Geographic variation and dispersal history in Fennoscandian populations of two forest herbs

 Carex digitata and Melica nutans are forest understorey herbs with wide European distributions and their northern range margins in Fennoscandia. The species have closely similar habitat requirements, occur in small populations in old forest stands on base-rich to neutral soils and have restricted dispersal abilities at the present day. This study investigates the structure of allozyme variation (12 and 8 loci, respectively) in material of both species (38 and 37 populations, respectively) from throughout southern Sweden and southern Finland. Both species show a relatively low overall genetic diversity (H_T excluding monomorphic loci=0.17 and 0.18, respectively). The hierarchic structuring of allelic diversity in the species is similar, with a relatively high between-population component of diversity (G_ST=0.36 and 0.37, respectively). Neither of the species shows a clear intraspecific pattern of geographic differentiation. The lack of large-scale patterns of geographic differentiation is not consistent with a simple scenario of discrete and independent waves of immigration into Fennoscandia. However, particularly in M. nutans, a group of populations from a lowland belt across southwestern Finland and southern central Sweden is somewhat differentiated from populations to the north and south. A number of rare alleles in both species are widely, but patchily distributed in low frequencies. Hybridization may account for the scattered occurence of some of the rare alleles in Carex digitata, but cannot explain the distribution of rare alleles in Melica nutans. Received July 23, 2001 Accepted December 6, 2001     

Studies in the Melica ciliata – complex: 1. Distribution of allozyme variation within and among individuals, populations and geographic regions

Allozyme variation in 83 European populations of the Melica ciliata/ transsilvanica species complex has been investigated. In spite of a diploid chromosome number, most loci were duplicated and patterns of within-population variation were not explainable unless apomixis or uncommon patterns of chromosomal segregation were assumed. Allelic richness and genetic diversity were very high but most of the variation (55-98%) was due to population differentiation. Geographic patterns were analysed both using phenetic, based on allele frequencies within populations, and cladistic, based on multi-locus genotypes, methods. Both methods congruently recognised three large groups of populations with discrete geographic distributions, in addition to a number of smaller groups. Of the three main groups, one was distributed in eastern and central Europe, one was restricted to western Europe north of the Alps and one was distributed in Iberia, Brittany and along the western shores of the Mediterranean. These groups are likely to have had separate histories but there appears to have been significant gene-flow among them. Among the less distinct groups, it was suggestive that some, e.g. the group containing all populations from the disjunct distribution in the Baltic basin, have been formed by introgression between the three major groups, whereas other deviating populations may represent additional distinct entities.     

Genetic differentiation and speciation in prealpine Cochlearia: Allohexaploid Cochlearia bavarica Vogt (Brassicaceae) compared to its diploid ancestor Cochlearia pyrenaica DC. in Germany and Austria

 Significant geographic partitioning of genetic variation within Cochlearia bavarica was found within populations from Allg?u and SE Bavaria (Germany) exhibiting significant genetic differentiation. It has been demonstrated that allohexaploid C. bavarica evolved via hybridization between diploid C. pyrenaica and tetraploid C. officinalis. Presently, only C. pyrenaica is distributed throughout inland Central Europe. It has been concluded that C. bavarica is of inter- or postglacial origin, and its speciation was not influenced by human activities. Isozyme analysis revealed that there is a correlation between interpopulational genetic distances and geographic distances among C. bavarica populations from both regions, and which is not the case for C. pyrenaica in Germany and Austria. Only high alpine C. excelsa is significantly differentiated among the diploid taxa analysed here. Geographically structured distribution of alleles and their frequencies in C. bavarica populations could not be explained with the distribution of these alleles in C. pyrenaica. The presented findings favour disruption of a former wider distribution area rather than migration of C. bavarica or a polytopic origin of this species. Received April 17, 2001 Accepted February 1, 2002     

Allozyme diversity and genetic structure of marginal and central populations of Corylus avellana L. (Betulaceae) in Europe

Corylus avellana L. (hazel, Betulaceae) is a long-lived, widespread shrub in Europe, having its northern range margin in Fennoscandia and a postglacial history involving range-expansion from refugial areas in southern Europe. In this study, we tested for a relationship between marginality and low within-population genetic diversity by assessing patterns of variation at 14 putatively neutral allozyme loci (comprising 43 putative alleles) within and between 40 natural populations of C. avellana along a north-south transect in Europe. Geographically marginal populations (central Sweden) showed lower levels of within-population diversity than populations in more central regions, as indicated by significant negative correlations between latitude and the percentage of polymorphic loci (r_S=–0.47, P < 0.001), the average number of alleles per locus (r_S=–0.65, P < 0.001), the expected heterozygosity (r_S=–0.19, P < 0.05), and the proportion of distinguishable genotypes (r_S=–0.56, P < 0.001). These patterns, combined with the unusually high between-population component of gene diversity (G_ST=19.7%) and allelic richness (A_ST=24%) in the marginal region, can be attributed to historical bottlenecks during the species postglacial range-expansion, but may also reflect a history of genetic drift in the small, isolated populations occupying the marginal region. Information on the spatial distribution of genotypes provide further support for a role of vegetative reproduction (layering) in the structuring of genetic variation within populations.     

Floral morphology and reproductive success in the orchid Epipactis helleborine: regional and local across-habitat variation

 The terrestrial orchid Epipactis helleborine is a morphologically variable species with a wide distribution in Europe. It is pollinated by social wasps, and most populations show the morphological characteristics of outcrossing species. However, local predominantly selfing subspecies and varieties have been documented from drier habitats. To document geographic variation in floral morphology, ability to produce seeds through autogamy, and reproductive success in E. helleborine, we sampled 13 populations from three geographic regions along a latitudinal gradient of c. 1000 km from northern to southern Sweden. In the southernmost region, populations in dry and mesic habitats were compared. Supplemental hand-pollination was conducted to determine whether among-population variation in fruit set could be explained by differences in the natural level of pollination, and whether any relationship between floral morphology and fruit production could be explained by interactions with pollinators. Bagging experiments showed no evidence of autogamy in any of the study populations. Number of flowers, pollinia removal and fruit set varied significantly among populations but did not differ among regions. Pollinia removal was positively correlated with population size and both pollinia removal and fruit set were lower in dry than in mesic habitats. At the level of the individual plant, the number of pollinia removed increased more rapidly with flower number than did number of fruits produced. The hand-pollination experiment indicated that the positive relationship between number of flowers and fruit production was due to a higher degree of pollen limitation in plants with few flowers than in plants with many flowers. The experiment also showed that variation in the level of pollen limitation could only partly explain variation in fruit set among populations. Received November 6, 2001; accepted April 27, 2002 Published online: December 3, 2002     

Geographic distribution and recombination of genomic fragments on the short arm of chromosome 2 of Arabidopsis thaliana

Abstract: Range expansion from Pleistocene refugia and anthropogenic influences contribute to the present distribution pattern of Arabidopsis thaliana. We scored a genome-wide set of CAPSs and found two markers with an east-west geographic distribution across the Eurasian range of the species. Regions around the two SNPs were sequenced in 98 accessions, including newly collected plants from Middle Asia and Western Siberia. These regions correspond to a gene (∼ 1500 bp) and a non-coding region (∼ 500 bp) 300 kbp apart on chromosome 2. Nucleotide diversities, π, of the two sequenced fragments were 0.0032 and 0.0130. The haplotypes of both sequences belonged to one of two groups: a rather uniform "Asian" and a more variable "European" haplotype group, on the basis of non-disjunct clusters of SNPs. Recombination between "Asian" and "European" haplotypes occurs where they meet. Especially in the "European" haplotype, many rare SNP variants representing independent mutations are scattered among the shared haplotype-specific SNPs. This agrees with previous suggestions of two large haplotype groups in A. thaliana and the post-glacial colonization of central Europe from the east and the west. A clear correlation between climatic factors and the haplotype distribution may reflect the dispersal history rather than local climate adaptation. The pattern of SNP variation within the contiguous sequences explains why only a minority of SNPs selected across the genome show evidence of this geographic pattern.     

Allozyme diversity in relation to geographic distribution and population size inLathyrus vernus (L.) Bernh. (Fabaceae)

Lathyrus vernus (L.) Bernh. is a diploid, long-lived perennial and insect-pollinated herb with no special adaptation to long-distance dispersal. It occurs on neutral soil in deciduous forests throughout western Eurasia. Due to specific habitat preferences,L. vernus has a fragmented distribution with isolated populations. We investigated allozyme variation at eleven loci in 20 populations ofL. vernus from one geographically central region (the Czech Republic and the Slovak Republic) and two geographically marginal regions (southern and central Sweden) in the species present-day distribution. There was a clear differentiation between the three regions and the genetic distance between the populations was highly correlated with geographic distance. The total genetic diversity (H_T) was 0.354. The proportion of genetic diversity due to differentiation between regions, and to differentiation between populations within regions, accounted for 10% each. There was no difference in level of genetic diversity between the three regions. No significant difference in level of genetic diversity was found between small and large populations. The genetic diversity inL. vernus may either be a result of the long generation-time of the species or peculiarities in the post-glacial migration species, e.g. survival only in refugia far east of the sampled populations and/or migration as a continuous process not involving founder-events.     

Past and current gene flow in the selfing, wind-dispersed species Mycelis muralis in western Europe

The distribution of genetic diversity in Mycelis muralis, or wall lettuce, was investigated at a European scale using 12 microsatellite markers to infer historical and contemporary forces from genetic patterns. Mycelis muralis has the potential for long-distance seed dispersal by wind, is mainly self-pollinated, and has patchily distributed populations, some of which may show metapopulation dynamics. A total of 359 individuals were sampled from 17 populations located in three regions, designated southern Europe (Spain and France), the Netherlands, and Sweden. At this within-region scale, contemporary evolutionary forces (selfing and metapopulation dynamics) are responsible for high differentiation between populations (0.34 < F(ST) < 0.60) but, contrary to expectation, levels of within-population diversity, estimated by Nei's unbiased expected heterozygosity (H(E)) (0.24 < H(E) < 0.68) or analyses of molecular variance (50% of the variation found within-populations), were not low. We suggest that the latter results, which are unusual in selfing species, arise from efficient seed dispersal that counteracts population turnover and thus maintains genetic diversity within populations. At the European scale, northern regions showed lower allelic richness (A = 2.38) than populations from southern Europe (A = 3.34). In light of postglacial colonization hypotheses, these results suggest that rare alleles may have been lost during recolonization northwards. Our results further suggest that mutation has contributed to genetic differentiation between southern and northern Europe, and that Sweden may have been colonized by dispersers originating from at least two different refugia.     

Surprising diversity in the Pannonian populations of Marsh Fritillary (Euphydryas aurinia,Lepidoptera: Nymphalidae): Morphometric and molecular aspects

Since genetic variation is the basis of evolutionary potential of a species, its structure needs to be understood. Thus, the aim of this study was to analyze and contrast the structure of genetic and phenotypic variation in the Euphydryas aurinia populations of southeastern central Europe. Genetic variation was studied by two types of molecular genetic markers: mtDNA COI sequences and allozymes. As the great hiatus in the European distribution of E. aurinia is located in the central part of the Carpathian Basin, we expected that the populations East and West to this gap would be highly differentiated. Populations of Central Transdanubia actually represent the easternmost margin of the West European distribution of E. aurinia. In view of the peripheral position of these populations, we supposed to find some genetic sign of local adaptation, as a consequence of diversifying selection and an increased level of fluctuating asymmetry as a result of environmental stress. The analyses of the molecular genetic markers revealed a basic East–West differentiation among the populations of southeastern central Europe which was further structured in the western part of the study area. The results suggested that the genetic differentiation between the two western regions is probably the consequence of diversifying selection. The pattern of phenotypic differentiation among the western populations, however, was different. A geographic cline was revealed (decreasing wing size) toward the eastern margin of the distribution in parallel with increasing fluctuating asymmetry. The conservation inferences of the results are considered.     

High levels of Y-chromosome differentiation among native Siberian populations and the genetic signature of a boreal hunter-gatherer way of life

We examined genetic variation on the nonrecombining portion of the Y chromosome (NRY) to investigate the paternal population structure of indigenous Siberian groups and to reconstruct the historical events leading to the peopling of Siberia. A set of 62 biallelic markers on the NRY were genotyped in 1432 males representing 18 Siberian populations, as well as nine populations from Central and East Asia and one from European Russia. A subset of these markers defines the 18 major NRY haplogroups (A-R) recently described by the Y Chromosome Consortium (YCC 2002). While only four of these 18 major NRY haplogroups accounted for -95% of Siberian Y-chromosome variation, native Siberian populations differed greatly in their haplogroup composition and exhibited the highest phiST value for any region of the world. When we divided our Siberian sample into four geographic regions versus five major linguistic groupings, analyses of molecular variance (AMOVA) indicated higher phiST and phiCT values for linguistic groups than for geographic groups. Mantel tests also supported the existence of NRY genetic patterns that were correlated with language, indicating that language affiliation might be a better predictor of the genetic affinity among Siberians than their present geographic position. The combined results, including those from a nested cladistic analysis, underscored the important role of directed dispersals, range expansions, and long-distance colonizations bound by common ethnic and linguistic affiliation in shaping the genetic landscape of Siberia. The Siberian pattern of reduced haplogroup diversity within populations combined with high levels of differentiation among populations may be a general feature characteristic of indigenous groups that have small effective population sizes and that have been isolated for long periods of time.     

Phylogeography of Scots pine in Europe and Asia based on mtDNA polymorphisms

We analyzed mitochondrial DNA polymorphisms to search for evidence of the genetic structure and patterns of admixture in 124 populations (N = 1407 trees) across the distribution of Scots pine in Europe and Asia. The markers revealed only a weak population structure in Central and Eastern Europe and suggested postglacial expansion to middle and northern latitudes from multiple sources. Major mitotype variants include the remnants of Scots pine at the north-western extreme of the distribution in the Scottish Highlands; two main variants (western and central European) that contributed to the contemporary populations in Norway and Sweden; the central-eastern European variant present in the Balkan region, Finland, and Russian Karelia; and a separate one common to most eastern European parts of Russia and western Siberia. We also observe signatures of a distinct refugium located in the northern parts of the Black Sea basin that contributed to the patterns of genetic variation observed in several populations in the Balkans, Ukraine, and western Russia. Some common haplotypes of putative ancient origin were shared among distant populations from Europe and Asia, including the most southern refugial stands that did not participate in postglacial recolonization of northern latitudes. The study indicates different genetic lineages of the species in Europe and provides a set of genetic markers for its finer-scale population history and divergence inference.     

Colonization history of Scots pine in Eastern Europe and North Asia based on mitochondrial DNA variation

During Quaternary glaciations, the ranges of Northern Eurasia forest species periodically experienced contraction followed by subsequent re-colonizations in the interglacial intervals. However, unlike the broadleaf trees of temperate forests, taiga species seem not to have retreated fully to southern regions in unfavorable periods and possibly survived at mid-latitudes in multiple refugia. Here, we report a study of genetic variation of three mitochondrial DNA markers in 90 populations of Scots pine (Pinus sylvestris) located from Eastern Europe to Eastern Siberia. The geographic distribution of seven mitotypes demonstrated the split between western and eastern populations approximately along the 38th meridian. Genetic diversity in the western part was significantly higher than in the eastern one. Five mitotypes were western- and one eastern-specific. One mitotype was common in both regions, but in the eastern part it occurred only in the South Urals and adjacent areas. The geographic structure in the mitotype distribution supports a hypothesis of post-glacial re-colonization of the studied territory from the European and Ural refugia.     

Modelling range shifts and assessing genetic diversity distribution of the montane aquatic mayfly Ameletus inopinatus in Europe under climate change scenarios

Genetic diversity is one of the most important criteria to identify unique populations for conservation purposes. In this study we analyze the genetic population structure of the endangered montane mayfly Ameletus inopinatus in its European range. The species is restricted to unpolluted cold-water streams, and exhibits an insular distribution across highlands of Central Europe and a more continuous distribution across Fennoscandia and Northern Euro-Siberia. We genotyped 389 individuals from 31 populations for eight highly polymorphic microsatellite loci to investigate genetic diversity and population structure within and among European mountain ranges. Genetic diversity of A. inopinatus decreases along an east?Cwest gradient in Central Europe and along a north?Csouth gradient in Fennoscandia, respectively. Centres of exceptionally high genetic diversity are located in the Eastern Alps (Andertal Moor, Austria), the High Tatra, the Beskides, the Sudety Mountains and the Eastern German Highlands. Species distribution modelling for 2080 projects major regional habitat loss, particularly in Central Europe mountain ranges. By relating these range shifts to our population genetic results, we identify conservation units primarily in Eastern Europe, that if preserved would maintain high levels of the present-day genetic diversity and continue to provide long-term suitable habitat under future climate warming scenarios.     

GENETIC AND MORPHOMETRIC DIVERGENCE IN ANCESTRAL EUROPEAN AND DESCENDENT NEW ZEALAND POPULATIONS OF CHAFFINCHES (FRINGILLA COELEBS)

Descendent populations of chaffinches (Fringilla coelebs) introduced to New Zealand about 120 years ago were compared with “ancestral” populations in northern Europe and with those in a broader region of Europe (including Iberia) using protein electrophoresis at 42 loci and 12 skeletal measurements. The New Zealand populations exhibit very small scale differentiation in genetics (F_st = 0.040) and morphometrics, and the haphazard pattern of among-population variation does not align with environmental variation nor is it predicted by the geographic proximity of populations. Thus random drift is implicated in the differentiation among the descendent populations. The New Zealand chaffinches have diverged only slightly in morphometrics from an extant population in southern England, and constant heritability rate tests suggest that random drift alone could account for this small shift. In sharp contrast, the European populations are subdivided genetically (F_st = 0.222) and morphometrically, and this subdivision coincides with the Pyrenees mountains between Iberia and northern Europe which act as a barrier to gene flow between these regions. Iberian populations have smaller skulls and longer wings on average than northern European populations and are characterized by high frequencies of alternative common alleles at Ada and Np. Within both the Iberian and northern European regions, however, populations are effectively panmictic in protein-encoding genes, indicating that homogenizing gene flow is apparently extensive enough to prevent among-population differentiation in allozymes by drift. Variation in body size as represented by PC I is related to environmental productivity across Europe, unlike in New Zealand. These observations jointly suggest that longer term adaptive differentiation via selection for optimal body size has evolved in Europe. Because multilocus evolution is expected to proceed slowly in populations subject to the opposing forces of selection and homogenizing gene flow, I argue that local adaptation within “ancestral” populations in northern Europe may still be evolving.     

Cranial variation in the European badger Meles meles (Carnivora,Mustelidae) in Scandinavia

Morphometric variation in 30 craniometric characters of 465 skulls of the European badgers (Meles meles) from across Europe was analysed. Multivariate analyses revealed that the populations from Norway, Sweden, and Finland differ from other European populations in having smaller skulls. The analyses also revealed significant differences between the ‘south‐western Norwegian’ and ‘main Fennoscandian’ forms. On average, badgers from south‐west Norway were smaller than those of the remaining Fennoscandia. Morphological differences between the ‘south‐western Norwegian’ and ‘main Fennoscandian’ populations of M. meles suggest a possible in situ semisympatric divergence since the beginning of the Holocene warming, or a complex history of two groups involving at least two colonization routes. The small‐sized Scandinavian badgers may be close to the ancestral form that used to be widespread in Denmark and throughout Europe. The animals from south‐west Norway may instead be descendants of ancestors that were the first to penetrate the southern parts of the Scandinavian Peninsula. The ‘main Fennoscandian’ badgers are likely to have been the descendants of the second wave of recolonization of Scandinavia. Specifically, they might have colonized the Scandinavian Peninsula from the east after the last glaciation.     

Genetically diverse but with surprisingly little geographical structure: the complex history of the widespread herb Carex nigra (Cyperaceae)

Aim Based on extensive range‐wide sampling, we address the phylogeographical history of one of the most widespread and taxonomically complex sedges in Europe, Carex nigra s. lat. We compare the genetic structure of the recently colonized northern areas (front edge) and the long‐standing southern areas (rear edge), and assess the potential genetic basis of suggested taxonomic divisions at the rank of species and below. Location Amphi‐Atlantic, central and northern Europe, circum‐Mediterranean mountain ranges, central Siberia, Himalayas. Methods A total of 469 individuals sampled from 83 populations, covering most of the species’ range, were analysed with amplified fragment length polymorphism (AFLP) and chloroplast DNA (cpDNA) markers. Bayesian clustering, principal coordinates analysis, and estimates of diversity and differentiation were used for the analysis of AFLP data. CpDNA data were analysed with statistical parsimony networks and maximum parsimony and Bayesian inference of phylogenetic trees. Results Overall genetic diversity was high, but differentiation among populations was limited. Major glacial refugia were inferred in the Mediterranean Basin and in western Russia; in addition, there may have been minor refugia in the North Atlantic region. In the southern part of the range, we found high levels, but geographically quite poorly structured genetic diversity, whereas the levels of genetic diversity varied among different areas in the north. North American populations were genetically very similar to the European populations. Main conclusions The data are consistent with extensive gene flow, which has obscured the recent history of the taxon. The limited differentiation in the south probably results from the mixing of lineages expanding from several local refugia. Northward post‐glacial colonization resulted in a leading‐edge pattern of low diversity in the Netherlands, Belgium, Scotland and Iceland, whereas the observed high diversity levels in Fennoscandia suggest broad‐fronted colonization from the south as well as from the east. The patterns found in the American populations are consistent with post‐glacial colonization, possibly even with anthropogenic introduction from Europe. Our data also suggest that the tussock‐forming populations of C. nigra, often referred to as a distinct species (Carex juncella), represent an ecotype that has originated repeatedly from different populations with creeping rhizomes.     

Geographical distribution,genetic diversity and social organization of a new European termite, <Emphasis Type="Italic">Reticulitermes urbis</Emphasis> (Isoptera: Rhinotermitidae)

Reticulitermes urbis is a recently described termite species that has probably been introduced into Western Europe where it has been found exclusively in urban areas. However, little is known about the geographic distribution and origin of R. urbis. This study was undertaken to determine whether this species was introduced from the Balkans. A parsimony network did not show any association between mtDNA haplotypes and geographic regions suggesting that western European populations were the result of human-mediated dispersion. Variation patterns of the COI and COII regions as well as microsatellites showed that the genetic diversity of Western European colonies was lower than for colonies collected in the Balkans, suggesting that the introduced populations suffered from a founder effect. As observed in the introduced populations of R. flavipes, all colonies of R. urbis had an extended-family structure with several reproductives. These results support the scenario that this termite was introduced into Western Europe.     

World distribution of female flight and genetic variation in Lymantria dispar (Lepidoptera: Lymantriidae)

Female gypsy moths, Lymantria dispar L., from 46 geographic strains were evaluated for flight capability and related traits. Males from 31 of the same strains were evaluated for genetic diversity using two polymorphic cytochrome oxidase I mitochondrial DNA restriction sites, the nuclear FS1 marker, and four microsatellite loci. Females capable of strong directed flight were found in strains that originated from Asia, Siberia, and the northeastern parts of Europe, but flight capability was not fixed in most strains. No flight-capable females were found in strains from the United States or southern and western Europe. Wing size and musculature were shown to correlate with flight capability and potentially could be used in predicting female flight capability. The mtDNA haplotypes broadly separated the gypsy moth strains into three groups: North American, European/Siberian, and Asian. Specific microsatellite or FS1 alleles were only fixed in a few strains, and there was a gradual increase in the frequency of alleles dominant in Asia at both the nuclear and microsatellite loci moving geographically from west to east. When all the genetic marker information was used, 94% of the individuals were accurately assigned to their broad geographic group of origin (North American, European, Siberian, and Asian), but female flight capability could not be predicted accurately. This suggests that gene flow or barriers to it are important in determining the current distribution of flight-capable females and shows the need for added markers when trying to predict female flight capability in introduced populations, especially when a European origin is suspected.     

Regional and local spatial genetic structure of Siberian primrose populations in Northern Europe

We have investigated the local and regional scale genetic structure of Siberian primrose (Primula nutans) populations in Northern Europe. The genetic diversity and structure of fifteen populations sampled from the Bothnian Bay in Finland, the Barents Sea in Norway and the White Sea in Russia were assessed using eleven microsatellite markers. We investigated the distribution of genetic variation within and between populations, and studied the local genetic structure using spatial autocorrelation analysis. We found very low genetic and allelic diversity in the Bothnian Bay and Barents Sea populations, and only slightly higher in the White Sea population. The level of genetic differentiation between the regions was very high, whereas differentiation between the populations within the regions was moderate. We found no spatial structuring of populations in any region suggesting efficient dispersal on a local scale. Clonal reproduction seemed to have no effect on genetic structure.     

Loss of genetic variation in geographically marginal populations of Atriplex tatarica (Chenopodiaceae)

BACKGROUND AND AIMS: Genetic variability was estimated for Atriplex tatarica from 25 populations in the Czech Republic. Since its north-western range margin is in central Europe, a relationship between marginality and low within-population genetic diversity was tested in accordance with the Central-Marginal Model. METHODS: Population genetic diversity was expressed by assessing patterns of variation at 13 putatively neutral allozyme loci (comprising 30 putative alleles) within and between 25 natural populations of A. tatarica along a north-west-south-east transect in the Czech Republic. KEY RESULTS: Atriplex tatarica is a species of human-made habitats with a mixed mating system and wide geographic distribution. Overall, A. tatarica displayed moderate levels of genetic diversity in comparison with other herbaceous plants. The percentage of loci that were polymorphic was 47.1%, with average values of 1.55, 0.151 and 0.155 for the average number of alleles per polymorphic locus (A), observed heterozygosity (Ho) and expected heterozygosity (He), respectively. There was only weak evidence of inbreeding within populations (FIS=0.031) and significant population differentiation (FST=0.214). Analysis of the data provides no evidence for isolation-by-distance for the whole study area. However, Mantel tests were highly significant for the marginal Bohemian region and non-significant for the central Moravian region. While northern populations of A. tatarica showed significantly lower allelic richness (A=1.462) than populations from the southern part of the study area (A=1.615), they did not differ in observed heterozygosity (Ho), gene diversity (HS), inbreeding within populations (FIS) or population differentiation (FST), despite generally lower values of particular genetic measurements in the marginal region. CONCLUSIONS: Genetic diversity, with the exception of allelic richness, was not significantly lower at the margins of the species' range. This, therefore, provides only weak support for the predictions of the Central-Marginal Model.