Density related plasticity in stand-level spatial distribution of the ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae)

We tested the hypothesis that the population density of ambrosia beetles at the stand level influences the spatial distribution of infested trees. We evaluated the spatial distribution of the ambrosia beetle, Platypus koryoensis (Murayama) in three oak forest stands that varied in beetle population density using a multi-year trapping survey. We used these data to inform a clustering analysis based on aggregation indices using the SADIE software. Four important findings emerged: (1) the spatial distribution pattern of P. koryoensis at the stand level changed as the population density of the beetle varied; (2) at low population densities, beetle distribution was contagious at the stand level; (3) as beetle population densities increased, the spatial distribution of infested trees became random, potentially due to beetle avoidance of mass attacked trees; and (4) at high beetle population densities, the spatial distribution of infested trees became contagious, possibly due to temporal changes in location of the attack epicenter within the stand. Our results support the hypothesis that beetle population density has consequences for the spatial distribution of infested trees at the within-stand scale. We conclude that the spatial distribution of infested trees is flexible in response to beetle population density, suggesting that beetle attack behaviors are mediated by one or more density-dependent effects.     

The density distribution of gene loci over the genetic map ofEscherichia coli: Its structural,functional and evolutionary implications

Summary A quantitative analysis was carried out on the dispersion of gene loci over theE. coli genetic map. Therefore, the map was divided into regions characterized by an homogeneous gene density. This created a distribution pattern of gene loci that contained a symmetry axis located near to the origin of DNA replication. The pattern could be subdivided into a set of 22 functional domains containing gene loci whose products revealed a biochemical or functional relatedness. A correlation was found between the boundary positions of these domains and the distribution of F plasmid- and DNA insertion sites over theE. coli chromosome. The structural, functional and evolutionary implications of these findings are discussed.     

Persistence of Dispersal-limited Species in Structured Dynamic Landscapes

Dynamic landscape models have generally assumed random distributions of habitat although real landscapes show spatial organization at many scales. To explore the role of spatial structure in determining the frequency of dispersal-limited forest species, we used a cellular landscape model divided into two zones. Zones were distributed in a random, clustered, or regular spatial pattern. Within each zone habitat cells were randomly destroyed and regenerated, and habitat density and turnover rate were systematically varied. A hypothetical habitat-limited species dispersed between adjacent habitat cells. All trials showed a reduced species frequency relative to a static landscape. Reduction was greater at low habitat density (P = 0.30) than at high density (0.90) suggesting the importance of habitat connectivity in controlling species frequency. The greatest reduction occurred when habitat was concentrated in a small, regularly distributed zone at low habitat density reflecting the enforced isolation of individual habitat cells. Very little reduction was observed when habitat cells were packed into a small clustered zone, a situation promoting connectivity between cells. Moderate–severe frequency reduction occurred when habitat turnover was concentrated in a clustered zone at high habitat density, but little was observed when turnover was widely distributed in a regular or random pattern. These results can be interpreted in terms of a source-sink function in which spatial pattern controlled the degree of contact between landscape zones and determined opportunities for dispersal between habitat cells. We conclude that clustering of forest habitat has the potential to maintain herb species frequency in sparsely forested landscapes. Conversely, clustering of forest disturbance in heavily forested regions, or regular distribution of forest stands (as often occurs in agricultural regions) creates areas which are difficult to colonize, and should be avoided.     

Meiotic Recombination, Noncoding DNA and Genomic Organization in Caenorhabditis Elegans

The genetic map of each Caenorhabditis elegans chromosome has a central gene cluster (less pronounced on the X chromosome) that contains most of the mutationally defined genes. Many linkage group termini also have clusters, though involving fewer loci. We examine the factors shaping the genetic map by analyzing the rate of recombination and gene density across the genome using the positions of cloned genes and random cDNA clones from the physical map. Each chromosome has a central gene-dense region (more diffuse on the X) with discrete boundaries, flanked by gene-poor regions. Only autosomes have reduced rates of recombination in these gene-dense regions. Cluster boundaries appear discrete also by recombination rate, and the boundaries defined by recombination rate and gene density mostly, but not always, coincide. Terminal clusters have greater gene densities than the adjoining arm but similar recombination rates. Thus, unlike in other species, most exchange in C. elegans occurs in gene-poor regions. The recombination rate across each cluster is constant and similar; and cluster size and gene number per chromosome are independent of the physical size of chromosomes. We propose a model of how this genome organization arose.     

Frequent recombination is observed in the distal end of the long arm of chromosome 14

We have constructed a high-resolution map of the distal region (q32) of the long arm of human chromosome 14, with 11 loci including 6 variable number of tandem repeat markers. The map covers 66 cM in males and 53 cM in females. The recombination frequency in this region is more than five times that expected in a region of this physical size, and in our data set the frequency in males was higher than that in females at some intervals. This unusually high density of crossingover occurs in a part of chromosome 14 where translocations are frequently observed in somatic cells.     

Geometrical properties of simulated maize root systems: consequences for length density and intersection density

The spatial distribution of root length density (RLD) is important because it affects water and nutrient uptake. It is difficult to obtain reliable estimates of RLD because root systems are very variable and heterogeneous. We identified systematic trends, clustering, and anisotropy as geometrical properties of root systems, and studied their consequences for the sampling and observation of roots. We determined the degree of clustering by comparing the coefficient of variation of a simulated root system with that of a Boolean model. We also present an alternative theoretical derivation of the relation between RLD and root intersection density (RID) based on the theory of random processes of fibres. We show how systematic trends, clustering and anisotropy affect the theoretical relation between RLD and RID, and the consequences this has for measurement of RID in the field. We simulated the root systems of one hundred maize crops grown for a thermal time of 600 K d, and analysed the distribution of RLD and root intersection density RID on regular grids of locations throughout the simulated root systems. Systematic trends were most important in the surface layers, decreasing with depth. Clustering and anisotropy both increased with depth. Roots at depth had a bimodal distribution of root orientation, causing changes in the ratio of RLD/RID. The close proximity of the emerging lateral roots and the parent axis caused clustering which increased the coefficient of variation.     

Identification of the enzymatic reactions encoded by the purG and purI genes of Escherichia coli

The chromosomal locations of the genes purG and purI on the Escherichia coli linkage map are the opposites of those of Salmonella typhimurium. By methods which permit the identification of lesions in any of the five early enzymes of the purine de novo pathway, the gene-enzyme relationships of the purG and purI loci have been reevaluated in these two organisms. The results demonstrate that the relative locations of the genes encoding the two enzymes (phosphoribosylformylglycinamidine synthetase and phosphoribosylaminoimidazole synthetase) are similar in the two organisms. The gene products have been correctly determined in S. typhimurium. The gene products currently listed for the loci in E. coli are incorrect. The E. coli purG locus is equivalent to the S. typhimurium purI locus, and the E. coli purI locus is equivalent to the S. typhimurium purG locus.     

A linkage map for sugi (Cryptomeria japonica) based on RFLP,RAPD, and isozyme loci

A linkage map for sugi was constructed on the basis of restriction fragment length polymorphism (RFLP), random amplified polymorphic DNA (RAPD), and isozyme loci using a three-generation pedigree prepared for genetic analysis of heartwood color. A total of 128 RFLP (123 cDNA and 5 genomic probes), 33 RAPD, 2 isozyme, and 1 morphological (dwarf) loci segregated in 73 progeny. Of the 164 segregating loci, 145 loci were distributed in 20 linkage groups. Of these loci, 91 with confirmed map positions were assigned to 13 linkage groups, covering a total of 887.3 cM. A clustering of markers with distorted segregation was observed in 6 linkage groups. In the four clusters, distortions with a reduction in the number of homozygotes from one parent only were found.Abbreviations MAS marker-assisted selection - PAGE polyacrylamide gel electrophoresis - QTL quantitative traits of loci - RAPD random amplified polymorphic DNA - RFLP restriction fragment length polymorphism This work was supported by a Grant-in-Aid from the Ministry of Agriculture, Forestry and Fisheries of Japan (Integrated Research Program for the Use of Biotechnological Procedures for Plant Breeding) and by a Grant-in-Aid from the Ministry of Education, Science and Culture of Japan (Cooperative Research, no. 04304017)     

A high-resolution map of Arabidopsis recombinant inbred lines by whole-genome exon array hybridization

Recombinant populations were the basis for Mendel's first genetic experiments and continue to be key to the study of genes, heredity, and genetic variation today. Genotyping several hundred thousand loci in a single assay by hybridizing genomic DNA to oligonucleotide arrays provides a powerful technique to improve precision linkage mapping. The genotypes of two accessions of Arabidopsis were compared by using a 400,000 feature exon-specific oligonucleotide array. Around 16,000 single feature polymorphisms (SFPs) were detected in ~8,000 of the ~26,000 genes represented on the array. Allelic variation at these loci was measured in a recombinant inbred line population, which defined the location of 815 recombination breakpoints. The genetic linkage map had a total length of 422.5 cM, with 676 informative SFP markers representing intervals of ~0.6 cM. One hundred fifteen single gene intervals were identified. Recombination rate, SFP distribution, and segregation in this population are not uniform. Many genomic regions show a clustering of recombination events including significant hot spots. The precise haplotype structure of the recombinant population was defined with unprecedented accuracy and resolution. The resulting linkage map allows further refinement of the hundreds of quantitative trait loci identified in this well-studied population. Highly variable recombination rates along each chromosome and extensive segregation distortion were observed in the population.     

Antibiotic Resistance Mutations in the Chloroplast 16s and 23s Rrna Genes of Chlamydomonas Reinhardtii: Correlation of Genetic and Physical Maps of the Chloroplast Genome

Mutants resistant to streptomycin, spectinomycin, neamine/kanamycin and erythromycin define eight genetic loci in a linear linkage group corresponding to about 21 kb of the circular chloroplast genome of Chlamydomonas reinhardtii. With one exception, all of these mutants represent single base-pair changes in conserved regions of the genes encoding the 16S and 23S chloroplast ribosomal RNAs. Streptomycin resistance can result from changes at the bases equivalent to Escherichia coli 13, 523, and 912-915 in the 16S gene, or from mutations in the rps12 gene encoding chloroplast ribosomal protein S12. In the 912-915 region of the 16S gene, three mutations were identified that resulted in different levels of streptomycin resistance in vitro. Although the three regions of the 16S rRNA mutable to streptomycin resistance are widely separated in the primary sequence, studies by other laboratories of RNA secondary structure and protein cross-linking suggest that all three regions are involved in a common ribosomal neighborhood that interacts with ribosomal proteins S4, S5 and S12. Three different changes within a conserved region of the 16S gene, equivalent to E. coli bases 1191-1193, confer varying levels of spectinomycin resistance, while resistance to neamine and kanamycin results from mutations in the 16S gene at bases equivalent to E. coli 1408 and 1409. Five mutations in two genetically distinct erythromycin resistance loci map in the 23S rDNA of C. reinhardtii, at positions equivalent to E. coli 2057-2058 and 2611, corresponding to the rib3 and rib2 loci of yeast mitochondria respectively. Although all five mutants are highly resistant to erythromycin, they differ in levels of cross-resistance to lincomycin and clindamycin. The order and spacing of all these mutations in the physical map are entirely consistent with our genetic map of the same loci and thereby validate the zygote clone method of analysis used to generate this map. These results are discussed in comparison with other published maps of chloroplast genes based on analysis by different methods using many of the same mutants.     

Identification of spatial genetic boundaries using a multifractal model in human population genetics

There are two purposes in displaying spatial genetic structure. One is that a visual representation of the variation of the genetic variable should be provided in the contour map. The other is that spatial genetic structure should be reflected by the patterns or the gradients with genetic boundaries in the map. Nevertheless, most conventional interpolation methods, such as Cavalli-Sforza's method in genography, inverse distance-weighted methods, and the Kriging technique, focus only on the first primary purpose because of their arbitrary thresholds marked on the maps. In this paper we present an application of the contour area multifractal model (CAMM) to human population genetics. The method enables the analysis of the geographic distribution of a genetic marker and provides an insight into the spatial and geometric properties of obtained patterns. Furthermore, the CAMM may overcome some of the limitations of other interpolation techniques because no arbitrary thresholds are necessary in the computation of genetic boundaries. The CAMM is built by establishing power law relationships between the area A (> or =rho) in the contour map and the value p itself after plotting these values on a log-log graph. A series of straight-line segments can be fitted to the points on the log-log graph, each representing a power law relationship between the area A (> or =rho) and the cutoff genetic variable value for rho in a particular range. These straight-line segments can yield a group of cutoff values, which can be identified as the genetic boundaries that can classify the map of genetic variable into discrete genetic zones. These genetic zones usually correspond to spatial genetic structure on the landscape. To provide a better understanding of the interest in the CAMM approach, we analyze the spatial genetic structures of three loci (ABO, HLA-A, and TPOX) in China using the CAMM. Each synthetic principal component (SPC) contour map of the three loci is created by using both Han and minority groups data together. These contour maps all present an obvious geographic diversity, which gradually increases from north to south, and show that the genetic differences among populations in different districts of the same nationality are greater than those among different nationalities of the same district. It is surprising to find that both the value of p and the fractal dimension alpha have a clear north to south gradient for each locus, and the same clear boundary between southern and northern Asians in each contour map is still seen in the zone of the Yangtze River, although substantial population migrations have occurred because of war or famine in the last 2,000 or 3,000 years. A clear genetic boundary between Europeans and Asians in each contour map is still seen in northwestern China with a small value of alpha, although the genetic gradient caused by gene flow between Europeans and Asians has tended to show expansion from northwestern China. From the three contour maps another interesting result can be found: The values of alpha north of the Yangtze River are generally less than those south of the Yangtze River. This indicates that the genetic differences among the populations north of the Yangtze River are generally smaller than those in populations south of the Yangtze River.     

Identification and characterization of recD, a gene affecting plasmid maintenance and recombination in Escherichia coli.

We isolated mutations that reduce plasmid stability in dividing cell populations and mapped these mutations to a previously undescribed gene, recD, that affects recombination frequency and consequently the formation of plasmid concatemers. Insertions of the transposable element Tn10 into recD resulted in increased concatemerization and loss of pSC101 and ColE1-like replicons during nonselective growth. Both concatemer formation and plasmid instability in recD mutants require a functional recA gene. Mutations in recD are recessive to recD+ and map to a small region of the Escherichia coli chromosome located between recB and argA. Although the recD locus is distinct from loci encoding the two previously identified subunits of the RecBC enzyme, mutations in recD appear to affect the exonuclease activity of this enzyme.     

Genetic analysis of Escherichia coli O111:B4, a strain of medical and biochemical interest.

Procedures have been worked out which allow, for the first time, the genetic analysis of Escherichia coli O111:K58:H2 (O111:B4). The approximate map position of mutant loci was determined by mating with 15 Hfr strains of E. coli K-12. In addition, P1 transduction procedures were used for establishing relative gene order and linkage for any region of the E. coli O111:B4 chromosome. To obtain these, it was necessary to select for a rare P1 lysogen since E. coli O111:B4 is resistant to phage P1. Finally, genetic homology between E. coli strains K-12 and O111:B4 is suggested since they can form stable haploid hybrids, and several loci have similar map positions in the two strains.     

恩施烟区无翅桃蚜在烤烟田空间动态的地统计学分析

恩施烟区是湖北省最大烟叶生产基地,桃蚜Myzuspercicae(Sulzer)是恩施烟叶最重要的害虫之一,桃蚜在田间的发生以及传播的病毒病害逐年加重,给烟业生产带来巨大损失。进一步了解桃蚜发生动态和空间分布规律,将提高对桃蚜的预测效果并为其综合防治提供理论依据。烟区和烟田之间的迁移以有翅蚜为主,田块内部的种群动态和发生规律,无翅桃蚜发挥着更加重要的作用。受寄主生理生化特性影响,不同烟叶生育期,桃蚜空间结构的差异需要进一步验证。经典的统计学方法以纯随机变量为基础,而昆虫种群的田间分布存在空间相关性,地学统计学承认空间相关性的存在,为区域化变量的空间分布分析提供新的理论和方法。在烟叶不同生育期进行无翅桃蚜的田间密度调查,运用地统计学的方法分析了其空间特征和发生动态,模拟了无翅桃蚜在烟叶不同生育期的田间分布图,并对无翅桃蚜在不同烟叶生育期田间分布格局的相关性进行了分析。结果表明:无翅桃蚜在烟叶苗期密度最小为(5.59±4.07)头/株,烟叶旺长期虫口密度最大为(14.5±9.6)头/株;种群密度变异系数均较大(0.6147-0.7281),表明其空间分布的不均匀性,并随密度的增大而减小,表明种群密度的增大一定程度上提高了种群结构的稳定性。烟叶苗期的种群分布曲线峰度最大,表现出更高的聚集性。无翅桃蚜在烟叶苗期的135°方向和团棵期的45。方向表现为随机分布。烟叶苗期的0°方向和45°方向可用线性有基台模型拟合,其他均可用球形+指数套合模型拟合,判断球形+指数套合模型是无翅桃蚜田间分布的主要模型,属于聚集型分布的范畴。块金值、基台值和变程均随田间虫口密度的增大而增大,苗期的随机程度(0.1905—0.7186)明显大于其他时期(0.0116—0.1620)。无翅桃蚜空间分布模拟图可以清晰地看出无翅桃蚜苗期迁移,旺长期后逐渐稳定的特性。无翅桃蚜的田间分布在烟叶苗期与团棵期无明显相关性,而团棵期与旺长期以及旺长期与成熟期显著相关,再次证明烟叶苗期到团棵期,无翅桃蚜的田间分布发生较大迁移,而团棵期以后基本定殖。烟叶苗期的无翅桃蚜高度聚集在少数烟株上,及早预防可以减少烟叶苗期虫口基数,有利于桃蚜种群数量的控制。首次将平面坐标系划分为4个方向,更加准确、全面地描述昆虫种群的空间分布特征。     

The clustering of CpG islands may constitute an important determinant of the 3D organization of interphase chromosomes

We used the 4C-Seq technique to characterize the genome-wide patterns of spatial contacts of several CpG islands located on chromosome 14 in cultured chicken lymphoid and erythroid cells. We observed a clear tendency for the spatial clustering of CpG islands present on the same and different chromosomes, regardless of the presence or absence of promoters within these CpG islands. Accordingly, we observed preferential spatial contacts between Sp1 binding motifs and other GC-rich genomic elements, including the DNA sequence motifs capable of forming G-quadruplexes. However, an anchor placed in a gene/CpG island-poor area formed spatial contacts with other gene/CpG island-poor areas on chromosome 14 and other chromosomes. These results corroborate the two-compartment model of the spatial organization of interphase chromosomes and suggest that the clustering of CpG islands constitutes an important determinant of the 3D organization of the eukaryotic genome in the cell nucleus. Using the ChIP-Seq technique, we mapped the genome-wide CTCF deposition sites in the chicken lymphoid and erythroid cells that were used for the 4C analysis. We observed a good correlation between the density of CTCF deposition sites and the level of 4C signals for the anchors located in CpG islands but not for an anchor located in a gene desert. It is thus possible that CTCF contributes to the clustering of CpG islands observed in our experiments.     

Detection of Nonrandom Association of Alleles from the Distribution of the Number of Heterozygous Loci in a Sample

The distribution of the number of heterozygous loci in two randomly chosen gametes or in a random diploid zygote provides information regarding the nonrandom association of alleles among different genetic loci. Two alternative statistics may be employed for detection of nonrandom association of genes of different loci when observations are made on these distributions: observed variance of the number of heterozygous loci (s2k) and a goodness-of-fit criterion (X2) to contrast the observed distribution with that expected under the hypothesis of random association of genes. It is shown, by simulation, that s2k is statistically more efficient than X2 to detect a given extent of nonrandom association. Asymptotic normality of s2k is justified, and X2 is shown to follow a chi-square (chi 2) distribution with partial loss of degrees of freedom arising because of estimation of parameters from the marginal gene frequency data. Whenever direct evaluations of linkage disequilibrium values are possible, tests based on maximum likelihood estimators of linkage disequilibria require a smaller sample size (number of zygotes or gametes) to detect a given level of nonrandom association in comparison with that required if such tests are conducted on the basis of s2k. Summarization of multilocus genotype (or haplotype) data, into the different number of heterozygous loci classes, thus, amounts to appreciable loss of information.     

The clustering of CpG islands may constitute an important determinant of the 3D organization of interphase chromosomes

We used the 4C-Seq technique to characterize the genome-wide patterns of spatial contacts of several CpG islands located on chromosome 14 in cultured chicken lymphoid and erythroid cells. We observed a clear tendency for the spatial clustering of CpG islands present on the same and different chromosomes, regardless of the presence or absence of promoters within these CpG islands. Accordingly, we observed preferential spatial contacts between Sp1 binding motifs and other GC-rich genomic elements, including the DNA sequence motifs capable of forming G-quadruplexes. However, an anchor placed in a gene/CpG island-poor area formed spatial contacts with other gene/CpG island-poor areas on chromosome 14 and other chromosomes. These results corroborate the two-compartment model of the spatial organization of interphase chromosomes and suggest that the clustering of CpG islands constitutes an important determinant of the 3D organization of the eukaryotic genome in the cell nucleus. Using the ChIP-Seq technique, we mapped the genome-wide CTCF deposition sites in the chicken lymphoid and erythroid cells that were used for the 4C analysis. We observed a good correlation between the density of CTCF deposition sites and the level of 4C signals for the anchors located in CpG islands but not for an anchor located in a gene desert. It is thus possible that CTCF contributes to the clustering of CpG islands observed in our experiments.     

Identification, characterization, and mapping of the Escherichia coli htrA gene, whose product is essential for bacterial growth only at elevated temperatures.

We identified and cloned an Escherichia coli gene called htrA (high temperature requirement). The htrA gene was originally discovered because mini-Tn10 transposon insertions in it allowed E. coli growth at 30 degrees C but prevented growth at elevated temperatures (above 42 degrees C). The htrA insertion mutants underwent a block in macromolecular synthesis and eventually lysed at the nonpermissive temperature. The htrA gene was located at approximately 3.7 min (between the fhuA and dapD loci) on the genetic map of E. coli and between 180 and 187.5 kilobases on the physical map. It coded for an unstable, 51-kilodalton protein which was processed by removal of an amino-terminal fragment, resulting in a stable, 48-kilodalton protein.     

Comparison of homoeologous group-6 short arm physical maps of wheat and barley reveals a similar distribution of recombinogenic and gene-rich regions

Eighty two new loci, mapped with 51 DNA clones, were added to the earlier deletion maps of the homoeologous group-6 short arms of hexaploid wheat ( Triticum aestivum L. em Thell., 2n = 6 x = 42, AABBDD). There are now 41, 56 and 52 loci mapped on deletion maps of 6AS, 6BS and 6DS, respectively. The linear order of orthologous loci in all three arms appears to be identical. The majority of the loci are located in the distal one-half of the three arms. There seems to be an increased marker/gene density from the centromeric to the telomeric regions in each arm, and the marker density in comparable physical regions is similar on all three maps. Recombination is not uniformly distributed along the chromosome arms; 60% of recombination occurs in the distal one-third of each arm. Recombination increases from the proximal region to the distal end in a nonlinear pattern. The distribution of loci and recombination along each of the three chromosome arms is highly correlated. Comparison of the 6BS deletion map from this study and a 6HS physical map of barley ( Hordeum vulgare L., 2n = 2 x = 14, HH) reveals a remarkably similar distribution of recombinogenic and gene-rich regions between the two chromosome arms, suggesting that the distribution patterns of genes may be conserved in the homoeologous group-6 chromosome short arms of wheat and barley. A consensus map of wheat group-6 short arms containing 46 orthologous loci was constructed. Comparison of the consensus map with published linkage maps of Triticeae group-6 chromosome short arms indicates that the linear order of the loci on the maps has been largely conserved. Evidence from this study does not support the existence of a 2BS-6BS reciprocal terminal translocation.