Were the main mountain ranges in the Korean Peninsula a glacial refugium for plants? Insights from the congeneric pair Lilium cernuum – Lilium amabile

The main Korean mountain range (the so-called “Baekdudaegan”), which stretches from north to south across most of the country, has been thought to harbor glacial refugia for boreal plant species, where they likely found relatively stable habitats and maintained large population sizes. Under this scenario, high levels of genetic variation and low or moderate degree of differentiation among populations within these species were expected. To test this hypothesis, we examined levels of allozyme diversity (14 loci) in eight populations of the boreal herb Lilium cernuum, which in Korea occurs largely along the Baekdudaegan and, as a reference, in eight populations of its congener Lilium amabile, a temperate species that is distributed on lower hillsides in peripheral regions of the Baekdudaegan. L. cernuum harbored higher levels of genetic variation within populations than L. amabile (%P = 49.1 vs. 25.0, A = 1.71 vs. 1.34, and H_e = 0.159 vs. 0.048). Genetic differentiation among populations was low for both species (F_ST = 0.119 and 0.014 for L. cernuum and L. amabile, respectively). A series of historical and ecological factors may explain the contrasting levels of genetic diversity between L. cernuum and L. amabile: occurrence within the main ranges of the Baekdudaegan (enduring the glacial periods in macrorefugia) vs. low elevation peripheral areas (in microrefugia) and shade-tolerant vs. shade-intolerant. This study, as well as previous population genetics studies, strongly suggests that the Baekdudaegan merits high priority for conservation given its proposed role as glacial refugia for montane species.     

Large effective population sizes and high levels of gene flow between subpopulations of Lilium cernuum (Liliaceae)

The Baekdudaegan, a mountain range that runs north to south along the Korean Peninsula, has been suggested to harbor important glacial refugia for boreal and temperate plant species. A series of allozyme-based genetic studies supports this trend. A large effective population size (N_e) is suggested as one of major factors contributing to maintaining moderate or high levels of within-population genetic variation in these plant species. To test this hypothesis, we examined the levels and patterns of allozyme diversity, tested recent bottlenecks, and estimated recent migration rates in 10 subpopulations (collected within a distance of ca. 640 m) of the boreal Lilium cernuum at Mt. Deokhang, in the central part of the Baekdudaegan. We found high levels of within-population genetic variation as well as a low between-population genetic differentiation (H_e = 0.206 and F_ST = 0.019). Based on the F_ST estimate and mean recent migration rate, we approximately calculated a total effective population size of 508 across 10 subpopulations. Consistent with this, we found no evidence of recent bottlenecks in the subpopulations. This study reveals that subpopulations of L. cernuum at Mt. Deokhang are effectively large (on the order of hundreds), and that high levels of gene flow occur among them, probably due to the species' high potential for seed dispersal. These demographic and life-history traits, coupled with its high levels of genetic diversity, suggests that this cold-adapted species would have found large refugial areas in these mountains (i.e., macrorefugia) during the Last Glacial Maximum.     

Genetic diversity in three species of Forsythia (Oleaceae) endemic to Korea: Implications for population history,taxonomy, and conservation

As the mountains in temperate regions have been hypothesized as refugia for boreal and temperate plants during the Last Glacial Maximum, one would expect high within-population genetic variation and low or moderate among-population differentiation for those species occurring there. We selected Forsythia ovata and Forsythia saxatilis, endemic to limestone mountains of Korea, to test the scenario that limestone ranges would also have acted as refugia. We undertook a population genetic analysis using 14 putative allozyme loci of the two species and the widely cultivated Forsythia koreana. We found relatively high levels of genetic diversity and low to moderate among-population differentiation in F. ovata and F. saxatilis, which are consistent with the proposed scenario. Allozyme data revealed that F. ovata and F. saxatilis are likely conspecific. As many populations of F. ovata and F. saxatilis have experienced dramatic decreases in their size, a comprehensive conservation program is urgently needed.     

Population genetic structure of a widespread coniferous tree, Taxodium distichum [L.] Rich. (Cupressaceae), in the Mississippi River Alluvial Valley and Florida

Studies of genetic variation can elucidate the structure of present and past populations as well as the genetic basis of the phenotypic variability of species. Taxodium distichum is a coniferous tree dominant in lowland river flood plains and swamps of the southeastern USA which exhibits morphological variability and adaption to stressful habitats. This study provides a survey of the Mississippi River Alluvial Valley (MAV) and Florida to elucidate their population structure and the extent of genetic differentiation between the two regions and sympatric varieties, including bald cypress (var. distichum) and pond cypress (var. imbricatum). We determined the genotypes of 12 simple sequence repeat loci totaling 444 adult individuals from 18 natural populations. Bayesian clustering analysis revealed high levels of differentiation between the MAV and the Florida regions. Within the MAV region, there was a significant correlation between genetic and geographical distances. In addition, we found that there was almost no genetic differentiation between the varieties. Most genetic variation was found within individuals (76.73?%), 1.67?% among individuals within population, 15.36?% among populations within the regions, and 9.23?% between regions within the variety. Our results suggest that (1) the populations of the MAV and the Florida regions are divided into two major genetic groups, which might originate from different glacial refugia, and (2) the patterns of genetic differentiation and phenotypic differentiation were not parallel in this species.     

Ice-age isolation,postglacial hybridization and recent population bottlenecks shape the genetic structure of Meum athamanticum in Central Europe

Phylogeographic analyses can help to reveal the refugial structure of plants during and after the ice ages, but the detailed history of regional refugial isolation and differentiation in Central Europe is still poorly understood. A recent study of Meum athamanticum in its total range of occurrences revealed persistence of this temperate montane plant species in Central Europe north of the Alps, without going into details. We therefore aimed to study differentiation and migration processes of this plant species in more detail throughout Central Europe. We used high resolution amplified fragment length polymorphisms (AFLP) markers and analyzed 210 plant individuals of 14 Central European populations with three pairs of primer combinations (128 loci, 111 of which polymorphic). The data show genetic differentiation and varying levels of molecular diversity within populations and groups of populations. Altogether, the studied populations did not show a gradient in molecular variation along presumptive postglacial migration routes across Central Europe. Rather, they reveal a genetic division into seven major groups. Four of them are characterised by high genetic diversity, private fragments and higher than average number of rare and sparse fragments, leading to the assumption that they are descendants of independent populations which survived in glacial refugia. In combination with information from paleoclimate and paleovegetation, it is likely that microclimatically favoured habitats at (i) the eastern flank of the Black Forest, (ii) the southern margin of the Cologne basin, (iii) the foothills of the Erzgebirge, and (iv) the foothills of the Jura Mountains acted as sources for the postglacial recolonisation of this species to the other mountains of Central Europe. As some of the populations analysed show intermixed gene-pools (i.e. including genetic information from different groups) and partly have exceptionally high genetic diversity, but no private and only relatively few rare or sparse fragments, they might represent contact zones. On the other hand, genetic pauperization and isolation of two other populations in connection with extremely small population sizes and unfavourable habitat conditions seem to reflect recent bottlenecks. Consequently, the genetic structure of M. athamanticum in Central Europe is shaped by (i) extra-Mediterranean glacial refugia in situ, (ii) following postglacial hybridization along emerging contact zones and (iii) genetic bottlenecks in thereafter isolated small populations. All results provide evidences for small scale migration of the species between Central European valleys and surrounding highlands. Therefore, our study provides molecular evidence for both climate dependent wide ranging periglacial tabula rasa, but some small refugia in locally buffered areas. We hereby show that the environmental heterogeneity of cold stage landscapes in Central Europe is generally underestimated.     

Glacial refugia and modern genetic diversity of 22 western North American tree species

North American tree species, subspecies and genetic varieties have primarily evolved in a landscape of extensive continental ice and restricted temperate climate environments. Here, we reconstruct the refugial history of western North American trees since the last glacial maximum using species distribution models, validated against 3571 palaeoecological records. We investigate how modern subspecies structure and genetic diversity corresponds to modelled glacial refugia, based on a meta-analysis of allelic richness and expected heterozygosity for 473 populations of 22 tree species. We find that species with strong genetic differentiation into subspecies had widespread and large glacial refugia, whereas species with restricted refugia show no differentiation among populations and little genetic diversity, despite being common over a wide range of environments today. In addition, a strong relationship between allelic richness and the size of modelled glacial refugia (r² = 0.55) suggest that population bottlenecks during glacial periods had a pronounced effect on the presence of rare alleles.     

Structure of Pinus nigra Arn. populations in Bulgaria revealed by chloroplast microsatellites and terpenes analysis: Provenance tests

Pinus nigra is a forest and low elevation mountain species found around the Mediterranean Sea that has had its distribution reduced and fragmented by anthropogenic disturbance. Due to commercial interest it is currently being replanted, however, the genetic structure of populations is little known and current planting strategies could threaten its genetic diversity. In the present study we investigated the genetic structure and genetic diversity of P. nigra populations in Bulgaria using chloroplast microsatellite markers and terpene analysis. Nine provenances were chosen throughout the species' range in Bulgaria. Following DNA extraction, chloroplast microsatellite (cpSSR) loci were surveyed using three primer pairs. Between 5 and 9 size variants were identified at each locus. A total of 22 size variants at the 3 loci were identified, that were combined in 68 different haplotypes, of which 7 represent 39.81% of the genetic structure. AMOVA analysis revealed that 6.06% of the variation was found among populations, while 93.94% was expressed within populations. The cpSSR analysis divided European Black pine populations into four groups, the first represented by populations located the eastern Rhodopes, Sr. Gora and St. Planina mountains, while the second group is primarily located in the Phodopes and Slavianca mountains. The populations from Pirin and Osogovo mountains show different genetic patterns. Terpene analysis revealed that most of the monoterpene pool in P. nigra was accounted for by α-pinene followed by β-pinene. The presence of four distinct terpene groups is not consistent with physical distances between populations, and a similar non-significant correlation between genetic distance determined by chloroplast microsatellites analysis and chemotype distance (determined by terpenes) was observed. Our results suggest that the structural pattern of genetic diversity of cpDNA in European Black pine populations is the consequence of historical biogeographic processes.     

Effects of life-history traits and species distribution on genetic structure at maternally inherited markers in European trees and shrubs

Aim To examine relationships between life‐history traits, ecological and chorological characteristics of woody plant species and patterns of genetic differentiation among populations as assessed by chloroplast DNA (cpDNA) markers, and to compare them with patterns previously described from nuclear markers. Location Europe. Methods Data on cpDNA variation were compiled for 29 temperate European broad‐leaved tree and shrub species. Six qualitative and three quantitative characters of the species were tested for their relationship with two parameters of genetic population differentiation (G_ST and N_ST). Both direct species comparisons and phylogenetically independent contrast analyses were performed. Results When the phylogeny was not taken into account, five characters were significantly related to levels of population differentiation. The relationship disappeared in all but two cases (distribution type and seed mass) when analyses controlled for phylogenetic relationships among species. Main conclusions The correlation between distribution type (boreal‐temperate or temperate) and cpDNA differentiation of temperate European woody plant species suggests that their Quaternary history, in particular the location and isolation of their glacial refugia, is an important determinant of their present‐day level of genetic structure. By contrast, the relationship between life‐history traits and genetic differentiation at maternally inherited markers is weaker, especially when phylogenetic effects are controlled for.     

Phylogeography of the heathers Erica arborea and E. trimera in the afro-alpine ‘sky islands’ inferred from AFLPs and plastid DNA sequences

The ericaceous vegetation zone of the unique and highly fragmented afro-alpine environment in the eastern African high mountains is typically dominated by the heather Erica arborea, often in combination with its close relative E. trimera. Both species are shrubs or small trees with tiny seeds, potentially capable of dispersal by wind over long distances. While E. arborea is widely distributed in Africa, the Middle East and Europe, E. trimera is endemic to the afro-alpine region where it is restricted to higher altitudes than E. arborea. We used Amplified Fragment Length Polymorphisms (AFLPs) and variation in non-coding plastid DNA sequences to test whether these two morphologically and ecologically very similar species display similar phylogeographic patterns in the afro-alpine region. We predict that the more high-altitudinal E. trimera shows more distinct genetic structuring than E. arborea, because dispersal of the latter may have been facilitated by formation of interglacial forest bridges between mountains. Based on extensive field sampling in most of the high mountains of Ethiopia and East Africa, we show that the two species are clearly distinct at AFLP and plastid DNA loci. Both showed low levels of overall AFLP diversity, suggesting bottlenecking in small refugial populations during unfavourable climatic periods. However, their genetic structuring and inferred phylogeographic histories were conspicuously different. The more high-altitudinal E. trimera consisted of three to four distinct AFLP groups, which also had different plastid DNA haplotypes and different geographic distributions, suggesting long-term restriction to several refugia (at least one in Ethiopia and two in East Africa). In contrast, E. arborea showed little geographic structuring at AFLP loci and only a single, widespread plastid DNA haplotype, which may suggest recent colonization of the entire study area from a single source population, likely via a combination of gradual expansion via forest bridges and long-distance dispersals. The source population of E. arborea may be situated in (or north of) Ethiopia, which harbours most genetic diversity.     

Importance of demographic history for phylogeographic inference on the arctic–alpine plant Phyllodoce caerulea in East Asia

Arctic–alpine plants have enormous ranges in the Northern Hemisphere. Phylogeographic studies have provided insights into their glacial survival as well as their postglacial colonization history. However, our understanding of the population dynamics of disjunct alpine populations in temperate regions remains limited. During Pleistocene cold periods, alpine populations of arctic–alpine species in East Asia were either connected to an ice-free Beringia refugium or they persisted with prolonged isolation after their establishment. To estimate which of these scenarios is more likely, we elucidated the genetic structure of Phyllodoce caerulea (Ericaceae) in Beringia and northern Japan, East Asia. Sequence variation in multiple nuclear loci revealed that P. caerulea can be distinguished into northern and southern groups. A demographic analysis demonstrated that the north–south divergence did not predate the last glacial period and detected introgression from Phyllodoce aleutica, relative widely distributed in East Asia, exclusively into the southern group. Therefore, although there has been genetic divergence between northern Japan and Beringia in P. caerulea, the divergence is unlikely to have resulted from their prolonged geographic separation throughout several cycles of glacial and interglacial periods. Instead, our study suggests that the introgression contributed to the genetic divergence of P. caerulea and that the range of P. caerulea was plausibly connected between northern Japan and Beringia during the last glacial period. Overall, our study not only provides a biogeographic insight into alpine populations of arctic–alpine plants in East Asia but also emphasizes the importance of careful interpretation of genetic structure for inferring phylogeographic history.     

Effect of historical factors on genetic variation in three terrestrial Cephalanthera species (Orchidaceae) with different breeding system on the Korean Peninsula

Previous studies have shown that levels of genetic diversity in species of the genus Cephalanthera covary with the breeding system. In the southern part of the Korean Peninsula, the three self‐compatible terrestrial orchids Cephalanthera erecta, C. falcata and C. longibracteata flower synchronously in sympatric populations. The food‐deceptive C. falcata with bright yellow flowers is predominantly outcrossing, whereas autogamy is the dominant strategy in both C. erecta and C. longibracteata, whose white flowers do not open fully. We examined genetic diversity (by means of allozymes) of the three species in sympatric populations (600 × 600 m area) in the Yeonwhasan Provincial Park (YPP) and in non‐sympatric populations outside YPP, South Korea. Thirteen out of 20 putative loci were variable across the three species, but there was a complete lack of allozyme variation within each species and we found no evidence of hybridisation. Our results suggest that historical factors, i.e. the Quaternary climate oscillations, have played a major role in determining levels of genetic diversity in the three Cephalanthera species. The Korean populations of C. erecta (a warm‐temperate/temperate element) and C. falcata (a warm‐temperate element) may have been established by a single introduction from a genetically depauperate ancestral population, likely located outside the Korean Peninsula. On the other hand, since C. longibracteata is a boreal/temperate element, it may have survived the Last Glacial Maximum in microrefugia located in low elevation regions within the Peninsula where it has been subjected to population bottlenecks reducing its genetic diversity.     

Molecular evidence for glacial expansion and interglacial retreat during Quaternary climatic changes in a montane temperate pine (Pinus kwangtungensis Chun ex Tsiang) in southern China

It has been suggested that the eastern Asian temperate flora have responded to Quaternary climatic changes in a different way compared with temperate plants in Europe and Northern America. However, knowledge about their phylogeographic structure and evolutionary history is still limited. In this study we investigated mitochondrial DNA variation in 17 populations of Pinus kwangtungensis, a five-needled pine inhabiting in isolated mountains of southern China and northern Vietnam. A total of ten mitochondrial haplotypes (mitotypes) were characterized by the polymorphisms of two fragments (cox-1-2 and nad7 intron1), and total genetic diversity was high (h _T = 0.847). The construction of phylogenetic relationships of the ten mitotypes detected three major, well-distinct clades, largely corresponding to four population groups identified by SAMOVA analysis. SAMOVA also indicated that most genetic variance should be attributed to among-group differentiation (F _CT = 0.868), consistent with the substantial genetic structure found within P. kwangtungensis (G _ST = 0.751). The genetic distances of P. kwangtungensis weakly but significantly correlated with geographical distances (R = 0.228, P = 0.03), revealing a pattern of isolation-by-distance. Demographic analysis did not detect any bottleneck events in the recent history of P. kwangtungensis. These results clearly suggested that there were three major refugia for this montane temperate conifer during warm stages (along with other minor refugia), and that the species would have tracked Quaternary climatic changes by expanding to nearby lowlands in the glacial periods, and by retreating to mountaintops (the refugia) during interglacial warmer stages, experiencing fragmentation and isolation among refugia.     

Population genetic differentiation of Schisandra chinensis and Schisandra sphenanthera as revealed by ISSR analysis

Schisandra chinensis (Turcz.) Baill. and Schisandra sphenanthera Rehd. et Wils. are well-known Chinese medicinal plants. The population genetic variation of the two species was studied using inter simple sequence repeat (ISSR) molecular markers. High levels of genetic diversity are revealed in both S. chinensis (P = 88.36%, h = 0.2894, I = 0.4396) and S. sphenanthera (P = 84.09%, H = 0.2782, I = 0.4280). However, the population genetic differentiation is significantly different between the two species. The S. sphenanthera harbors as high as 27% of the genetic variation among populations but 73% within populations, whereas in S. chinensis 17% of the genetic variation occurs among populations and 83% within populations. Both significant (P < 0.05) heterozygosity excess and shifted mode of allele frequency distribution are detected in four out of six populations of S. chinensis and one out of five populations of S. sphenanthera, suggesting the occurrence of recent population bottlenecks in the two species. The different patterns of genetic variation in S. chinensis and S. sphenanthera are discussed in relation to their differences in pollination mechanism, geographic distribution and historical events, and the level of gene flow and genetic drift.     

Spatial patterns of genetic diversity across European subspecies of the mountain hare, Lepus timidus L

Fossil evidence shows that populations of species that currently inhabit arctic and boreal regions were not isolated in refugia during glacial periods, but instead maintained populations across large areas of central Europe. These species commonly display little reduction in genetic diversity in northern areas of their range, in contrast to many temperate species. The mountain hare currently inhabits both temperate and arctic-boreal regions. We used nuclear microsatellite and mtDNA sequence data to examine population structure and alternate phylogeographic hypotheses for the mountain hare, that is, temperate type (lower genetic diversity in northern areas) and arctic-boreal type (high northern genetic diversity). Both data sets revealed concordant patterns. Highest allelic richness, expected heterozygosity and mtDNA haplotype diversity were identified in the most northerly subspecies, indicating that this species more closely maps to phylogeographic patterns observed in arctic-boreal rather than temperate species. With regard to population structure, the Alpine and Fennoscandian subspecies were most genetically similar (F(ST) approximately 0.1). These subspecies also clustered together on the mtDNA tree and were assigned with highest likelihood to a common Bayesian cluster. This is consistent with fossil evidence for intermediate populations in the central European plain, persisting well into the postglacial period. In contrast, the geographically close Scottish and Irish populations occupied separate Bayesian clusters, distinct clades on the mtDNA maximum likelihood tree and were genetically divergent from each other (F(ST) > 0.4) indicating the influence of genetic drift, long isolation (possibly dating from the late glacial era) and/or separate postglacial colonisation routes.     

Genetic diversity in the two endangered endemic species Kirengeshoma koreana (Hydrangeaceae) and Parasenecio pseudotaimingasa (Asteraceae) from Korea: Insights into population history and implications for conservation

As mountains have been hypothesized as harboring important Quaternary refugia for plants, one would expect high within-population genetic variation and low or moderate among-population differentiation for those species occurring there. We selected Kirengeshoma koreana and Parasenecio pseudotaimingasa, endemic to mountains of Korea to test the scenario that the main mountain ranges of the Peninsula would also have acted as refugia. We undertook a population genetic analysis using 15 and 12 putative allozyme loci of K. koreana and P. pseudotaimingasa, respectively. We found contrasting levels of genetic diversity in the two species; extremely low within-population genetic variation and high among-population divergence in K. koreana and high within-population genetic variation and moderate among-population divergence in P. pseudotaimingasa. We can conclude that, whereas Korean mountains would have provided large refugial areas (i.e., ‘macrorefugia’) for P. pseudotaimingasa, K. koreana would have endured the Quaternary climate oscillations in small, isolated populations (i.e., ‘microrefugia’). Given the lack of genetic diversity and the extremely low number of populations and individuals of K. koreana, a comprehensive conservation program is urgently needed for this rare and critically endangered species.     

Comparison of the extent of genetic variation of Vallisneria natans and its sympatric congener V. spinulosa in lakes of the middle-lower reaches of the Yangtze River

Vallisneria natans and Vallisneria spinulosa are two morphologically very similar and sympatrically dominant submerged macrophytes in lakes of the middle-lower reaches of the Yangtze River. Genetic variation was compared based on a total of 196 individuals from six V. natans populations and 201 individuals from seven V. spinulosa populations. Using eight ISSR primers, a total of 139 and 129 DNA fragments were generated with 121 being polymorphic in V. natans and 99 in V. spinulosa. The two species maintained higher genetic variation both at the species and population levels in comparison with other aquatic macrophytes. A higher level of genetic diversity among populations was found in V. natans than in V. spinulosa: the percentage of polymorphic loci (PPL) in V. natans was 52-62% vs. 38-47% in V. spinulosa; gene diversity (H) was 0.21 in V. natans vs. 0.17 in V. spinulosa.Both an analysis of molecular variance (AMOVA) and F-estimation (F_ST) showed that most of the total genetic variation resided within populations of both species (AMOVA: 85% and 80%; F_ST: 0.132 and 0.202), indicating low genetic differentiation between populations. Principal coordinates analysis (PCA) indicated evident gene flow between populations of both species. The outcrossing reproductive mode and pervasive gene flow might have played important roles in maintaining high genetic diversity and in shaping low population differentiation of the two Vallisneria species, while the extent of clonal growth might account for the different levels of population divergence between them.     

Genetic diversity and inter-specific relations of western Mediterranean relic Abies taxa as compared to the Iberian A. alba

Several Abies species are currently present in the Mediterranean region and most of them are endemic taxa and tertiary relicts. Using six nuclear microsatellites, we studied the genetic structure and inter-specific relationships among West Mediterranean firs, A. pinsapo (Spain), A. maroccana and A. tazaotana (Morocco). Based on the hypothesis that A. pinsapo could historically exchange genes with A. alba growing in the Pyrenees via secondary contact, we investigated the level of genetic admixture between these species using a Bayesian approach. The studied populations showed moderate genetic diversity (mean H_E = 0.598) and a high level of genetic differentiation (F_ST = 0.225) that was especially pronounced between A. alba and the African firs. All populations experienced a strong bottleneck effect that was likely induced by climatic changes occurring in the West Mediterranean during the last glacial cycle and the Holocene. According to Bayesian clustering, both African taxa grouped together in a single cluster, the two A. pinsapo populations formed a second cluster, and two additional clusters were detected within A. alba. Our results indicate that A. tazaotana is genetically very close to A. maroccana, and hence these two taxa should probably not be considered as separate species. We found no genetic admixture between A. pinsapo and A. alba and only minor between A. pinsapo and the African fir populations suggesting an isolation effect of the Gibraltar Strait. Current limited distributions of firs in the Mediterranean region together with changing climate may lead to further deterioration of the genetic diversity levels. Hence, future efforts should focus on monitoring the demography and genetic threats to existing populations.     

Unravelling genetics at the top: mountain islands or isolated belts?

Background and Aims

In mountain plant populations, local adaptation has been described as one of the main responses to climate warming, allowing plants to persist under stressful conditions. This is especially the case for marginal populations at their lowest elevation, as they are highly vulnerable. Adequate levels of genetic diversity are required for selection to take place, while high levels of altitudinal gene flow are seen as a major limiting factor potentially precluding local adaptation processes. Thus, a compromise between genetic diversity and gene flow seems necessary to guarantee persistence under oncoming conditions. It is therefore critical to determine if gene flow occurs preferentially between mountains at similar altitudinal belts, promoting local adaptation at the lowest populations, or conversely along altitude within each mountain.

Methods

Microsatellite markers were used to unravel genetic diversity and population structure, inbreeding and gene flow of populations at two nearby altitudinal gradients of Silene ciliata, a Mediterranean high-mountain cushion plant.

Key Results

Genetic diversity and inbreeding coefficients were similar in all populations. Substantial gene flow was found both along altitudinal gradients and horizontally within each elevation belt, although greater values were obtained along altitudinal gradients. Gene flow may be responsible for the homogeneous levels of genetic diversity found among populations. Bayesian cluster analyses also suggested that shifts along altitudinal gradients are the most plausible scenario.

Conclusions

Past population shifts associated with glaciations and interglacial periods in temperate mountains may partially explain current distributions of genetic diversity and population structure. In spite of the predominance of gene flow along the altitudinal gradients, local genetic differentiation of one of the lower populations together with the detection of one outlier locus might support the existence of different selection forces at low altitudes.     

Nuclear DNA microsatellites reveal genetic variation but a lack of phylogeographical structure in an endangered species, Fraxinus mandshurica, across North-east China

Background and Aims

The widely accepted paradigm that the modern genetic structure of plant species in the northern hemisphere has been largely determined by recolonization from refugia after the last glacial maximum fails to explain the presence of cold-tolerant species at intermediate latitudes. Another generally accepted paradigm is that mountain ridges act as important barriers causing genetic isolation of species, but this too has been challenged in recent studies. The aims of the work reported here were to determine the genetic diversity and distribution patterns of extant natural populations of an endangered cool temperate species, Faxinus mandshurica, and to examine whether these two paradigms are appropriate when applied to this species over a wide geographical scale.

Methods

1435 adult individuals were sampled from 30 natural populations across the main and central range of the species, covering major mountain ranges across North-east China (NEC). Genetic variation was estimated based on nine polymorphic nuclear microsatellite loci. Phylogeographical analyses were employed using various approaches, including Bayesian clustering, spatial analysis of molecular variance, Monmonier''s algorithm, neighbor-joining trees, principal co-ordinate analysis and isolation by distance.

Key Results

Genetic diversity within populations was relatively high, and no significant recent bottlenecks were detected in any of the populations. A significant negative correlation between intra-population genetic diversity and latitude was identified. In contrast, genetic differentiation among all the populations examined was extremely low and no clear geographic genetic structure was identified, with the exception of one distinct population.

Conclusions

The modern genetic structure in this species can be explained by extensive gene flow, an absence of mountains acting as barriers, and the presence of a wide refuge across NEC rather than multiple small refugia. Intra-population genetic variation along latitudes is probably associated with the systematically northward shifts of forest biomes in eastern China during the mid-Holocene. To determine important genetic patterns and identify resources for conservation, however, it will be necessary to examine differentially inherited genetic markers exposed to selection pressures (e.g. chloroplast DNA) and to investigate different generations.Key words: Fraxinus mandshurica, nuclear microsatellites, latitude variation, historical migration, fossil pollen, spatial genetic structure, genetic barriers     

Patterns of Genetic Diversity in Rare and Common Orchids Focusing on the Korean Peninsula: Implications for Conservation

To provide basic information for orchid conservation, we surveyed the plant allozyme literature to summarize genetic diversity and structure data for (i) rare orchids native to the Korean Peninsula, and (ii) their congeners irrespective of being common and rare or Korean or not. A total of 68 taxa (32 taxa in Korea and 37 outside Korea; Goodyera repens being included in both datasets) were considered in this study. Overall, rare Korean orchid species had significantly lower levels of genetic diversity than their common congeners and common orchids in general at both population and species levels. However, mean values of G _ST (or F _ST) for rare and common orchids (Korean or not) did not differ significantly from each other. We found patterns of both low and high genetic diversity in rare Korean orchids. Many rare orchids harbored a complete lack of allozyme variation or extremely low within-population variation, perhaps due to rarity associated with random genetic drift and/or, for the case of warm-temperate orchids, to founder effects during post-glacial re-colonization. In contrast, high levels of genetic variation were found for a few orchids that have become recently rare (due to over-collection during the past several decades), probably because there have not been sufficient generations for the initial diversity to be substantially eroded. In addition, several orchids occurring in the main mountain system of the Korean Peninsula (the Baekdudaegan), that served as a glacial refugium, maintained moderate to high levels of within-population genetic diversity. Based on our genetic data, conservation priority should be given to rare orchid species. Particularly, urgent measures should be implemented on Jeju Island, a popular vacation spot, because it also a hotspot for threatened orchids with low levels of genetic diversity.