Wolves, moose, and the allometry of population cycles

After a decade of dramatic population fluctuations, protected populations of wolves and moose in Isle Royale National Park in Lake Superior returned in 1983 to the levels observed in the 1950's. Inherent lags in this predator-prey system and the strong recovery of the moose population following a wolf population crash suggest that these populations may continue to cycle with a period length of about 38 (95 percent confidence interval, +/-13) years. Such a long-term cycle is consistent with the proposal that period length of herbivore population cycles will characteristically scale according to the fourth root of body mass, a basic allometric relation linking physiological cycles to population processes.     

混合选择与改良S#-1家系选择对玉米群体的改良效果研究

本研究完成了玉米群体中综3号（ZZ-3）C#-0的三轮混合选择和一轮改良S#-1选择。结果表明,两种方法对这个群体均有改良效果。经过三轮混合选择,依照两种不同的选择标准而分成的群体ZZ-3（M#-1）C#-3和ZZ-3（M#-2）C#-3比原始群体分别提高产量12.7%和11.4%,达到1%显著差异水平。经过一轮改良S#-1选择,所选标准有相应区别的群体ZZ-3（S#-1-1）C#-1和ZZ-3（S#-1-2）C#-1产量分别提高了8.5%和10.3%,也达到极显著水平。改良S#-1选择法的一轮选择效果相当于混合选择法的2-3轮。 对中综3号群体所选的目标性状,粒行数以16-20行之间为宜,过分加强粒行数的选择会影响改良群体的效果。 混合选择呈现出逐代累加的选择效果,在上述两种方法中,对产量进行选择,均伴随着穗长、每行粒数、穗粗、百粒重的增长。以粒行数而言,则没有多大变化,这可能是由于基础群体的平均粒行数19.15已达到相当高值的缘故。     

Influence of Host Shift on Genetic Differentiation of the Oriental Fruit Fly,Bactrocera dorsalis

Invasion of the oriental fruit fly, Bactrocera dorsalis, into new niches containing different food sources (a process referred to as host shift), may cause population genetic differentiation and sympatric speciation. To attempt to infer that experimentally, test populations were established by transferring a subset of the original populations, which had been grown on banana for many generations, onto navel orange, and then subculturing the navel orange population and banana population for at least 20 generations. Four pairs of SSR primers with high polymorphism on laboratory strains were used to detect population genetic differentiation. All six tested populations (the 5th, 10th and 15th generations of B. dorsalis fed on banana and navel orange, respectively) were found to have low genetic diversity. Furthermore, the genetic diversity of the navel orange populations was found to decline after being crossed for several generations. Populations initially were deviated from Hardy-Weinberg equilibrium, however, equilibrium was achieved with increasing numbers of generations in both of the host populations. Limited gene flows were found among the six populations. The Nei's standard genetic distances between the two host populations of the same generation were initially low, but increased with generation number. Genetic distances between banana and navel orange populations of the same generation were lower than genetic distances between different generations grown on the same host plant. Analysis of molecular distance (AMOVA) results based on generation groups and host groups demonstrated that genetic variation among generations was greater than that between the two host populations. The results indicated that population genetic differentiation occurred after the host shift, albeit at low level. Biogeography and taxonomy of the B. dorsalis complex revealed that speciation of B. dorsalis might be tightly associated with host shift or host specialization of B. dorsalis following dispersal.     

Genetic Diversity of Recurrent Selection Populations with Ms2 Gene Assessed by Gliadins in Common Wheat （Triticum aestivum L.）

The male-sterile lines with Ms2 gene were highly evaluated in recurrent selection in wheat （Triticum aestivum L.）. Three populations C6 （population after six cycles of selection）, C7 （population after seven cycles of selection）, and C8 （population after eight cycles of selection） were constructed through recurrent selection with 12 parental materials （P）. Acid polyacrymide gel electrophoresis （A-PAGE） analysis was used to identify gliadin patterns and evaluate the genetic diversity in 12 parents and three populations. A total of 63 bands were identified, of which 17 polymorphic bands and 7 unique bands were present in populations and seven polymorphic bands and four unique bands were present in parents. The number of polymorphic and unique bands decreased gradually from C6 to C8, especially for to- and y-gliadins. The genetic distances in C6, C7, and C8 were calculated. The distributions of genetic distance were different in three recurrent selection populations. From C6 to C8, the genetic distance was 0.2687, 0.2652 and 0.1987, respectively. Statistically significant differences were detected between C7 and C8 with the T value of 37.9718. The result of cluster analysis based on genetic similarity matrix of three populations fitted well to those of principle coordinates analysis （PCoA）. Compared with 12 parents, almost all individuals of three populations are new genotypes. Most of the individuals from C6 and C7 could be divided into two groups, while most individuals of C8 were in one cluster. In conclusion, the results indicated that the genetic diversity was decreased severely according to the information revealed by A-PAGE, although some variations could be created in the recurrent selection. It was necessary to introduce diverse germplasm based on the genetic database of recurrent population to maintain and improve the breeding efficiency in the further program.     

Chaos versus noisy periodicity: alternative hypotheses for childhood epidemics

Whereas case rates for some childhood diseases (chickenpox) often vary according to an almost regular annual cycle, the incidence of more efficiently transmitted infections such as measles is more variable. Three hypotheses have been proposed to account for such fluctuations. (i) Irregular dynamics result from random shocks to systems with stable equilibria. (ii) The intrinsic dynamics correspond to biennial cycles that are subject to stochastic forcing. (iii) Aperiodic fluctuations are intrinsic to the epidemiology. Comparison of real world data and epidemiological models suggests that measles epidemics are inherently chaotic. Conversely, the extent to which chickenpox outbreaks approximate a yearly cycle depends inversely on the population size.     

两种不同地理种群松毛虫赤眼蜂对米蛾卵的寄生功能及数值反应

【目的】松毛虫赤眼蜂(Trichogramma dendrolimi)是目前生物防治中应用面积最大的一种寄生性天敌。不同地理种群松毛虫赤眼蜂其生物学特性存在一定差异,论文旨在明确两种不同地理种群松毛虫赤眼蜂对米蛾卵的寄生功能反应及数值反应参数,为不同地理种群赤眼蜂的应用提供参考。【方法】选择松毛虫赤眼蜂黑龙江种群(TD-HLJ)和江苏种群(TD-JS),以米蛾卵为供试寄主,研究两个地理种群松毛虫赤眼蜂对米蛾卵的寄生功能反应与数值反应,并利用种群趋势指数(I)和干扰控制作用指数(IIPC)对两个不同地理种群松毛虫赤眼蜂进行分析比较。【结果】功能反应结果表明,TD-HLJ和TD-JS种群的寄生功能反应符合HollingⅡ型方程,TD-HLJ种群最大寄生量为186.78粒/d,比TD-JS的最大寄生量高75.68粒/d。数值反应研究表明,不同米蛾卵密度对松毛虫赤眼蜂TD-HLJ和TD-JS种群的寄生、发育及繁殖有显著影响,米蛾卵密度为1粒时是TD-HLJ和TD-JS种群羽化的临界值,米蛾卵密度为5和10粒时分别是TD-HLJ和TD-JS种群繁殖的临界值。采用I和IIPC分析松毛虫赤眼蜂的控制作用,TD-HLJ和TD-JS种群的I值均随着米蛾卵密度的增加而增加,对照TD-HLJ和TD-JS种群的I值分别为68.70和49.20,即TD-HLJ种群的下一代数量比TD-JS种群的数量多19.5倍;TD-HLJ和TD-JS种群的IIPC值均随着米蛾卵密度的增加而增加,说明随着卵密度的增加,TD-HLJ和TD-JS种群对寄主卵的控制作用逐渐减小。【结论】综合功能反应和数值反应结果,松毛虫赤眼蜂TD-HLJ种群比TD-JS种群具有更好的生物防治潜能。     

Regulatory role of parasites: impact on host population shifts with resource availability

Effects of infections by the ciliate Lambornella clarki on larval populations of its mosquito host Aedes sierrensis were examined in laboratory and field studies. When host populations developed with sufficient food, mortality from parasites was additive and reduced the number of emerging mosquitoes. For food-limited populations, mortality was compensatory or depensatory; emerging adults were as or more abundant with higher average fitness than those from uninfected control populations. When nutrients were scarce, parasitic infections relaxed larval competition and increased per capita food by reducing host abundance. Food limitation altered larval feeding behavior, reducing horizontal transmission and subsequent mortality from parasitism.     

豫综5号玉米综合种淀粉含量轮回选择效果分析

【目的】评价豫综5号玉米群体淀粉含量的改良效果,为创制高淀粉玉米种质资源、选育高淀粉玉米杂交种和继续改良豫综5号的淀粉含量提供依据。【方法】以提高玉米群体淀粉含量为目标,利用近红外技术对豫综5号群体完成了4轮的群体改良。以改良群体为父本,以黄早4、丹340、齐319、掖478和Mo17为测验种,采用NC-II遗传交配设计组配成20个测交组合。通过对不同轮次改良群体和20个测交组合在2个环境中的评价试验,对豫综5号群体淀粉含量轮回选择的改良效果进行了比较研究。【结果】豫综5号群体的淀粉含量随着改良轮次的增加呈逐渐提高的趋势,由C0的69.39%增加到C4的72.31%,4轮选择后淀粉含量实际增益为2.92%。同时蛋白质和赖氨酸含量呈逐轮下降趋势。随着改良轮次的增加,各测验种与各轮改良群体测交组合的淀粉含量逐轮提高,说明非破坏性单粒淀粉含量的轮回选择对豫综5号淀粉含量的改良是有效的;就一般配合力而言,随着改良轮次的增加,淀粉含量的一般配合力呈逐轮提高的趋势;从特殊配合力分析结果表明,黄早4与各轮群体间特殊配合力效应值逐轮提高,其它4个测验种与群体特殊配合力效应值呈现一定的波动。【结论】利用非破坏性单粒淀粉含量的轮回选择改良豫综5号淀粉含量是有效的,随着改良轮次的增加,豫综5号的淀粉含量逐渐提高。     

Legionella effectors that promote nonlytic release from protozoa

Legionella pneumophila, the bacterial agent of legionnaires' disease, replicates intracellularly within a specialized vacuole of mammalian and protozoan host cells. Little is known about the specialized vacuole except that the Icm/Dot type IV secretion system is essential for its formation and maintenance. The Legionella genome database contains two open reading frames encoding polypeptides (LepA and LepB) with predicted coiled-coil regions and weak homology to SNAREs; these are delivered to host cells by an Icm/Dot-dependent mechanism. Analysis of mutant strains suggests that the Lep proteins may enable the Legionella to commandeer a protozoan exocytic pathway for dissemination of the pathogen.     

桃果实单果重及可溶性固形物含量的全基因组选择分析

【背景】桃单果重和可溶性固形物含量（SSC）是育种家关注的两个重要的数量性状,受到多个微效基因的控制,难以通过单个标记进行早期筛选。全基因组选择作为一种新颖的数量性状早期预测工具,在果树上已经有了初步应用,但其在桃上的应用效果以及影响预测准确性的因素仍需要深入探讨。【目的】建立桃单果重和SSC的全基因组选择技术,为桃高效分子育种技术体系的建立奠定基础。【方法】以520株训练自然群体为试材,通过重测序筛选出的48 398个SNP进行分型,在11个全基因组预测模型中分别筛选出两个数量性状适宜的模型,进而在56株自然群体和1 145株杂交群体上进行应用。【结果】3类群体的平均测序数据量在1.95—3.52 Gb,测序深度为5.29—10.79×。训练自然群体经与参考基因组比对,共得到5 065 726个SNP,去除缺失率较高（>20%）、最小等位基因频率过低（<0.05）的位点后,随机挑选基因组上48 398个SNP用于训练群体的全基因组选择模型构建。单果重预测精度最高的模型是BayesA,SSC预测精度最高的模型为randomforest。分别利用两个数量性状最适的模型进行预测...     

不同轮回选择改良轮次玉米群体选系的育种潜势

【目的】研究18个从不同轮回选择改良轮次玉米群体中选育自交系的育种潜势,为玉米群体的有效改良及育种利用提供理论依据。【方法】以2个群体3个不同轮次改良后代中选育的高代自交系为材料,通过农艺性状表型鉴定、配合力测定和SSR分子标记遗传多态性分析的方法,对这些群体高代选系的育种潜势进行研究。【结果】改良群体高代选系产量和主要构成性状及其GCA表现优于基础群体高代选系,但多数改良群体高代选系株高、穗位高及其GCA都较各自的基础群体高代选系有所增加。不同群体高代选系之间,表型及配合力差异较大,来自同一群体不同基本株的选系之间差异也较大。SSR分析结果表明,改良群体高代选系在自交代数少1代的情况下,其纯合的位点比例与基础群体高代选系相当,与基础群体高代选系相比,改良群体高代选系间遗传差异虽有减小的趋势,但仍有较大的遗传差异。改良群体高代选系P4MSC2-1、P4MSC2-2、P5MSC2-2和P5MSC2-3以及基础群体高代选系P5C0-3,自身产量和主要性状及其GCA表现较好,与测验种所配组合产量较高,有较大的育种利用价值。【结论】群体高代选系的表型和配合力差异来源于不同群体及基本株的差异,从经过改良的群体中选育出的自交系表现更好,用改良群体选系纯合速度较快。     

桂综3号和桂苏综玉米群体相互轮回选择效果分析

【目的】对两个玉米群体桂综3号和桂苏综进行两轮相互轮回选择改良后的遗传效益进行评估,为其利用提供理论依据。【方法】以黄早4、掖478、丹340、M0174个测验种作母本,以两个玉米群体桂综3号和桂苏综不同改良群体作父本,按NCU遗传交配设计组配测交种,对各轮群体、群体间杂交组合和测交种进行田间鉴定,调查产量、株高、穗位高、穗长、穗粗、穗行数、行粒数、秃尖度、出籽率和千粒重并分析配合力等。【结果】桂综3号、桂苏综及其杂交组合产量平均每轮增益分别为83kg／ha（0．85％）、645kg／ha（12．45％）和390kg／ha（5．90％）;群体间杂交组合超亲优势从5．7％提高N13．5％。桂综3号的产量一般配合力效应从-5．32增加到-1．55,桂苏综的一般配合力效应从0．10增加到6．55。桂综3号、桂苏综均与掖478、丹340的特殊配合力都得到一定提高。出籽率和干粒重朝逐轮增加方向发展,秃尖度呈逐轮减少趋势,其他性状变化不明显。【结论】桂综3号和桂苏综经两轮相互轮回选择后,群体问杂交组合产量和杂种优势都逐轮增加,易与掖478、丹340等Reid、旅大红骨种质形成杂种优势模式,可继续进行相互轮回选择改良,利于在玉米育种上改良利用。     

Chromosome Changes Induced by Infections in Tissues of Rhynchosciara angelae

The main effects of two infections, one by a protozoan and the other by a virus, in cells of Rhynchosciara angelae (Diptera, Sciaridae) are an increase in cell size and changes in the size, shape, and behavior of the chromosomes. The X chromosome of some cells reacts differently from the autosome to the protozoan infection. Some chromosomes show specific, easily traceable points after infection by the virus. Some of the effects of these infections may be similar to the effects of infective agents in other organisms.     

Comparisons of Three Recurrent Selection Methods in the Improvement of Maize Populations

The maize population Csyn 4 was improved for three cycles with three recurrent selection methods MS1, MS1-HS, and MHSRRS in northern China. A total of 40 NC Ⅱ testcrosses were made by four testers with Csyn 4 and 10 improved populations, which were evaluated in four environments in the cropping season of 2005. Analysis of variance indicated a significant progress （P〈 0.05） in yield and other chief agronomic traits in the improved populations and testcrosses, demonstrating that the three recurrent selection methods were effective for increasing grain yield of testcrosses and improvement of general combining ability in maize population. The average grain yield increase of population Csyn 4 in MS1, MS1-HS, and MHSRRS recurrent selections was 266.7 kg ha^-1 （5.3%）, 288.0 kg ha^-1 （5.7%）, and 231.3 kg ha^-1 （4.6%） per cycle, while the grain yield of S 1 progeny of population for Csyn 4 was increased by 420.0 kg ha^-1 （10.9%）, 376.0 kg ha^-1 （9.8%）, and 414.7 kg ha^-1 （10.8%） per cycle in MS1, MS1-HS, and MHSRRS recurrent selections, respectively. Linear responses （b） in the MS1, MS1-HS, and MHSRRS recurrent selections were the same as the realized responses of the selection （G） for grain yield increase of Csyn 4 and S1 progeny of the populations. The grain yield of testcrosses increased by 3.3-5.2% on average per cycle. The value of heterosis did not display any differences amongst the different cycles of selections. The GCA for yield component traits of population Csyn 4 was improved significantly by means of three selection methods, whereas the GCA for plant height, ear height, days to silking, and days to pollen did not show significant increase in the recurrent selections. GCA for the number of tassel branches were decreased in the selections, while GCA for the number of plant leaves were increased, but the difference was not significant.     

Spatial pattern formation in an insect host-parasitoid system

Spatial models in ecology predict that populations may form patchy distributions within continuous habitats, through strong predator-prey or host-parasitoid interactions combined with limited dispersal. Empirical support of these models is provided. Parasitoids emanating from a population outbreak of tussock moths (Orgyia vetusta) suppressed the growth of nearby experimental populations of the moth, while experimental populations farther away were able to grow. This result explains the observed localized nature of tussock moth outbreaks and illustrates how population distributions can be regulated by dynamic spatial processes.     

7000 years of Emiliania huxleyi viruses in the Black Sea

A 7000-year record of Coccolithovirus and its host, the calcifying haptophyte Emiliania huxleyi, was reconstructed on the basis of genetic signatures preserved in sediments underlying the Black Sea. The data show that the same virus and host populations can persist for centuries. Major changes in virus and host populations occurred during early sapropel deposition, ~5600 years ago, and throughout the formation of the coccolith-bearing sediments of Unit I during the past 2500 years, when the Black Sea experienced dramatic changes in hydrologic and nutrient regimes. Unit I saw a reoccurrence of the same host genotype thousands of years later in the presence of a different subset of viruses. Historical plankton virus populations can thus be included in paleoecological and paleoenvironmental studies.     

Evolution of virulence in a plant host-pathogen metapopulation

In a wild plant-pathogen system, host resistance and pathogen virulence varied markedly among local populations. Broadly virulent pathogens occurred more frequently in highly resistant host populations, whereas avirulent pathogens dominated susceptible populations. Experimental inoculations indicated a negative trade-off between spore production and virulence. The nonrandom spatial distribution of pathogens, maintained through time despite high pathogen mobility, implies that selection favors virulent strains of Melampsora lini in resistant Linum marginale populations and avirulent strains in susceptible populations. These results are consistent with gene-for-gene models of host-pathogen coevolution that require trade-offs to prevent pathogen virulence increasing until host resistance becomes selectively neutral.     

An analog of myristic acid with selective toxicity for African trypanosomes.

Trypanosoma brucei, the protozoan parasite responsible for African sleeping sickness, evades the host immune response through the process of antigenic variation. The variant antigen, known as the variant surface glycoprotein (VSG), is anchored to the cell surface by a glycosyl phosphatidylinositol (GPI) structure that contains myristate (n-tetradecanoate) as its only fatty acid component. The utilization of heteroatom-containing analogs of myristate was studied both in a cell-free system and in vivo. Results indicated that the specificity of fatty acid incorporation depends on chain length rather than on hydrophobicity. One analog, 10-(propoxy)decanoic acid, was highly toxic to trypanosomes in culture although it is nontoxic to mammalian cells.     

不同种群云斑天牛对寄主取食和产卵的行为差异

【目的】研究不同种群云斑天牛Batocera horsfieldi对寄主植物的适应性。【方法】通过室内取食和产卵试验,测定余姚种群云斑天牛和临安种群云斑天牛对4种寄主植物(黄连木Pistacia chinensis、女贞Ligustrum lucidum、白蜡Fraxinus chinensis和大叶杨Populus lasiocarpa)的取食和产卵行为差异。【结果】取食试验结果显示:余姚种群云斑天牛与临安种群云斑天牛对4种寄主植物表现出不同的取食偏好性。余姚种群取食偏好性从高到低依次为黄连木、女贞、白蜡和大叶杨,余姚种群最喜欢取食黄连木。在选择性条件和无选择性条件下,取食量分别为(1 520.00±34.79)和(1 815.50±42.13) mm²。临安种群取食偏好性从高到低依次为女贞、黄连木、白蜡和大叶杨。临安种群最喜欢取食女贞,在选择性条件和无选择性条件下,取食量分别为(1 347.33±51.95)和(1 173.00±75.54) mm²。产卵结果试验显示:余姚种群和临安种群云斑天牛对4种寄主植物表现出比较一致的产卵偏好性,都...