Population genomic evidence for plant glacial survival in Scandinavia

Quaternary glaciations have played a major role in shaping the genetic diversity and distribution of plant species. Strong palaeoecological and genetic evidence supports a postglacial recolonization of most plant species to northern Europe from southern, eastern and even western glacial refugia. Although highly controversial, the existence of small in situ glacial refugia in northern Europe has recently gained molecular support. We used genomic analyses to examine the phylogeography of a species that is critical in this debate. Carex scirpoidea Michx subsp. scirpoidea is a dioecious, amphi‐Atlantic arctic–alpine sedge that is widely distributed in North America, but absent from most of Eurasia, apart from three extremely disjunct populations in Norway, all well within the limits of the Weichselian ice sheet. Range‐wide population sampling and variation at 5,307 single nucleotide polymorphisms show that the three Norwegian populations comprise unique evolutionary lineages divergent from Greenland with high between‐population divergence. The Norwegian populations have low within‐population genetic diversity consistent with having experienced genetic bottlenecks in glacial refugia, and host private alleles that probably accumulated in long‐term isolated populations. Demographic analyses support a single, pre‐Weichselian colonization into Norway from East Greenland, and subsequent divergence of the three populations in separate refugia. Other refugial areas are identified in North‐east Greenland, Minnesota/Michigan, Colorado and Alaska. Admixed populations in British Columbia and West Greenland indicate postglacial contact. Taken together, evidence from this study strongly indicates in situ glacial survival in Scandinavia.     

The east‐west‐north colonization history of the Mediterranean and Europe by the coastal plant Carex extensa (Cyperaceae)

Coastal plants are ideal models for studying the colonization routes of species because of the simple linear distributions of these species. Carex extensa occurs mainly in salt marshes along the Mediterranean and European coasts. Variation in cpDNA sequences, amplified fragment length polymorphisms (AFLPs) and simple sequence repeats (SSRs) of 24 populations were analysed to reconstruct its colonization history. Phylogenetic relationships indicate that C. extensa together with the South American Carex vixdentata and the southern African Carex ecklonii form a monophyletic group of halophilic species. Analyses of divergence times suggest that early lineage diversification may have occurred between the late Miocene and the late Pliocene (Messinian crisis). Phylogenetic and network analyses of cpDNA variation revealed the monophyly of the species and an ancestral haplotype contained in populations of the eastern Mediterranean. The AFLP and SSR analyses support a pattern of variation compatible with these two lineages. These analyses also show higher levels of genetic diversity and differentiation in the eastern population group, which underwent an east‐to‐west Mediterranean colonization. Quaternary climatic oscillations appear to have been responsible for the split between these two lineages. Secondary contacts may have taken place in areas near the Ligurian Sea in agreement with the gene flow detected in Corsican populations. The AFLP and SSR data accord with the ‘tabula rasa’ hypothesis in which a recent and rapid colonization of northern Europe took place from the western Mediterranean after the Last Glacial Maximum. The unbalanced west‐east vs. west‐north colonization may be as a result of ‘high density blocking’ effect.     

A dynamic history of admixture from Mediterranean and Carpathian glacial refugia drives genomic diversity in the bank vole

Understanding the historical contributions of differing glacial refugia is key to evaluating the roles of microevolutionary forces, such as isolation, introgression, and selection in shaping genomic diversity in present‐day populations. In Europe, where both Mediterranean and extra‐Mediterranean (e.g., Carpathian) refugia of the bank vole (Clethrionomys glareolus) have been identified, mtDNA indicates that extra‐Mediterranean refugia were the main source of colonization across the species range, while Mediterranean peninsulas harbor isolated, endemic lineages. Here, we critically evaluate this hypothesis using previously generated genomic data (>6,000 SNPs) for over 800 voles, focusing on genomic contributions to bank voles in central Europe, a key geographic area in considering range‐wide colonization. The results provide clear evidence that both extra‐Mediterranean (Carpathian) and Mediterranean (Spanish, Calabrian, and Balkan) refugia contributed to the ancestry and genomic diversity of bank vole populations across Europe. Few strong barriers to dispersal and frequent admixture events in central Europe have led to a prominent mid‐latitude peak in genomic diversity. Although the genomic contribution of the centrally located Carpathian refugium predominates, populations in different parts of Europe have admixed origins from Mediterranean (28%–47%) and the Carpathian (53%–72%) sources. We suggest that the admixture from Mediterranean refugia may have provisioned adaptive southern alleles to more northern populations, facilitating the end‐glacial spread of the admixed populations and contributing to increased bank vole diversity in central Europe. This study adds critical details to the complex end‐glacial colonization history of this well‐studied organism and underscores the importance of genomic data in phylogeographic interpretation.     

Identifying refugia from climate change using coupled ecological and genetic data in a transitional Mediterranean‐temperate tree species

Populations occurring in areas of overlap between the current and future distribution of a species are particularly important because they can represent “refugia from climate change”. We coupled ecological and range‐wide genetic variation data to detect such areas and to evaluate the impacts of habitat suitability changes on the genetic diversity of the transitional Mediterranean‐temperate tree Fraxinus angustifolia. We sampled and genotyped 38 natural populations comprising 1006 individuals from across Europe. We found the highest genetic diversity in western and northern Mediterranean populations, as well as a significant west to east decline in genetic diversity. Areas of potential refugia that correspond to approximately 70% of the suitable habitat may support the persistence of more than 90% of the total number of alleles in the future. Moreover, based on correlations between Bayesian genetic assignment and climate, climate change may favour the westward spread of the Black Sea gene pool in the long term. Overall, our results suggest that the northerly core areas of the current distribution contain the most important part of the genetic variation for this species and may serve as in situ macrorefugia from ongoing climate change. However, rear‐edge populations of the southern Mediterranean may be exposed to a potential loss of unique genetic diversity owing to habitat suitability changes unless populations can persist in microrefugia that have facilitated such persistence in the past.     

Molecular markers provide evidence for a broad‐fronted recolonisation of the widespread calcareous grassland species Sanguisorba minor from southern and cryptic northern refugia

• Calcareous grasslands belong to the most species‐rich and endangered habitats in Europe. However, little is known about the origin of the species typically occurring in these grasslands. In this study we analysed the glacial and post‐glacial history of Sanguisorba minor, a typical plant species frequently occurring in calcareous grasslands.
• The study comprised 38 populations throughout the whole distribution range of the species across Europe. We used molecular markers (AFLP) and applied Bayesian cluster analysis as well as spatial principal components analysis (sPCA) to identify glacial refugia and post‐glacial migration routes to Central Europe.
• Our study revealed significant differences in the level of genetic variation and the occurrence of rare fragments within populations of S. minor and a distinct separation of eastern and western lineages. The analyses uncovered traditional southern but also cryptic northern refugia and point towards a broad fronted post‐glacial recolonisation.
• Based on these results we postulate that incomplete lineage sorting may have contributed to the detected pattern of genetic variation and that S. minor recolonised Central Europe post‐glacially from Iberia and northern glacial refugia in France, Belgium or Germany. Our results highlight the importance of refugial areas for the conservation of intraspecific variation in calcareous grassland species.

     

Postglacial recolonization in a cold climate specialist in western Europe: patterns of genetic diversity in the adder (Vipera berus) support the central–marginal hypothesis

Understanding the impact of postglacial recolonization on genetic diversity is essential in explaining current patterns of genetic variation. The central–marginal hypothesis (CMH) predicts a reduction in genetic diversity from the core of the distribution to peripheral populations, as well as reduced connectivity between peripheral populations. While the CMH has received considerable empirical support, its broad applicability is still debated and alternative hypotheses predict different spatial patterns of genetic diversity. Using microsatellite markers, we analysed the genetic diversity of the adder (Vipera berus) in western Europe to reconstruct postglacial recolonization. Approximate Bayesian Computation (ABC) analyses suggested a postglacial recolonization from two routes: a western route from the Atlantic Coast up to Belgium and a central route from the Massif Central to the Alps. This cold‐adapted species likely used two isolated glacial refugia in southern France, in permafrost‐free areas during the last glacial maximum. Adder populations further from putative glacial refugia had lower genetic diversity and reduced connectivity; therefore, our results support the predictions of the CMH. Our study also illustrates the utility of highly variable nuclear markers, such as microsatellites, and ABC to test competing recolonization hypotheses.     

Phylogeography reveals latitudinal population structure in the common herb Plantago coronopus

The increase in gene diversity from high to low latitudes is a widely recognized biogeographical pattern, often shaped by differential effects of Late Quaternary climatic changes. Here, we evaluate the effects of Pleistocene climatic changes from northern Europe to North Africa and their implications on the population differentiation of the widespread, short‐lived herb Plantago coronopus. We used amplified fragment length polymorphism to investigate the population structure and phylogeography of P. coronopus in 273 individuals from 29 populations covering its complete latitudinal range. Although Bayesian clustering, principal coordinates analysis and a consensus UPGMA tree were not fully congruent, two well‐supported clades, associated with distinct latitudinal zones (northern Europe and the Mediterranean region), were revealed as a general pattern. Moreover, populations from the western Atlantic edge and, to a lesser extent, the central Mediterranean region exhibited signs of admixture, suggesting secondary contacts. The admixed populations in the western Atlantic and central Mediterranean are geographically intermediate between the northern and southern lineages. The northernmost lineage exhibited low genetic diversity, a clear sign of a recent colonization. In contrast, populations from the southernmost part of the range showed the highest level of genetic diversity, indicating possible refugia for the species during the Quaternary ice ages. Overall, our study allows spatial structure of the genetic variation of a widespread herb across its latitudinal range to be disentangled and provides insights into how past climatic history influences present genetic patterns. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 618–634.     

Central Asian origin of and strong genetic differentiation among populations of the rare and disjunct Carex atrofusca (Cyperaceae) in the Alps

Aim Carex atrofusca has an arctic–alpine distribution in the Northern Hemisphere, with only a few, disjunct localities known in the European Alps. These alpine populations are declining in number and size. In contrast, C. atrofusca has a wide circumpolar distribution range and is abundant in large parts of the Arctic. The degree of genetic differentiation of the alpine populations and their importance for the conservation of the intraspecific genetic variation of the species is unknown. Location Eurasia and Greenland, with emphasis on the European Alps. Methods We applied amplified fragment length polymorphism (AFLP) fingerprinting and sequences of chloroplast DNA to determine the position of the alpine populations in a circumpolar phylogeography of C. atrofusca and to unravel the patterns of genetic diversity and differentiation within the Alps. Results Two distinct major groups were detected in a neighbour‐joining analysis of AFLP data and in parsimony analysis of chloroplast DNA sequences: one consisting of the populations from Siberia and Greenland and one consisting of all European populations as sister to the populations from Central Asia. Within Europe, the populations from the Tatra Mountains and those from Scotland and Scandinavia formed two well‐supported groups, whereas the alpine populations did not constitute a group of their own. The genetic variation in the Alps was almost completely partitioned among the populations, and the populations were almost invariable. Main conclusions The alpine populations possibly originated due to immigration from Central Asia. The strong differentiation among them suggests that genetic drift has been strongly acting on the populations, either as a consequence of founder events during colonization or due to subsequent reduction of population sizes during warm stages of the Holocene.     

The molecular population structure of the tall forb Cicerbita alpina (Asteraceae) supports the idea of cryptic glacial refugia in central Europe

There is an ongoing debate about the glacial history of non‐arctic species in central and northern Europe. The two main hypotheses are: (1) postglacial colonization from refugia outside this region; (2) glacial survival in microclimatically favourable sites within the periglacial areas. In order to clarify the glacial history of a boreo‐montane tall forb, we analysed AFLPs from populations of Cicerbita alpina through most of its range (Scandinavia, the mountains of central Europe, the Alps, the Pyrenees and the Balkan Peninsula). We found a major differentiation between the Pyrenean population and all others, supported by principal coordinate, neighbour joining and STRUCTURE analyses. Furthermore, three populations from the central and north‐eastern Alps were genetically distinct from the bulk of populations from Scandinavia, central Europe, the Alps and the Balkan Peninsula. Most populations, including those from central and northern Europe, had moderate to high levels of genetic diversity (mean Shannon index H_Sh = 0.292, mean percentage of polymorphic loci P = 54.1%, mean Nei's gene diversity H = 0.195). The results indicate separate glacial refugia in the Pyrenean region and the Italian Alps. Furthermore, they provide evidence of glacial persistence in cryptic refugia north of the Alps, from where Scandinavia and most of the Alps are likely to have been colonized following deglaciation. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 142–154.     

A new scenario for the quaternary history of European beech populations: palaeobotanical evidence and genetic consequences

Here, palaeobotanical and genetic data for common beech (Fagus sylvatica) in Europe are used to evaluate the genetic consequences of long-term survival in refuge areas and postglacial spread. Four large datasets are presented, including over 400 fossil-pollen sites, 80 plant-macrofossil sites, and 450 and 600 modern beech populations for chloroplast and nuclear markers, respectively. The largely complementary palaeobotanical and genetic data indicate that: (i) beech survived the last glacial period in multiple refuge areas; (ii) the central European refugia were separated from the Mediterranean refugia; (iii) the Mediterranean refuges did not contribute to the colonization of central and northern Europe; (iv) some populations expanded considerably during the postglacial period, while others experienced only a limited expansion; (v) the mountain chains were not geographical barriers for beech but rather facilitated its diffusion; and (vi) the modern genetic diversity was shaped over multiple glacial-interglacial cycles. This scenario differs from many recent treatments of tree phylogeography in Europe that largely focus on the last ice age and the postglacial period to interpret genetic structure and argue that the southern peninsulas (Iberian, Italian and Balkan) were the main source areas for trees in central and northern Europe.     

Phylogeography and population structure of European sea bass in the north‐east Atlantic

The European sea bass Dicentrarchus labrax represents a historically and commercially valuable species in the north‐east Atlantic, although the demographic history and the patterns of geographical structure of the species in the north‐east Atlantic remain poorly understood. The present study investigates the population genetic structure of sea bass in north‐western European waters, employing different genetic markers [a portion of the mitochondrial (mt)DNA control region and 13 nuclear microsatellites] aiming to unravel demographic history and population connectivity. The results obtained show a previously unrecognized pattern of population divergence at mtDNA, with three strikingly different lineages identified. Extant sea bass populations, including the Mediterranean lineage, derive from an Atlantic ancestor. A much increased number of nuclear microsatellite loci (comparatively to previous studies) still fail to detect biologically meaningful patterns of spatial genetic structuring in the North Atlantic. Past Pleistocene glacial and interglacial events and some degree of female philopatry might be at the basis of the current geographical separation of the Atlantic lineages that has been identified. Signatures of sudden demographic expansions are more evident in the most recent mitochondrial lineages, and their slight, yet significant, geographical segregation leads to the hypothesis that present‐day spawning grounds for European sea bass may still to some extent be linked to their most recent glacial refugia. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 364–377.     

Postglacial colonization of Europe by the barbastelle bat: agreement between molecular data and past predictive modelling

The barbastelle (Barbastella barbastellus) is a rare forest bat with a wide distribution in Europe. Here, we combine results from the analysis of two mtDNA fragments with species distribution modelling to determine glacial refugia and postglacial colonization routes. We also investigated whether niche conservatism occurs in this species. Glacial refugia were identified in the three southern European peninsulas: Iberia, Italy and the Balkans. These latter two refugia played a major role in the postglacial colonization process, with their populations expanding to England and central Europe, respectively. Palaeo‐distribution models predicted that suitable climatic conditions existed in the inferred refugia during the last glacial maximum (LGM). Nevertheless, the overlap between the current and the LGM distributions was almost inexistent in Italy and in the Balkans, meaning that B. barbastellus populations were forced to shift range between glacial and interglacial periods, a process that probably caused some local extinctions. In contrast, Iberian populations showed a ‘refugia within refugium’ pattern, with two unconnected areas containing stable populations (populations that subsisted during both glacial and interglacial phases). Moreover, the match between LGM models and the refugial areas determined by molecular analysis supported the hypothesis of niche conservatism in B. barbastellus. We argue that geographic patterns of genetic structuring, altogether with the modelling results, indicate the existence of four management units for conservation: Morocco, Iberia, Italy and UK, and Balkans and central Europe. In addition, all countries sampled possessed unique gene pools, thus stressing the need for the conservation of local populations.     

Genetic consequences of glacial survival and postglacial colonization in Norway spruce: combined analysis of mitochondrial DNA and fossil pollen

Norway spruce (Picea abies [L.] Karst.) is a broadly distributed European conifer tree whose history has been intensively studied by means of fossil records to infer the location of full‐glacial refugia and the main routes of postglacial colonization. Here we use recently compiled fossil pollen data as a template to examine how past demographic events have influenced the species’ modern genetic diversity. Variation was assessed in the mitochondrial nad1 gene containing two minisatellite regions. Among the 369 populations (4876 trees) assayed, 28 mitochondrial variants were identified. The patterns of population subdivision superimposed on interpolated fossil pollen distributions indicate that survival in separate refugia and postglacial colonization has led to significant structuring of genetic variation in the southern range of the species. The populations in the northern range, on the other hand, showed a shallow genetic structure consistent with the fossil pollen data, suggesting that the vast northern range was colonized from a single refugium. Although the genetic diversity decreased away from the putative refugia, there were large differences between different colonization routes. In the Alps, the diversity decreased over short distances, probably as a result of population bottlenecks caused by the presence of competing tree species. In northern Europe, the diversity was maintained across large areas, corroborating fossil pollen data in suggesting that colonization took place at high population densities. The genetic diversity increased north of the Carpathians, probably as a result of admixture of expanding populations from two separate refugia.     

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 genomic diversity in the bank vole at the northern apex of a range expansion: The role of multiple colonizations and end‐glacial refugia

The history of repeated northern glacial cycling and southern climatic stability has long dominated explanations for how genetic diversity is distributed within temperate species in Eurasia and North America. However, growing evidence indicates the importance of cryptic refugia for northern colonization dynamics. An important geographic region to assess this is Fennoscandia, where recolonization at the end of the last glaciation was restricted to specific routes and temporal windows. We used genomic data to analyse genetic diversity and colonization history of the bank vole (Myodes glareolus) throughout Europe (>800 samples) with Fennoscandia as the northern apex. We inferred that bank voles colonized Fennoscandia multiple times by two different routes; with three separate colonizations via a southern land‐bridge route deriving from a “Carpathian” glacial refugium and one via a north‐eastern route from an “Eastern” glacial refugium near the Ural Mountains. Clustering of genome‐wide SNPs revealed high diversity in Fennoscandia, with eight genomic clusters: three of Carpathian origin and five Eastern. Time estimates revealed that the first of the Carpathian colonizations occurred before the Younger Dryas (YD), meaning that the first colonists survived the YD in Fennoscandia. Results also indicated that introgression between bank and northern red‐backed voles (Myodes rutilus) took place in Fennoscandia just after end‐glacial colonization. Therefore, multiple colonizations from the same and different cryptic refugia, temporal and spatial separations and interspecific introgression have shaped bank vole genetic variability in Fennoscandia. Together, these processes drive high genetic diversity at the apex of the northern expansion in this emerging model species.     

Northern areas as refugia for temperate species under current climate warming: Atlantic salmon (Salmo salar L.) as a model in northern Europe

In this work, patterns of geographical genetic diversity in Atlantic salmon Salmo salar were studied across the whole Atlantic Arc; whether these patterns (and thus genetic population structure) were affected by water temperatures was also evaluated. Salmo salar populations were characterized using microsatellite loci and then analysed with reference to ocean surface temperature data from across the region. Analysis showed the presence of a latitudinal cline of genetic variability (higher in northern areas) and water temperatures (sea surface temperatures) determining genetic population structure (the latter in combination with genetic drift in southern populations). Under the current global change scenario, northern areas of Europe would constitute refugia for diversity in the future. This is effectively the inverse of what appears to have happened in glacial refugia during the last glacial maximum. From this perspective, the still abundant and large northern populations S. salar should be considered as precious as the small almost relict southern ones and given appropriate protection. Careful management of the species, coordinated across countries and latitudes, is needed in order to avoid its extinction in Europe.     

Imprints of multiple glacial refugia in the Pyrenees revealed by phylogeography and palaeodistribution modelling of an endemic spider

Mediterranean mountain ranges harbour highly endemic biota in islandlike habitats. Their topographic diversity offered the opportunity for mountain species to persist in refugial areas during episodes of major climatic change. We investigate the role of Quaternary climatic oscillations in shaping the demographic history and distribution ranges in the spider Harpactocrates ravastellus, endemic to the Pyrenees. Gene trees and multispecies coalescent analyses on mitochondrial and nuclear DNA sequences unveiled two distinct lineages with a hybrid zone around the northwestern area of the Catalan Pyrenees. The lineages were further supported by morphological differences. Climatic niche‐based species distribution models (SDMs) identified two lowland refugia at the western and eastern extremes of the mountain range, which would suggest secondary contact following postglacial expansion of populations from both refugia. Neutrality test and approximate Bayesian computation (ABC) analyses indicated that several local populations underwent severe bottlenecks followed by population expansions, which in combination with the deep population differentiation provided evidence for population survival during glacial periods in microrefugia across the mountain range, in addition to the main Atlantic and Mediterranean (western and eastern) refugia. This study sheds light on the complexities of Quaternary climatic oscillations in building up genetic diversity and local endemicity in the southern Europe mountain ranges.     

Spatial genetic structure in Beta vulgaris subsp. maritima and Beta macrocarpa reveals the effect of contrasting mating system,influence of marine currents,and footprints of postglacial recolonization routes

Understanding the factors that contribute to population genetic divergence across a species' range is a long‐standing goal in evolutionary biology and ecological genetics. We examined the relative importance of historical and ecological features in shaping the present‐day spatial patterns of genetic structure in two related plant species, Beta vulgaris subsp. maritima and Beta macrocarpa. Using nuclear and mitochondrial markers, we surveyed 93 populations from Brittany (France) to Morocco – the southern limit of their species' range distribution. Whereas B. macrocarpa showed a genotypic structure and a high level of genetic differentiation indicative of selfing, the population genetic structure of B. vulgaris subsp. maritima was consistent with an outcrossing mating system. We further showed (1) a strong geographic clustering in coastal B. vulgaris subsp. maritima populations that highlighted the influence of marine currents in shaping different lineages and (2) a peculiar genetic structure of inland B. vulgaris subsp. maritima populations that could indicate the admixture of distinct evolutionary lineages and recent expansions associated with anthropogenic disturbances. Spatial patterns of nuclear diversity and differentiation also supported a stepwise recolonization of Europe from Atlantic‐Mediterranean refugia after the last glacial period, with leading‐edge expansions. However, cytoplasmic diversity was not impacted by postglacial recolonization: stochastic long‐distance seed dispersal mediated by major oceanic currents may mitigate the common patterns of reduced cytoplasmic diversity observed for edge populations. Overall, the patterns we documented here challenge the general view of reduced genetic diversity at the edge of a species' range distribution and provide clues for understanding how life‐history and major geographic features interact to shape the distribution of genetic diversity.     

Investigating past range dynamics for a weed of cultivation,Silene vulgaris

Since the last glacial maximum (LGM), many plant and animal taxa have expanded their ranges by migration from glacial refugia. Weeds of cultivation may have followed this trend or spread globally following the expansion of agriculture or ruderal habitats associated with human‐mediated disturbance. We tested whether the range expansion of the weed Silene vulgaris across Europe fit the classical model of postglacial expansion from southern refugia, or followed known routes of the expansion of human agricultural practices. We used species distribution modeling to predict spatial patterns of postglacial expansion and contrasted these with the patterns of human agricultural expansion. A population genetic analysis using microsatellite loci was then used to test which scenario was better supported by spatial patterns of genetic diversity and structure. Genetic diversity was highest in southern Europe and declined with increasing latitude. Locations of ancestral demes from genetic cluster analysis were consistent with areas of predicted refugia. Species distribution models showed the most suitable habitat in the LGM on the southern coasts of Europe. These results support the typical postglacial northward colonization from southern refugia while refuting the east‐to‐west agricultural spread as the main mode of expansion for S. vulgaris. We know that S. vulgaris has recently colonized many regions (including North America and other continents) through human‐mediated dispersal, but there is no evidence for a direct link between the Neolithic expansion of agriculture and current patterns of genetic diversity of S. vulgaris in Europe. Therefore, the history of range expansion of S. vulgaris likely began with postglacial expansion after the LGM, followed by more recent global dispersal by humans.     

Quaternary range dynamics of ecologically divergent species (Edraianthus serpyllifolius and E. tenuifolius,Campanulaceae) within the Balkan refugium

Aim We investigated Quaternary range dynamics of two closely related but ecologically divergent species (cold‐tolerant Edraianthus serpyllifolius and thermophilic Edraianthus tenuifolius) with overlapping distribution ranges endemic to the western Balkan Peninsula, an important yet understudied Pleistocene refugium. Our aims were: to test predictions of the ‘refugia‐within‐refugia’ model of strong genetic subdivisions due to population isolation in separate refugia; to explore whether two ecologically divergent species reacted differently to Pleistocene climatic fluctuations; and to test predictions of the displacement refugia model of stronger differentiation among populations in the thermophilic E. tenuifolius compared with the cold‐tolerant E. serpyllifolius. Location The western Balkan Peninsula. Methods We gathered amplified fragment‐length polymorphism (AFLP) data and plastid DNA sequences from two to five individuals from 10 populations of E. serpyllifolius and 22 populations of E. tenuifolius, spanning their entire respective distribution areas. AFLP data were analysed using a Bayesian clustering approach and a distance‐based network approach. Plastid sequences were used to depict relationships among haplotypes in a statistical parsimony network, and to obtain age estimates in a Bayesian framework. Results In E. serpyllifolius, both AFLP and plastid sequence data showed clear geographic structure. Western populations showed high AFLP diversity and a high number of rare fragments. In E. tenuifolius, both markers congruently identified a major phylogeographic split along the lower Neretva valley in central Dalmatia. The most distinct and earliest diverging chloroplast DNA (cpDNA) haplotypes were found further south in the south‐easternmost populations. North‐western populations, identified as a separate cluster by Bayesian clustering, were characterized by low genetic diversity and a low number of rare AFLP markers. Main conclusions Clear evidence for multiple Pleistocene refugia is found not only in the high‐elevation E. serpyllifolius, but also in the lowland E. tenuifolius, despite the lack of obvious dispersal barriers, in line with the refugia‐within‐refugia model. Genealogical relationships and genetic diversity patterns support the hypothesis that cold‐adapted E. serpyllifolius responded to climatic oscillations mostly by elevational range shifts, whereas thermophilic E. tenuifolius did so mainly by latitudinal range shifts, with different phases (and probably extents) of range expansion. In contrast to the displacement refugia hypothesis, the two elevationally differentiated species do not differ in their genetic diversity.