulting in changes in ecosystem productivity.

Decades-long phylogeographic issues: complex historical processes and ecological factors on genetic structure of alpine plants in the Japanese Archipelago

Mountain regions are important places for biodiversity, where organisms could persist throughout prolonged periods and accumulate genetic divergence as well as promote speciation. Roles of mountains for biodiversity have been exclusively discussed in regions that have specifically diverse species or covered with ice-sheets during the Pleistocene glacial periods, whereas the importance of mountainous regions in East Asia has been less disputed. High mountains in the Japanese Archipelago, located at the eastern edge of the Eurasia continent, have one of southernmost populations of alpine and arctic-alpine plants that are also distributed in the northern Pacific and/or the circumarctic regions. Phylogeographic studies on the Japanese alpine plants have excluded their possible ephemeral occurrence during the current warm period, and rather, suggest persistence of alpine plants throughout several cycles of climate changes in the Pleistocene on high mountains in central Honshu, the main island of the Japanese Archipelago. In this review, I look through decade long phylogeographic studies and show complicated patterns of range dynamics of Japanese alpine plants. In addition, I note recent findings of genetic relationships of Japanese populations of alpine and/or arctic-alpine plants with those in northern regions and their possible ecological divergence in the Japanese Archipelago. Taken together, I provide several issues for understanding historical processes that established distribution of alpine plants following climate changes as well as their diversification and propose importance of Japanese populations of alpine plants on biodiversity in alpine communities across broader range, especially in the northern Pacific region.

Rapid evolution of post-zygotic reproductive isolation is widespread in Arctic plant lineages

BACKGROUND AND AIMS

The Arctic tundra, with its extreme temperatures and short growing season, is evolutionarily young and harbours one of the most species-poor floras on Earth. Arctic species often show little phenotypic and genetic divergence across circumpolar ranges. However, strong intraspecific post-zygotic reproductive isolation (RI) in terms of hybrid sterility has frequently evolved within selfing Arctic species of the genus Draba. Here we assess whether incipient biological species are common in the Arctic flora.

METHODS

We conducted an extensive crossing experiment including six species representing four phylogenetically distant families collected across the circumpolar Arctic. We crossed conspecific parental populations representing different spatial scales, raised 740 F1 hybrids to maturity and measured fertility under laboratory conditions. We examined genetic divergence between populations for two of these species (Cardamine bellidifolia and Ranunculus pygmaeus).

KEY RESULTS

In five of the six species, we find extensive reduction in pollen fertility and seed set in F1 hybrids; 219 (46 %) of the 477 F1 hybrids generated between parents separated by ≥427 km had <20 % pollen fertility. Isolation with migration (IM) and *BEAST analyses of sequences of eight nuclear genes in C. bellidifolia suggests that reproductively isolated populations of this species diverged during, or even after, the last glaciation. Likewise, Arctic populations of R. pygmaeus were genetically very similar despite exhibiting strongly reduced fertility in crosses, suggesting that RI evolved recently also in this species.

CONCLUSION

We show that post-zygotic RI has developed multiple times within taxonomically recognized Arctic species belonging to several distantly related lineages, and that RI may have developed over just a few millennia. Rapid and widespread evolution of incipient biological species in the Arctic flora might be associated with frequent bottlenecks due to glacial cycles, and/or selfing mating systems, which are common in the harsh Arctic environment where pollinators are scarce.

Climate-Change Impacts on the Southernmost Mediterranean Arctic-Alpine Plant Populations

Human-induced climate- and land-use change have been affecting biogeographical and biodiversity patterns for the past two centuries all over the globe, resulting in increased extinction and biotic homogenization rates. High mountain ecosystems are more sensitive to these changes, which have led to physiological and phenological shifts, as well as to ecosystem processes’ deformation. Glacial relicts, such as arctic-alpine taxa, are sensitive indicators of the effects of global warming and their rear-edge populations could include warm-adapted genotypes that might prove—conservation-wise—useful in an era of unprecedented climate regimes. Despite the ongoing thermophilization in European and Mediterranean summits, it still remains unknown how past and future climate-change might affect the distributional patterns of the glacial relict, arctic-alpine taxa occurring in Greece, their European southernmost distributional limit. Using species distribution models, we investigated the impacts of past and future climate changes on the arctic-alpine taxa occurring in Greece and identified the areas comprising arctic-alpine biodiversity hotspots in Greece. Most of these species will be faced with severe range reductions in the near future, despite their innate resilience to a multitude of threats, while the species richness hotspots will experience both altitudinal and latitudinal shifts. Being long-lived perennials means that there might be an extinction-debt present in these taxa, and a prolonged stability phase could be masking the deleterious effects of climate change on them. Several ex situ conservation measures (e.g., seed collection, population augmentation) should be taken to preserve the southernmost populations of these rare arctic-alpine taxa and a better understanding of their population genetics is urgently needed.

Genetic diversity of Salixlapponum populations in Central Europe

Salixlapponum is a cold-tolerant relict species in Europe that occurs in several sites, probably reflecting previous migration routes of S.lapponum during the Pleistocene. However, only a few data are available on the genetic structures of populations of S.lapponum. In this study, we use PCR-ISSR markers to investigate genetic variation in 19 European populations of S.lapponum L. AMOVA analysis shows that most of the variation (55.8%) occurs within populations; variability among groups accounts for 19.7%. An AMOVA analysis based on four groups determined by STRUCTURE analysis shows similar results: variability of 54.1% within the population and variability of 18.9% between the four population groups, based on geographic regions. Within individual geographic groups, which are characterised by the studied populations, the lowest variability (as well as the highest homogeneity) was found in populations located in Belarus. The obtained results are consistent with our expectations that the European Lowland could be a significant geographic barrier for gene flow over large geographic distances for S.lapponum. Both the Scandinavian and Belarusian populations, as well as those coming from NE Poland, are characterised by significant genetic distinctiveness. However, some populations from NE Poland and the Sudetes show similarities with populations from other geographic regions, indicating existing genetic relationships between them. Moreover, the results suggest a fairly clear division of the population into 4 emerging geographic regions, although separated by a geographical barrier: the Polish lowland, which forms part of the larger geographic unit known as the European Lowland.

Non-linear genetic diversity and notable population differentiation caused by low gene flow of bermudagrass [Cynodon dactylon (L.) Pers.] along longitude gradients

Background

Environmental variation related to ecological habitat is the main driver of plant adaptive divergence. Longitude plays an important role in the formation of plant population structure, indicating that environmental differentiation can significantly shape population structure.

Methods

Genetic diversity and population genetic structure were estimated using 105 expressed sequence tag-derived simple sequence repeat (EST-SSR) loci. A total of 249 C. dactylon (L.) Pers. (common bermudagrass) individuals were sampled from 13 geographic sites along the longitude (105°57′34″–119°27′06″E).

Results

There was no obvious linear trend of intra-population genetic diversity along longitude and the intra-population genetic diversity was not related to climate in this study. Low gene flow (Nm = 0.7701) meant a rich genetic differentiation among populations of C. dactylon along longitude gradients. Significantly positive Mantel correlation (r = 0.438, P = 0.001) was found between genetic distance and geographical interval while no significant partial Mantel correlation after controlling the effect of mean annual precipitation, which indicated geographic distance correlated with mean annual precipitation affect genetic distance. The genetic diversity of C. dactylon with higher ploidy level was higher than that with lower ploidy level and groups of individuals with higher ploidy level were separated further away by genetic distance from the lower ploidy levels. Understanding the different genetic bases of local adaptation comparatively between latitude and longitude is one of the core findings in the adaptive evolution of plants.

Ecotypic differentiation of a circumpolar Arctic-alpine species at mid-latitudes: variations in the ploidy level and reproductive system of Vaccinium vitis-idaea

Although plant species originated from Arctic regions commonly grow in alpine habitats at mid-latitudes, some populations of these species exist also in some specific habitats below the treeline. Local populations at lower elevations may have different origins, ploidy levels, mating systems and/or morphological traits from alpine populations, but comparative studies between alpine and low-elevation populations are scarce. We aimed to reveal the ecological and genetic differentiations between higher and lower populations of Vaccinium vitis-idaea in Hokkaido, northern Japan by comparing 22 populations growing in diverse environments. We analysed the ploidy level of individual populations using flow cytometry. Genetic differentiation among populations, and genetic diversity within populations were calculated using microsatellite markers. Fruit and seed production were recorded under natural conditions, and a pollination experiment was conducted to reveal the variations in mating system across populations. Furthermore, we compared shoot growth and leaf characteristics among populations. Most of the low-elevation populations were tetraploid, whereas all but one of the alpine populations were diploid. Tetraploid populations were clearly differentiated from diploid populations. Some tetraploid populations formed huge clonal patches but genetic diversity was higher in tetraploids than in diploids. Alpine diploids were self-incompatible and produced more seeds per fruit than tetraploid populations. In contrast, tetraploids showed high self-compatibility. Leaf size and foliar production were greater in tetraploid populations. Our results indicate that the genetic compositions of low-elevation tetraploid populations are different from those of alpine diploid populations. Most populations at lower elevations contained unique ecotypes suited to persistence in isolated situations. Local, low-elevation populations of typical alpine species maintain ecologically and genetically specific characteristics and could be valuable in terms of evolutionary and conservation biology. The present study demonstrates the biological importance of small and isolated populations at the edges of species distribution.

Holocene chloroplast genetic variation of shrubs (Alnus alnobetula, Betula nana, Salix sp.) at the siberian tundra-taiga ecotone inferred from modern chloroplast genome assembly and sedimentary ancient DNA analyses

Climate warming alters plant composition and population dynamics of arctic ecosystems. In particular, an increase in relative abundance and cover of deciduous shrub species (shrubification) has been recorded. We inferred genetic variation of common shrub species (Alnus alnobetula, Betula nana, Salix sp.) through time. Chloroplast genomes were assembled from modern plants (n = 15) from the Siberian forest-tundra ecotone. Sedimentary ancient DNA (sedaDNA; n = 4) was retrieved from a lake on the southern Taymyr Peninsula and analyzed by metagenomics shotgun sequencing and a hybridization capture approach. For A. alnobetula, analyses of modern DNA showed low intraspecies genetic variability and a clear geographical structure in haplotype distribution. In contrast, B. nana showed high intraspecies genetic diversity and weak geographical structure. Analyses of sedaDNA revealed a decreasing relative abundance of Alnus since 5,400 cal yr BP, whereas Betula and Salix increased. A comparison between genetic variations identified in modern DNA and sedaDNA showed that Alnus variants were maintained over the last 6,700 years in the Taymyr region. In accordance with modern individuals, the variants retrieved from Betula and Salix sedaDNA showed higher genetic diversity. The success of the hybridization capture in retrieving diverged sequences demonstrates the high potential for future studies of plant biodiversity as well as specific genetic variation on ancient DNA from lake sediments. Overall, our results suggest that shrubification has species-specific trajectories. The low genetic diversity in A. alnobetula suggests a local population recruitment and growth response of the already present communities, whereas the higher genetic variability and lack of geographical structure in B. nana may indicate a recruitment from different populations due to more efficient seed dispersal, increasing the genetic connectivity over long distances.

Genetic structure of a widespread alpine shrub Rhododendron aureum (Ericaceae) across East Asia

The vast territory of East Asia, including southwestern Beringia, is considered to have been almost ice free during the Pleistocene. Cold-resistant flora may have persisted in this region expanding or contracting its range during the climate cooling. Only a few plant genera have been studied with a sampling area across their entire geographic range in East Asia; therefore, the understanding of the biogeographic history of alpine flora in this region remains limited. In the present study, genetic variation and population structure in 21 populations of the alpine shrub Rhododendron aureum across its range in East Asia were assessed using 18 microsatellite loci. Phylogenetic analyses revealed three main genetic groups: Siberia, Northeast, and North Pacific. According to the geographical pattern of genetic diversity, the North Pacific group includes populations from Kamchatka, south of Russian Far East, and territories close to central Japan. This group is the most diverse and likely diverged earlier than the Siberia and Northeast groups. Ecological niche modeling predicts range expansion of this species during the period of cooling and, together with demographic history, suggests that the divergence between the three main genetic groups predated the Last Glacial Maximum. Similar to other cold-resistant species such as Larix sibirica and Juniperus communis, the pattern of genetic diversity of R. aureum supports the survival of the species at high latitudes during the Pleistocene with limited contribution of the southern populations to expansion of the species range to the Northeast region and Siberia.

The Role of Hybridisation in the Making of the Species-Rich Arctic-Alpine Genus Saxifraga (Saxifragaceae)

Evolutionary processes fuelling rapid species diversification are not yet fully understood, although their major contribution to overall patterns of plant biodiversity is well established. Hybridisation is among the least understood of these processes, despite its multifaceted role in speciation processes being widely accepted. Species of the large arctic-alpine genus Saxifraga are notorious for their ability to hybridise; however, the overall role of hybridisation and polyploidisation for the diversification of this genus remains unknown. Here, we provide a comprehensive genus-wide review of hybridisation accounts and ploidy levels. We find that the sections of Saxifraga vary greatly in their propensity to hybridise. The majority of natural hybridisation accounts are from recent localised events (n = 71). Hybridisation hotspots were located in the Pyrenees and the European Alps, thus contrasting with the overall distribution of species richness in the genus. Hybrids or hybrid populations are often short-lived in Saxifraga due to a multitude of reproductive barriers, most commonly low F1 hybrid fertility. However, these barriers are not always fully effective, allowing for backcrossing and the formation of hybrid swarms. In addition, we find that the incidence of polyploidy varies widely across different sections of Saxifraga, with species-rich sections Porphyrion and Saxifraga showing divergent polyploidy proportions. Overall, we show that hybridisation and polyploidisation played differential roles in the diversification of this large genus. Nevertheless, a significant proportion of species are yet to be scrutinised, particularly among the Asian Saxifraga species, illustrating the need for systematic further study to fully unravel the role of hybridisation during the evolution of Saxifraga.

Landscape and Climate Influence the Patterns of Genetic Diversity and Inbreeding in Cerrado Plant Species

The anthropization of the landscape of the Cerrado biome that has occurred over the past few decades has fragmented its natural environments, impacting the connectivity of the plant populations and altering their gene flow. Plant species may also reduce population size in response to sub-optimal climatic and environmental conditions, and observed distribution patterns may align with theoretical schemes, such as the center–periphery model, that is, it is possible that populations on the edge have lower genetic diversity than center populations, theoretically submitted to environmental conditions closer to the optimum. In this context, we evaluate whether the genetic diversity and inbreeding coefficients of Cerrado plant species are affected by landscape features and climate characteristics, and in particular, if the distribution of the genetic diversity of these plants is consistent with the center–periphery model. To do this, we conducted a literature search for genetic studies of Cerrado plant populations using Scopus, Web of Science, and Scielo databases and the species found were used as a proxy to explore patterns throughout the biome. The data were analyzed using generalized linear mixed models (GLMM) and multiple matrix regressions (MMRRs) to evaluate the effects of landscape features and climatic variables on the observed (HO) and expected heterozygosity (HE), allelic richness (AR) and inbreeding (Fis) patterns of the local populations. The landscape was evaluated in terms of the percentage land cover of agriculture (AG), forestry (FO), remnant vegetation (RV), urban areas (UA), pasture (PA), and water (WA) within buffers of 1 km, 3 km, and 5 km around the study populations. We analyzed 121 populations of 31 plant species. The GLMMs showed that HO was affected by FO regardless of buffer size, while HE was also affected by FO, but also by WA and UA. AR was affected by WA and UA in all three buffer zones while the Fis was affected by FO and AU. The MMRRs showed that WA may affect HO, HE, and Fis within the 1 km buffer, while FO affects HO and UA affects AR within the 5 km buffer. In the case of the 1 km and 3 km buffers, however, the geographic distance between populations was identified as a factor determining the genetic diversity and inbreeding indices, indicating that isolation by distance may be an important factor defining the breeding patterns of the Cerrado plant populations. The GLMMs and MMRRs also showed that the mean annual temperature (MAT) and, to a lesser extent, isothermality (ISO) can explain the variation in genetic diversity observed in the Cerrado plant populations. We also found that the center–periphery model fits the distribution pattern observed in most of the species evaluated, including Annona crassiflora,Annona coriacea, Copaifera langsdorffii, and Eugenia dysenterica. Our results indicate that changes in the climate and the landscape of Brazilian Cerrado must be considered carefully to guarantee minimizing the impacts of these processes on the genetic diversity of Cerrado plant species and ensuring the long-term conservation of these species in this biome.

Climate Change and Alpine Screes: No Future for Glacial Relict Papaver occidentale (Papaveraceae) in Western Prealps

Glacial relicts, especially those with very narrow habitat requirements, are particularly affected by global warming. We considered Papaver occidentale, a glacial relict endemic to the Western Prealps, belonging to the alpine poppy complex (P. alpinum aggr.), as a model taxon to study the actual status and potential future distribution of species restricted to particular microrefugia. For this study, all known localities were visited, each population was georeferenced and the number of individuals was estimated. Species Distribution Modelling (SDM) was used to evaluate the present and future potential distribution range and habitat suitability, taking into account the specificity of its habitat (calcareous screes). According to our study, there are globally 19 natural populations of P. occidentale, and a total of about 30,000 individuals. The taxon is a highly specialized alpine plant growing in the majority of natural sites between 1900 and 2100 m a.s.l. on north-facing screes. Predictions for the end of the 21st century indicate that a suitable area will significantly decrease (0–30% remaining). Under the most severe climatic scenarios (RCP 8.5), the species risks complete extinction. The long-term in situ conservation of P. occidentale, and all other taxa of the P. alpinum complex, is unlikely to be achieved without slowing global climate change. More generally, our fine-scale study shows that local environmental buffering of large-scale climate change in high-mountain flora may be very limited in specialised taxa of patchy environments such as screes.

Host use diversification during range shifts shapes global variation in Lepidopteran dietary breadth

Niche breadths tend to be greater at higher latitudes. This pattern is frequently assumed to emerge from the cumulative effects of multiple, independent local adaptation events along latitudinal environmental gradients, although evidence that generalization is more beneficial at higher-latitude locations remains equivocal. Here I propose an alternative hypothesis: that latitudinal variation in niche breadths emerges as a non-adaptive consequence of range shift dynamics. Based on analysis of a global dataset comprising more than 6,934 globally distributed dietary records from 4,410 Lepidopteran species, this hypothesis receives robust support. Population-level dietary niche breadths are better explained by the relative position of the population within its geographic range and the species' poleward range extent than by the latitude of diet observation. Broader diets are observed closer to poleward range limits and in species that have attained higher latitudes. Moreover, latitudinal variation in diet breadth is more prominent within and among species undergoing rapid, contemporary range shifts than for species with more stable ranges. Together these results suggest that latitudinal patterns in niche breadth represent a transient and emergent property of recent geographic range dynamics and need not require underlying gradients in selective agents or fitness trade-offs. The results have wide-ranging implications for global ecology and for anticipating changes in host use during ongoing distributional shifts of pests and disease vectors.

Persistence of arctic-alpine flora during 24,000 years of environmental change in the Polar Urals

Plants adapted to extreme conditions can be at high risk from climate change; arctic-alpine plants, in particular, could "run out of space" as they are out-competed by expansion of woody vegetation. Mountain regions could potentially provide safe sites for arctic-alpine plants in a warmer climate, but empirical evidence is fragmentary. Here we present a 24,000-year record of species persistence based on sedimentary ancient DNA (sedaDNA) from Lake Bolshoye Shchuchye (Polar Urals). We provide robust evidence of long-term persistence of arctic-alpine plants through large-magnitude climate changes but document a decline in their diversity during a past expansion of woody vegetation. Nevertheless, most of the plants that were present during the last glacial interval, including all of the arctic-alpines, are still found in the region today. This underlines the conservation significance of mountain landscapes via their provision of a range of habitats that confer resilience to climate change, particularly for arctic-alpine taxa.

Can we predict which species win when new habitat becomes available?

Land cover change is a key component of anthropogenic global environmental change, contributing to changes in environmental conditions of habitats. Deforestation is globally the most widespread and anthropogenically driven land cover change leading to conversion from closed forest to open non-forest habitat. This study investigates the relative roles of geographic features, characteristics of species climatic niche and species traits in determining the ability of open-habitat plant species to take advantage of recently opened habitats. We use current occurrence records of 18 herbaceous, predominantly open-habitat species of the genus Acaena (Rosaceae) to determine their prevalence in recently opened habitat. We tested correlation of species prevalence in anthropogenically opened habitat with (i) geographic features of the spatial distribution of open habitat, (ii) characteristics of species climatic niche, and (iii) species traits related to dispersal. While primary open habitat (naturally open) was characterised by cold climates, secondary open habitat (naturally closed but anthropogenically opened) is characterised by warmer and wetter conditions. We found high levels of variation in the species prevalence in secondary open habitat indicating species differences in their ability to colonise newly opened habitat. For the species investigated, geographical features of habitat and climatic niche factors showed generally stronger relationships with species prevalence in secondary open habitat than functional traits. Therefore, for small herbaceous species, geographical features of habitat and environmental factors appear to be more important than species functional traits for facilitating expansion into secondary open habitats. Our results suggested that the land cover change might have triggered the shifts of factors controlling open-habitat plant distributions from the competition with forest trees to current environmental constraints.

Relationships between Tertiary relict and circumboreal woodland floras: a case study in Chimaphila (Ericaceae)

BACKGROUND AND AIMS

Tertiary relict and Arctic/circumboreal distributions are two major patterns of Northern Hemisphere intercontinental disjunctions with very different histories. Each has been well researched, but members of one biome have generally not been incorporated in the biogeographical analyses of the other, and links or transitions between these two biomes have rarely been addressed.

METHODS

Phylogenies of Chimaphila were generated based on cpDNA and nuclear ITS, using Bayesian and maximum likelihood methods. A time-calibrated phylogeny was generated using BEAST. Ancestral area reconstruction was inferred using both statistical dispersal-vicariance analysis and a dispersal-extinction-cladogenesis model.

KEY RESULTS

The Chimaphila crown group was estimated to have originated in the early Miocene. The lineages of C. umbellata diverged early, but its present circumboreal distribution was not achieved until around the middle Pliocene or later. Sister to this is a clade of four species with Tertiary relict distribution. Among these, two expansions occurred from North America to Asia, probably via the Bering Land Bridge, generating its current disjunctions.

CONCLUSIONS

Our data concur with a few other studies, indicating that the circumboreal woodland biome has an older origin than most true Arctic-alpine taxa, having gradually recruited taxa since the early Oligocene. For the origin of Asia-North America disjunctions in Chimaphila, an 'out-of-America' migration was supported. It is not clear in which direction Pyroloideae lineages moved between Tertiary relict disjunctions and Arctic/circumboreal distributions; each biome might have recruited species from the other.

Contrasting endemism in pond-dwelling cyclic parthenogens: the Daphnia curvirostris species group (Crustacea: Cladocera)

Pond-dwelling cyclic parthenogens are often proposed to be highly vagile. However, the Holarctic biogeography of parthenogens has been hampered by very limited sampling in the eastern Palearctic. Here we examine the geographic boundaries, diversity, and connectivity across the Palearctic for the Daphnia curvirostris complex (Cladocera: Daphniidae). Nuclear (HSP90) and mitochondrial (ND2) sequence data supported the existence of five main clades (most of which corresponded to presumptive species) with one eastern Palearctic clade being novel to this study (the average mitochondrial genetic divergence from known species was 19.2%). D. curvirostris s.s. was geographically widespread in the Palearctic, with a population genetic signature consistent with postglacial expansion. The Eastern Palearctic had local nine endemic species and/or subclades (other Holarctic regions lacked more than one endemic subclade). Even though several endemic species appeared to have survived Pleistocene glaciation in the eastern Palearctic, much of the Palearctic has been recolonized by D. curvirostris s.str. from a Western Palearctic refugium. A disjunct population in Mexico also shared its haplotypes with D. curvirostris s.str., consistent with a recent introduction. The only apparently endemic North American lineage was detected in a thermally disturbed pond system in northwestern Alaska. Our results for pond-dwelling cyclic parthenogens further support the hypothesis that the Eastern Palearctic is a diversity hotspot for freshwater invertebrates.

Effects of sea ice on Arctic biota: an emerging crisis discipline

The rapid decline in Arctic sea ice (ASI) extent, area and volume during recent decades is occurring before we can understand many of the mechanisms through which ASI interacts with biological processes both at sea and on land. As a consequence, our ability to predict and manage the effects of this enormous environmental change is limited, making this a crisis discipline Here, we propose a framework to study these effects, defining direct effects as those acting on life-history events of Arctic biota, and indirect effects, where ASI acts upon biological systems through chains of events, normally involving other components of the physical system and/or biotic interactions. Given the breadth and complexity of ASI's effects on Arctic biota, Arctic research requires a truly multidisciplinary approach to address this issue. In the absence of effective global efforts to tackle anthropogenic global warming, ASI will likely continue to decrease, compromising the conservation of many ASI-related taxonomic groups and ecosystems. Mitigation actions will rely heavily on the knowledge acquired on the mechanisms and components involved with the biological effects of ASI.

No borders during the post-glacial assembly of European bryophytes

Climatic fluctuations during the Last Glacial Maximum (LGM) exerted a profound influence on biodiversity patterns, but their impact on bryophytes, the second most diverse group of land plants, has been poorly documented. Approximate Bayesian computations based on coalescent simulations showed that the post-glacial assembly of European bryophytes involves a complex history from multiple sources. The contribution of allochthonous migrants was 95-100% of expanding populations in about half of the 15 investigated species, which is consistent with the globally balanced genetic diversities and extremely low divergence observed among biogeographical regions. Such a substantial contribution of allochthonous migrants in the post-glacial assembly of Europe is unparalleled in other plants and animals. The limited role of northern micro-refugia, which was unexpected based on bryophyte life-history traits, and of southern refugia, is consistent with recent palaeontological evidence that LGM climates in Eurasia were much colder and drier than what palaeoclimatic models predict.

Molecular Phylogeography and Ecological Niche Modeling of Sibbaldia procumbens s.l. (Rosaceae)

The phylogeographical analysis and ecological niche modeling (ENM) of the widely distributed Northern Hemisphere Sibbaldia procumbens s.l. can help evaluate how tectonic motion and climate change helped shape the current distribution patterns of this species. Three chloroplast regions (the atpI-atpH and trnL-trnF intergenic spacers and the trnL intron) were obtained from 332 (156 from present study and 176 from the previous study) individuals of S. procumbens s.l. An unrooted haplotype network was constructed using the software NETWORK, while BEAST was used to estimate the divergence times among haplotypes. ENM was performed by MAXENT to explore the historical dynamic distribution of S. procumbens s.l. The haplotype distribution demonstrates significant phylogeographical structure (N_ST > G_ST; P < 0.01). The best partitioning of genetic diversity by SAMOVA produced three groups, while the time to the most recent common ancestor of all haplotypes was estimated to originate during the Miocene, with most of the haplotype diversity having occurred during the Quaternary. The MAXENT analysis showed S. procumbens s.l. had a wider distribution range during the last glacial maximum and a narrower distribution range during the last interglacial, with predictions into the future showing the distribution range of S. procumbens s.l. shrinking.

Postglacial colonization history reflects in the genetic structure of natural populations of Festuca rubra in Europe

We conducted a large-scale population genetic survey of genetic diversity of the host grass Festuca rubra s.l., which fitness can be highly dependent on its symbiotic fungus Epichloë festucae, to evaluate genetic variation and population structure across the European range. The 27 studied populations have previously been found to differ in frequencies of occurrence of the symbiotic fungus E. festucae and ploidy levels. As predicted, we found decreased genetic diversity in previously glaciated areas in comparison with nonglaciated regions and discovered three major maternal genetic groups: southern, northeastern, and northwestern Europe. Interestingly, host populations from Greenland were genetically similar to those from the Faroe Islands and Iceland, suggesting gene flow also between those areas. The level of variation among populations within regions is evidently highly dependent on the postglacial colonization history, in particular on the number of independent long-distance seed colonization events. Yet, also anthropogenic effects may have affected the population structure in F. rubra. We did not observe higher fungal infection rates in grass populations with lower levels of genetic variability. In fact, the fungal infection rates of E. festucae in relation to genetic variability of the host populations varied widely among geographical areas, which indicate differences in population histories due to colonization events and possible costs of systemic fungi in harsh environmental conditions. We found that the plants of different ploidy levels are genetically closely related within geographic areas indicating independent formation of polyploids in different maternal lineages.

Flower-visitor communities of an arcto-alpine plant-Global patterns in species richness, phylogenetic diversity and ecological functioning

Pollination is an ecosystem function of global importance. Yet, who visits the flower of specific plants, how the composition of these visitors varies in space and time and how such variation translates into pollination services are hard to establish. The use of DNA barcodes allows us to address ecological patterns involving thousands of taxa that are difficult to identify. To clarify the regional variation in the visitor community of a widespread flower resource, we compared the composition of the arthropod community visiting species in the genus Dryas (mountain avens, family Rosaceae), throughout Arctic and high-alpine areas. At each of 15 sites, we sampled Dryas visitors with 100 sticky flower mimics and identified specimens to Barcode Index Numbers (BINs) using a partial sequence of the mitochondrial COI gene. As a measure of ecosystem functioning, we quantified variation in the seed set of Dryas. To test for an association between phylogenetic and functional diversity, we characterized the structure of local visitor communities with both taxonomic and phylogenetic descriptors. In total, we detected 1,360 different BINs, dominated by Diptera and Hymenoptera. The richness of visitors at each site appeared to be driven by local temperature and precipitation. Phylogeographic structure seemed reflective of geological history and mirrored trans-Arctic patterns detected in plants. Seed set success varied widely among sites, with little variation attributable to pollinator species richness. This pattern suggests idiosyncratic associations, with function dominated by few and potentially different taxa at each site. Taken together, our findings illustrate the role of post-glacial history in the assembly of flower-visitor communities in the Arctic and offer insights for understanding how diversity translates into ecosystem functioning.

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.

The role of sea ice for vascular plant dispersal in the Arctic

Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arctic. To assess its role for postglacial colonization in the North Atlantic region, we compiled data on the first Late Glacial to Holocene occurrence of vascular plant species in East Greenland, Iceland, the Faroe Islands and Svalbard. For each record, we reconstructed likely past dispersal events using data on species distributions and genetics. We compared these data to sea-ice reconstructions to evaluate the potential role of sea ice in these past colonization events and finally evaluated these results using a compilation of driftwood records as an independent source of evidence that sea ice can disperse biological material. Our results show that sea ice was, in general, more prevalent along the most likely dispersal routes at times of assumed first colonization than along other possible routes. Also, driftwood is frequently dispersed in regions that have sea ice today. Thus, sea ice may act as an important dispersal agent. Melting sea ice may hamper future dispersal of Arctic plants and thereby cause more genetic differentiation. It may also limit the northwards expansion of competing boreal species, and hence favour the persistence of Arctic species.

Genome-Wide Analysis of Colonization History and Concomitant Selection in Arabidopsis lyrata

The high climatic variability in the past hundred thousand years has affected the demographic and adaptive processes in many species, especially in boreal and temperate regions undergoing glacial cycles. This has also influenced the patterns of genome-wide nucleotide variation, but the details of these effects are largely unknown. Here we study the patterns of genome-wide variation to infer colonization history and patterns of selection of the perennial herb species Arabidopsis lyrata, in locally adapted populations from different parts of its distribution range (Germany, UK, Norway, Sweden, and USA) representing different environmental conditions. Using site frequency spectra based demographic modeling, we found strong reduction in the effective population size of the species in general within the past 100,000 years, with more pronounced effects in the colonizing populations. We further found that the northwestern European A. lyrata populations (UK and Scandinavian) are more closely related to each other than with the Central European populations, and coalescent based population split modeling suggests that western European and Scandinavian populations became isolated relatively recently after the glacial retreat. We also highlighted loci showing evidence for local selection associated with the Scandinavian colonization. The results presented here give new insights into postglacial Scandinavian colonization history and its genome-wide effects.

Late Pleistocene origin of the entire circumarctic range of the arctic-alpine plant Kalmia procumbens

The circumarctic ranges of arctic-alpine plants are thought to have been established in the late Pliocene/early Pleistocene, when the modern arctic tundra was formed in response to climate cooling. Previous findings of range-wide genetic structure in arctic-alpine plants have been thought to support this hypothesis, but few studies have explicitly addressed the temporal framework of the genetic structure. Here, we estimated the demographic history of the genetic structure in the circumarctic Kalmia procumbens using sequences of multiple nuclear loci and examined whether its genetic structure reflects prolonged isolation throughout the Pleistocene. Both Bayesian clustering and phylogenetic analyses revealed genetic distinction between alpine and arctic regions, whereas detailed groupings were somewhat discordant between the analyses. By assuming a population grouping based on the phylogenetic analyses, which likely reflects a deeper intraspecific divergence, we conducted model-based analyses and demonstrated that the intraspecific genetic divergence in K. procumbens likely originated during the last glacial period. Thus, there is no need to postulate range separation throughout the Pleistocene to explain the current genetic structure in this species. This study demonstrates that range-wide genetic structure in arctic-alpine plants does not necessarily result from the late Pliocene/early Pleistocene origin of their circumarctic ranges and emphasizes the importance of a temporal framework of the current genetic structure for understanding the biogeographic history of the arctic flora.

Population genetic analysis of a global collection of Fragaria vesca using microsatellite markers

The woodland strawberry, Fragaria vesca, holds great promise as a model organism. It not only represents the important Rosaceae family that includes economically important species such as apples, pears, peaches and roses, but it also complements the well-known model organism Arabidopsis thaliana in key areas such as perennial life cycle and the development of fleshy fruit. Analysis of wild populations of A. thaliana has shed light on several important developmental pathways controlling, for example, flowering time and plant growth, suggesting that a similar approach using F. vesca might add to our understanding on the development of rosaceous species and perennials in general. As a first step, 298 F. vesca plants were analyzed using microsatellite markers with the primary aim of analyzing population structure and distribution of genetic diversity. Of the 68 markers tested, 56 were polymorphic, with an average of 4.46 alleles per locus. Our analysis partly confirms previous classification of F. vesca subspecies in North America and suggests two groups within the subsp. bracteata. In addition, F. vesca subsp. vesca forms a single global population with evidence that the Icelandic group is a separate cluster from the main Eurasian population.

Vascular plant biodiversity of the lower Coppermine River valley and vicinity (Nunavut, Canada): an annotated checklist of an Arctic flora

The Coppermine River in western Nunavut is one of Canada's great Arctic rivers, yet its vascular plant flora is poorly known. Here, we report the results of a floristic inventory of the lower Coppermine River valley and vicinity, including Kugluk (Bloody Falls) Territorial Park and the hamlet of Kugluktuk. The study area is approximately 1,200 km2, extending from the forest-tundra south of the treeline to the Arctic coast. Vascular plant floristic data are based on a review of all previous collections from the area and more than 1,200 new collections made in 2014. Results are presented in an annotated checklist, including citation of all specimens examined, comments on taxonomy and distribution, and photographs for a subset of taxa. The vascular plant flora comprises 300 species (311 taxa), a 36.6% increase from the 190 species documented by previous collections made in the area over the last century, and is considerably more diverse than other local floras on mainland Nunavut. We document 207 taxa for Kugluk (Bloody Falls) Territorial Park, an important protected area for plants on mainland Nunavut. A total of 190 taxa are newly recorded for the study area. Of these, 14 taxa (13 species and one additional variety) are newly recorded for Nunavut (Allium schoenoprasum, Carex capitata, Draba lonchocarpa, Eremogone capillaris subsp. capillaris, Sabulina elegans, Eleocharis quinqueflora, Epilobium cf. anagallidifolium, Botrychium neolunaria, Botrychium tunux, Festuca altaica, Polygonum aviculare, Salix ovalifolia var. arctolitoralis, Salix ovalifolia var. ovalifolia and Stuckenia pectinata), seven species are newly recorded for mainland Nunavut (Carex gynocrates, Carex livida, Cryptogramma stelleri, Draba simmonsii, Festuca viviparoidea subsp. viviparoidea, Juncus alpinoarticulatus subsp. americanus and Salix pseudomyrsinites) and 56 range extensions are reported. The psbA-trnH and rbcL DNA sequence data were used to help identify the three Botrychium taxa recorded in the study area. Three new combinations are proposed: Petasites frigidus subsp. sagittatus (Banks ex Pursh) Saarela, Carex petricosa subsp. misandroides (Fernald) Saarela and Carex simpliciuscula subsp. subholarctica (T. V. Egorova) Saarela.

Glacial refugia and postglacial expansion of the alpine-prealpine plant species Polygala chamaebuxus

The shrubby milkwort (Polygala chamaebuxus L.) is widely distributed in the Alps, but occurs also in the lower mountain ranges of Central Europe such as the Franconian Jura or the Bohemian uplands. Populations in these regions may either originate from glacial survival or from postglacial recolonization. In this study, we analyzed 30 populations of P. chamaebuxus from the whole distribution range using AFLP (Amplified Fragment Length Polymorphism) analysis to identify glacial refugia and to illuminate the origin of P. chamaebuxus in the lower mountain ranges of Central Europe. Genetic variation and the number of rare fragments within populations were highest in populations from the central part of the distribution range, especially in the Southern Alps (from the Tessin Alps and the Prealps of Lugano to the Triglav Massiv) and in the middle part of the northern Alps. These regions may have served, in accordance with previous studies, as long-term refugia for the glacial survival of the species. The geographic pattern of genetic variation, as revealed by analysis of molecular variance, Bayesian cluster analysis and a PopGraph genetic network was, however, only weak. Instead of postglacial recolonization from only few long-term refugia, which would have resulted in deeper genetic splits within the data set, broad waves of postglacial expansion from several short-term isolated populations in the center to the actual periphery of the distribution range seem to be the scenario explaining the observed pattern of genetic variation most likely. The populations from the lower mountain ranges in Central Europe were more closely related to the populations from the southwestern and northern than from the nearby eastern Alps. Although glacial survival in the Bohemian uplands cannot fully be excluded, P. chamaebuxus seems to have immigrated postglacially from the southwestern or central-northern parts of the Alps into these regions during the expansion of the pine forests in the early Holocene.

High migration rates shape the postglacial history of amphi-Atlantic bryophytes

Paleontological evidence and current patterns of angiosperm species richness suggest that European biota experienced more severe bottlenecks than North American ones during the last glacial maximum. How well this pattern fits other plant species is less clear. Bryophytes offer a unique opportunity to contrast the impact of the last glacial maximum in North America and Europe because about 60% of the European bryoflora is shared with North America. Here, we use population genetic analyses based on approximate Bayesian computation on eight amphi-Atlantic species to test the hypothesis that North American populations were less impacted by the last glacial maximum, exhibiting higher levels of genetic diversity than European ones and ultimately serving as a refugium for the postglacial recolonization of Europe. In contrast with this hypothesis, the best-fit demographic model involved similar patterns of population size contractions, comparable levels of genetic diversity and balanced migration rates between European and North American populations. Our results thus suggest that bryophytes have experienced comparable demographic glacial histories on both sides of the Atlantic. Although a weak, but significant genetic structure was systematically recovered between European and North American populations, evidence for migration from and towards both continents suggests that amphi-Atlantic bryophyte population may function as a metapopulation network. Reconstructing the biogeographic history of either North American or European bryophyte populations therefore requires a large, trans-Atlantic geographic framework.