Genetic differentiation of Arthrobacter population from heavy metal-contaminated environment

Six samples containing extremely high concentration of Pb, Zn, and Cd were obtained from the layers of 5–10 cm and 25–30 cm three tailing piles, with ages of about 10, 20 and more than 80 years, respectively. Then, 48 bacterial strains were obtained from these samples, and subsequently their phylogenetic positions were determined by analysis on the partial sequence of 16S rRNA gene (fragment length ranging from 474 to 708 bp). These isolates were members of the Arthrobacter genus, phylogenetically close to A. keyseri and A. ureafaciens, with sequence ranging from 99.1% to 100%. Furthermore, genetic variation between subpopulations from different samples was revealed by analysis on their randomly amplified polymorphic DNA profile. Nei genetic distance showed that the greatest differentiation occurred between subpopulation A and C. Notably, either genetic distance between subpopulations from the layers of 5–10 cm and 25–30 cm of each tailing pile or between same layers of different tailing pile increased with the history of tailings. Moreover, correlation analysis showed that soluble Pb has a significantly negative relationship with Nei’ gene diversity of subpopulation. It was assumed that soluble Pb may be responsible for the reduced genetic diversity of the Arthrobacter population. Our data provided evidence that genetic differentiation of microbial populations was consistent with the changes of environmental factors, particularly heavy metals. Translated from Acta Ecologica Sinica, 2005, 25(10): 2569–2573 [译自: 生态学报]     

Microsatellite diversity, population subdivision and gene flow in the Lipizzan horse

Blood samples of 561 Lipizzan horses from subpopulations (studs) of seven European countries representing a large fraction of the breed's population were used to examine the genetic diversity, population subdivision and gene flow in the breed. DNA analysis based on 18 microsatellite loci revealed that genetic diversity (observed heterozygosity = 0.663, gene diversity = 0.675 and the mean number of alleles = 7.056) in the Lipizzan horse is similar to other horse breeds as well as to other domestic animal species. The genetic differentiation between Lipizzan horses from different studs, although moderate, was apparent (pairwise F(ST) coefficients ranged from 0.021 to 0.080). Complementary findings explaining the genetic relationship among studs were revealed by genetic distance and principal component analysis. One genetic cluster consisted of the subpopulations of Austria, Italy and Slovenia, which represent the classical pool of Lipizzan horse breeding. A second cluster was formed by the Croatian, Hungarian and Slovakian subpopulations. The Romanian subpopulation formed a separate unit. The largest genetic differentiation was found between the Romanian and Italian subpopulation. Genetic results are consistent with the known breeding history of the Lipizzan horse. Correct stud assignment was obtained for 80.9% and 92.1% of Lipizzan horses depending on the inclusion or exclusion of migrant horses, respectively. The results of the present study will be useful for the development of breeding strategies, which consider classical horse breeding as well as recent achievements of population and conservation genetics.     

GENETIC VARIABILITY OF GELIDIUM CANARIENSIS (RHODOPHYTA) DETERMINED BY ISOZYME ELECTROPHORESIS1

The populations of Gelidium canariensis (Grunow) Seoane-Camba from the Canary Islands were analyzed for genetic variability by isozyme electrophoresis in 1989 and 1990. Each population was divided into sporophytic and gametophytic subpopulations. Twenty-three to 27 putative alleles corresponding to 22 gene loci were analyzed. Sev-enteen loci were monomorphic in all six subpopulations, and five were polymorphic in at least one subpopulation. Significant deviations from Hardy-Weinberg equilibrium were found. The amount of genetic variability (percentage of polymorphic loci, mean number of alleles per locus, and average gene diversity) of haploid subpopulations was lower than that of diploid subpopulations. No correlation between genetic distance and geographical distance was found. Low genetic differentiation between sporophytic and gametophytic subpopulations of the same locality was obsewed in two populations. The low genetic diversity and genetic differentiation suggest that the genetic structure of the populations of G. canariensis from the Canary Islands is due to a combination of founder effects and the predominance of asexual reproduction. Initial differences in gene frequencies may have persisted because of insufficient time to reach a higher level of differentiation.     

Among- and within-patch components of genetic diversity respond at different rates to habitat fragmentation: an empirical demonstration

Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulation, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulation and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetics data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in population of an alpine meadow-dwelling butterfly, which have become fragmented increasing forest cover over five decades. We show that genetic differentiation among subpopulations (G(ST)) is most highly correlated with contemporary forest cover, while genetics diversity within subpopulation (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulation can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.     

Genetic variation,population structure and identification of yellow catfish, <Emphasis Type="Italic">Mystus nemurus</Emphasis> (C&;V) in Thailand using RAPD,ISSR and SCAR marker

Random amplified polymorphic DNA (RAPD) and inter-simple sequence repeat (ISSR) markers were used to investigate the genetic structure of four subpopulations of Mystus nemurus in Thailand. The 7 RAPD and 7 ISSR primers were selected. Of 83 total RAPD fragments, 80 (96.39%) were polymorphic loci, and of 81 total ISSR fragments, 75 (92.59%) were polymorphic loci. Genetic variation and genetic differentiation obtained from RAPD fragments or ISSR fragments showed similar results. Percentage of polymorphic loci (%P), observed number of alleles, effective number of alleles, Nei’s gene diversity (H) and Shannon’s information index revealed moderate to high level of genetic variations within each M. nemurus subpopulation and overall population. High levels of genetic differentiations were received from pairwise unbiased genetic distance (D) and coefficient of differentiation. Mantel test between D or gene flow and geographical distance showed a low to moderate correlation. Analysis of molecular variance indicated that variations among subpopulations were higher than those within subpopulations. The UPGMA dendrograms, based on RAPD and ISSR, showing the genetic relationship among subpopulations are grouped into three clusters; Songkhla (SK) subpopulation was separated from the other subpopulations. The candidate species-specific and subpopulation-specific RAPD fragments were sequenced and used to design sequence-characterized amplified region primers which distinguished M. nemurus from other species and divided SK subpopulation from the other subpopulations. The markers used in this study should be useful for breeding programs and future aquacultural development of this species in Thailand.     

Genome-wide SNP typing reveals signatures of population history

Single-nucleotide polymorphism (SNP) arrays have become a popular technology for disease-association studies, but they also have potential for studying the genetic differentiation of human populations. Application of the Affymetrix GeneChip Human Mapping 500K Array Set to a population of 102 individuals representing the major ethnic groups in the United States (African, Asian, European, and Hispanic) revealed patterns of gene diversity and genetic distance that reflected population history. We analyzed allelic frequencies at 388,654 autosomal SNP sites that showed some variation in our study population and 10% or fewer missing values. Despite the small size (23-31 individuals) of each subpopulation, there were no fixed differences at any site between any two subpopulations. As expected from the African origin of modern humans, greater gene diversity was seen in Africans than in either Asians or Europeans, and the genetic distance between the Asian and the European populations was significantly lower than that between either of these two populations and Africans. Principal components analysis applied to a correlation matrix among individuals was able to separate completely the major continental groups of humans (Africans, Asians, and Europeans), while Hispanics overlapped all three of these groups. Genes containing two or more markers with extraordinarily high genetic distance between subpopulations were identified as candidate genes for health differences between subpopulations. The results show that, even with modest sample sizes, genome-wide SNP genotyping technologies have great promise for capturing signatures of gene frequency difference between human subpopulations, with applications in areas as diverse as forensics and the study of ethnic health disparities.     

Genetic Variation and Differentiation of Larix decidua Populations in Swiss Alps (in English)

Genetic diversity within and among six subpopulations of Larix decidua Mill. from two altitudinal transects of Swiss Alps was investigated using 6 enzyme systems coding for 8 loci. Globally, the mean proportion of polymorphic loci was 22.9%, the average number of alleles per locus was 1.3, and the mean expected heterozygosity was 0.095. Only 5.8% of the genetic variation resided among populations. The mean genetic distance was 0.006. Several significant differences of gene frequencies were found between different age classes. Positive values of the species mean fixation index observed in this study suggested a considerable deficit of heterozygotes in the populations of L. decidua of Swiss Alps. At one of the sites (Arpette), the highest subpopulation in elevation gave the lowest level of genetic diversity (as evidenced by the lowest proportion of polymorphic loci and the lowest mean expected heterozygosity) and the largest value of genetic distance when compared to other subpopulations. The genetic differences between the highest subpopulation and the other ones suggest that the founder effect may be an important factor influencing genetic differentiation of L. decidua populations at Arpette transect.     

瑞士阿尔卑斯山欧洲落叶松居群的遗传变异和分化

应用等位酶分析技术,沿两个海拔梯度在瑞士阿尔卑斯山研究了欧洲落叶松（Larix decidua Mill.)居群内和居群间的遗传多态性,结果表明,多态性位点的比例为22.9%,平均每个位点的等位基因数为1.3,平均期望杂合度为0.095,遗传变异的5.8%存在于居群之间,平均遗传距离为0.006。几个有统计意义的基因频率差别在不同树龄类被发现,正在繁育系数值表明在瑞士阿尔卑斯山欧洲落叶松居群有相当的杂合体缺乏,在阿尔拜特（Ar-pette),海拔最高的亚居群与其他亚居群相比较显示最低的遗传多态性（如显示最低的我态性位点比例和最低的平均期望杂合度）和最大的遗传距离值,在最高亚居群和其他亚居群间的遗传差别暗示奠基效应可能是影响这个定样场所欧洲落叶松居群遗传分化的主要因素。     

Pedigree estimation of the (sub) population contribution to the total gene diversity: the horse coat colour case

A method to quantify the contribution of subpopulations to genetic diversity in the whole population was assessed using pedigree information. The standardization of between- and within-subpopulation mean coancestries was developed to account for the different coat colour subpopulation sizes in the Spanish Purebred (SPB) horse population. The data included 166264 horses registered in the SPB Studbook. Animals born in the past 11 years (1996 to 2006) were selected as the 'reference population' and were grouped according to coat colour into eight subpopulations: grey (64 836 animals), bay (33 633), black (9414), chestnut (1243), buckskin (433), roan (107), isabella (57) and white (37). Contributions to the total genetic diversity were first assessed in the existing subpopulations and later compared with two scenarios with equal subpopulation size, one with the mean population size (13 710) and another with a low population size (100). Ancestor analysis revealed a very similar origin for the different groups, except for six ancestors that were only present in one of the groups likely to be responsible for the corresponding colour. The coancestry matrix showed a close genetic relationship between the bay and chestnut subpopulations. Before adjustment, Nei's minimum distance showed a lack of differentiation among subpopulations (particularly among the black, chestnut and bay subpopulations) except for isabella and white individuals, whereas after adjustment, white, roan and grey individuals appeared less differentiated. Standardization showed that balancing coat colours would contribute preserving the genetic diversity of the breed. The global genetic diversity increased by 12.5% when the subpopulations were size standardized, showing that a progressive increase in minority coats would be profitable for the genetic diversity of this breed. The methodology developed could be useful for the study of the genetic structure of subpopulations with unbalanced sizes and to predict their genetic importance in terms of their contribution to genetic variability.     

Genetic structure and gene flow in a metapopulation of an endangered plant species,Silene tatarica

We investigated the distribution of genetic variation within and between seven subpopulations in a riparian population of Silene tatarica in northern Finland by using amplified fragment length polymorphism (AFLP) markers. A Bayesian approach-based clustering program indicated that the marker data contained not only one panmictic population, but consisted of seven clusters, and that each original sample site seems to consist of a distinct subpopulation. A coalescent-based simulation approach shows recurrent gene flow between subpopulations. Relative high FST values indicated a clear subpopulation differentiation. However, amova analysis and UPGMA-dendrogram did not suggest any hierarchical regional structuring among the subpopulations. There was no correlation between geographical and genetic distances among the subpopulations, nor any correlation between the subpopulation census size and amount of genetic variation. Estimates of gene flow suggested a low level of gene flow between the subpopulations, and the assignment tests proposed a few long-distance bidirectional dispersal events between the subpopulations. No apparent difference was found in within-subpopulation genetic diversity among upper, middle and lower regions along the river. Relative high amounts of linkage disequilibrium at subpopulation level indicated recent population bottlenecks or admixture, and at metapopulation levels a high subpopulation turnover rate. The overall pattern of genetic variation within and between subpopulations also suggested a 'classical' metapopulation structure of the species suggested by the ecological surveys.     

Genetic structure and differentiation of Psathyrostachys huashanica populations detected with RAPD markers

Psathyrostachys huashanica Keng is a perennial grass and belongs to genus Psathyrostachys under Triticeae.sathyrostachys is found in the center of Middle Asia and the Caucasus Mountain,while P.huashanica,a species endemic to China,is only located in Mt.Hua in the Shaanxi province,China.At present,the population of this species is decreasing,and reaching the edge of extinction.Due to the limitation in distribution and the importance as breeding material for germplasm storage,it has been considered as first class among the national protected rare plants.For this reason,the present study is significant in probing plant flora,origin and evolution of Triticeae,and crop breeding.Randomly amplified polymorphic DNA (RAPD)markers were used to analyze the genetic structure and differentiation of P.huashanica populations sampled in three valleys (Huangpu,Xian,and Huashan Valleys)in Mr.Hua.One hundred and twenty-two RAPDfragments were obtained in all 266 individuals with 20 primers with a mean of 6.1 (2-10)fragments per primer.The percentage of polymorphic loci (PPB)was 60.66%in Huangpu Valley,90.98%in Xian Valley,95.08%in Huashan Valley,and the total PPB was 95.08%,which indicated a highly genetic variability of P.huashanica.The Shannon's Information index and GST were 0.3306 and 0.3263,respectively,indicating that there were more genetic variations within the subpopulations than those among the subpopulations.The gene flow among the subpopulations of P.huashanica (Nm=1.0322)was much less than that of the common anemophytes (Nm=5.24).Mean genetic distance is 0.1571(range:0.0022-0.2901).The highest value of genetic distance was found between the subpopulation (hp1)of Huangpu Valley and the highest altitude subpopulation (h8)of Huashan Valley.Correlation analysis detected significant correlation between genetic distance and vertical distance of altitude.Clustering analysis and principal coordinate analysis revealed the genetic differentiation among the populations of P.huashanica.Differentiation mainly occurred between the higher altitude subpopulations and the lower altitude subpopulations,suggesting that altitude might be the major factor that restricted the gene flow between different altitude subpopulations and resulted in differentiation of subpopulations.     

Evaluation of Genetic Diversity and Population Structure Analysis among Germplasm of Agaricus bisporus by SSR Markers

Agaricus bisporus is a popular edible mushroom that is cultivated worldwide. Due to its secondary homothallic nature, cultivated A. bisporus strains have low genetic diversity, and breeding novel strains is challenging. The aim of this study was to investigate the genetic diversity and population structure of globally collected A. bisporus strains using simple sequence repeat (SSR) markers. Agaricus bisporus strains were divided based on genetic distance-based groups and model-based subpopulations. The major allele frequency (MAF), number of genotypes (NG), number of alleles (NA), observed heterozygosity (HO), expected heterozygosity (HE), and polymorphic information content (PIC) were calculated, and genetic distance, population structure, genetic differentiation, and Hardy–Weinberg equilibrium (HWE) were assessed. Strains were divided into two groups by distance-based analysis and into three subpopulations by model-based analysis. Strains in subpopulations POP A and POP B were included in Group I, and strains in subpopulation POP C were included in Group II. Genetic differentiation between strains was 99%. Marker AB-gSSR-1057 in Group II and subpopulation POP C was confirmed to be in HWE. These results will enhance A. bisporus breeding programs and support the protection of genetic resources.     

Large‐scale population genetic structure in Bonelli's Eagle Aquila fasciata

In bird species that have a high movement capacity, dispersal may connect subpopulations over vast geographical regions, with important consequences for the design of conservation management strategies. Here we used a molecular approach to infer the patterns and rates of dispersal among eight Mediterranean subpopulations of the endangered Bonelli's Eagle, based on 245 individuals screened at 17 microsatellite loci. There was moderate genetic differentiation between subpopulations sampled in the western (Iberia and Morocco) and eastern (Cyprus) Mediterranean, whereas differentiation among subpopulations in the former region was weak to moderate and followed a pattern of isolation by distance. Within the western Mediterranean, the small, peripheral and ecologically unique population of southwest Portugal had the lowest genetic diversity and the highest differentiation. The remaining subpopulations formed two loose clusters, one including Morocco and southwest and eastern Spain, and the other northeast Portugal and western and central Spain. Few recent migrants were detected, and they originated primarily from adjacent subpopulations. Our findings suggest that western Mediterranean Bonelli's Eagles may have a large‐scale metapopulation structure, with subpopulations connected to some extent by distance‐dependent dispersal, probably influenced by natal philopatry and the geographical configuration of subpopulations. The combination of marked ecological and genetic divergence suggests that the peripheral subpopulation of southwest Portugal may be regarded as a distinct management unit.     

THE RELEVANCE OF GENE FLOW IN METAPOPULATION DYNAMICS OF AN OCEANIC ISLAND ENDEMIC,OLEA EUROPAEA SUBSP. GUANCHICA

Theoretical and empirical studies suggest that geographical isolation and extinction–recolonization dynamics are two factors causing strong genetic structure in metapopulations, but their consequences in species with high dispersal abilities have not been tested at large scales. Here, we investigated the effect of population age structure and isolation by distance in the patterns of genetic diversity in a wind‐pollinated, zoochorous tree (Olea europaea subsp. guanchica) sporadically affected by volcanic events across the Canarian archipelago. Genetic variation was assessed at six nuclear microsatellites (nDNA) and six chloroplast fragments (cpDNA) in nine subpopulations sampled on four oceanic islands. Subpopulations occurring on more recent substrates were more differentiated than those on older substrates, but within‐subpopulation genetic diversity was not significantly different between age groups for any type of marker. Isolation‐by‐distance differentiation was observed for nDNA but not for cpDNA, in agreement with other metapopulation studies. Contrary to the general trend for island systems, between‐island differentiation was extremely low, and lower than differentiation between subpopulations on the same island. The pollen‐to‐seed ratio was close to one, two orders of magnitude lower than the average estimated for other wind‐pollinated, animal‐dispersed plants. Our results showed that population turnover and geographical isolation increased genetic differentiation relative to an island model at equilibrium, but overall genetic structure was unexpectedly weak for a species distributed among islands. This empirical study shows that extensive gene flow, particularly mediated by seeds, can ameliorate population subdivision resulting from extinction–recolonization dynamics and isolation by distance.     

Patterns of Allelic Diversity in Spring Wheat Populations by SSR-Markers

Precise assessment of diversity in available breeding germplasm helps to preempt epidemics and abrupt environmental changes. Spring wheat germplasm consisting of 84 accessions including cultivars, breeding lines and landraces from various origins was scanned with 44 SSRs. For allele frequencies, allelic patterns, heterozygosity and polymorphism the selected population was divided in three subpopulations: (i) pre-green revolution (pre-1965), (ii) post-green revolution (post-1965), (iii) post-veery (post-2000). Alleles produced in pre-1965, post-1965 and post-2000 subpopulations were 115, 144 and 131, respectively. Mean PIC values for pre-1965, post-1965 and post-2000 subpopulations were 0.48, 0.52 and 051, respectively. Allelic patterns showed no locally common alleles in any of the subpopulation. The pre-1965 subpopulation had also no private allele, however, average number of private alleles decreased from post-1965 to post-2000 subpopulation. In case of effective alleles and Shannon’s information index trend was increasing from pre-1965 to post-1965 and then decreasing from post-1965 to post-2000. The decreasing trend alarms the reduced genetic diversity in wheat varieties developed after 2000. PCA and cluster analysis didn’t clearly differentiated subpopulations, though pre-1965 genotypes showed higher genetic distance from post-1965 and post-2000 subpopulations. The decreasing measures of genetic diversity in post-2000 wheat genotypes should be a concern for wheat breeders, therefore, all sources of broadening genetic diversity should be exploited.     

德兴铜矿尾矿重金属污染对土壤中微生物多样性的影响

【目的】为更好地了解重金属污染与微生物多样性之间的相互作用关系,以江西德兴铜矿4#尾砂库为研究对象,采集野外实地样品共16件进行分析(包括尾砂样品以及周围农田和菜地土壤样品)。【方法】一方面对样品中可培养异养细菌进行平板计数,一方面采用变性梯度凝胶电泳(Denaturing gradient gel electrophoresis,DGGE)对样品中可培养和不可培养微生物分子生态多样性进行研究;同时采用PCA(Principle component analysis)方法分析样品理化性质、重金属及主要元素与可培养细菌数量及微生物多样性之间的相互关系。【结果】元素分析结果表明该尾矿区样品受到不同程度重金属Cu、Cd、Zn、Ni、Pb和Cr的污染;可培养异养细菌在尾砂样品中数量最少,在菜地和农田土壤样品中有明显增加;多样性指数(Shannon-Weaver index H)计算结果发现H最大值出现在距离尾矿中等距离、重金属浓度在中等程度的样品中。PCA分析结果表明可培养异养菌数量与理化性质如有机碳、有机质、含水率等相关性较大,重金属影响不明显;而多样性指数H除与上述理化性质相关性较大外,还受到重金属Ag、Zn、As、Pb、Ni、Cr等的影响,而在样品中含量普遍比较高的重金属如Cu、Cd等并不成为影响微生物多样性的主要因素。【结论】从这些长期受重金属污染的野外实地样品来看,以上结果说明不同重金属浓度对微生物多样性的影响可能并不是实验室研究的简单的线性关系。     

Population genetic structure of the tropical tree species Aegiphila sellowiana (Lamiaceae)

The Tibagi River, located in southern Brazil, is associated with a significant degree of environmental heterogeneity, along its 550 km extension. There is concern about the integrity of this river's ecosystem, as human interference has been increasing. Aegiphila sellowiana (Lamiaceae) is an important pioneer tree species, commonly found near rivers; the fruit is consumed by avifauna. We studied this species along three ecological gradients, comprising the upper, middle, and lower regions of the Tibagi River basin. The genetic structure of nine subpopulations of A. sellowiana distributed along these gradients was investigated using RAPDs. Moderate levels of gene diversity (ranging from 0.091 to 0.132) were identified, inferred by a traditional approach and a Bayesian model-based method. The F-statistic, G(ST) parameters and molecular variance analysis showed high genetic differentiation among the three regions (39.5 to 50.26%). Analysis of molecular variance revealed high levels of genetic variation between populations (50.26%), while lower values of genetic variation (ranging from 9.56 to 16.35%) were seen between subpopulations within the upper, middle, and lower regions of the Tibagi River basin. The validity of these results was confirmed by principal coordinate analysis. Linear regression analysis showed significant correlations (r = 0.621, P = 0.0001) between the genetic and geographical distances. The differences observed in genetic variation between regions are probably due to habitat fragmentation; for conservation purposes, we recommend that at least one subpopulation from each region of the Tibagi River should be maintained.     

Correlation between genetic and geographic structure in Europe

Understanding the genetic structure of the European population is important, not only from a historical perspective, but also for the appropriate design and interpretation of genetic epidemiological studies. Previous population genetic analyses with autosomal markers in Europe either had a wide geographic but narrow genomic coverage [1] and [2], or vice versa [3], [4], [5] and [6]. We therefore investigated Affymetrix GeneChip 500K genotype data from 2,514 individuals belonging to 23 different subpopulations, widely spread over Europe. Although we found only a low level of genetic differentiation between subpopulations, the existing differences were characterized by a strong continent-wide correlation between geographic and genetic distance. Furthermore, mean heterozygosity was larger, and mean linkage disequilibrium smaller, in southern as compared to northern Europe. Both parameters clearly showed a clinal distribution that provided evidence for a spatial continuity of genetic diversity in Europe. Our comprehensive genetic data are thus compatible with expectations based upon European population history, including the hypotheses of a south-north expansion and/or a larger effective population size in southern than in northern Europe. By including the widely used CEPH from Utah (CEU) samples into our analysis, we could show that these individuals represent northern and western Europeans reasonably well, thereby confirming their assumed regional ancestry.     

Genetic differentiation in Eurasian populations of the postfire ascomycete Daldinia loculata

The genetic population structure of the postfire ascomycete Daldinia loculata was studied to test for differentiation on a continental scale. Ninety-six samples of spore families, each comprising mycelia from six to 10 spores originating from single perithecia, were sampled from one Russian and six Fennoscandian forest sites. Allelic distribution was assayed for six nuclear gene loci by restriction enzyme analyses of polymerase chain reaction (PCR)-amplified gene fragments. In addition, the full sequence of the gene fragment was analysed for a subset of haploid single-ascospore isolates in a multiallelic approach. A third data set was generated by using arbitrary-primed PCR with the core sequence of the phage M13 as primer. Although there was a reduction in heterozygosity in the total population from what would have been expected at random mating, the levels of genetic differentiation among the Eurasian subpopulations of D. loculata were low. All subpopulations were found to be in Hardy-Weinberg equilibrium and gametic equilibrium was observed between all investigated nuclear gene loci. The results obtained by the different markers were consistent; we confirmed low levels of genetic differentiation among the Eurasian subpopulations of D. loculata. The differentiation did not increase with distance; the Russian subpopulation, sampled more than 7000 km from the Fennoscandian subpopulations, was only moderately differentiated from the others (FST = 0.00-0.14). In contrast, one of the Swedish populations was the most highly differentiated from the others, with FST and GST values of 0.10-0.16. The results suggest that D. loculata consists of a long-lived background Eurasian population of latent mycelia in nonburned forests, established by sexual ascospores dispersed from scattered burned forest sites. Local differentiation is probably due to founder effects of populations in areas with low fire frequency. A tentative life cycle of D. loculata is presented.     

Microsatellite markers reveal genetic diversity of wild soybean in different habitats and implications for conservation strategies (Glycine soja) in China

Wild soybean individuals were sampled from ten habitat sites in Beijing region, China and were assessed using 36 SSR markers for the genetic variation among the habitat subpopulations. AMOVA analysis showed 57.46 % inter-population and 42.54 % intrapopulation genetic variation. The genetic variation had geographical regionality. The drought-stressed and founder subpopulations intensively reduced genetic diversity, and along-river system habitats appeared to have closer genetic similarity. The bottleneck impact of drought stress appeared to be inferior to the founding effect on subpopulation genetic diversity but superior on genetically geographical grouping. Here, all the subpopulations were found to contain unique alleles. The phenotypic and genetic diversities had similarly fluctuated patterns across the subpopulations. These results here suggest that a conservation strategy should be taken: theoretically as many as possible populations are sampled to maximize the genetic diversity in ex situ conservation of wild soybean within an area in China. Spatial distance should be considered for isolating wild soybean populations when genetically modified soybeans are cultivated in China.