四种蕨类植物根际土壤中VA菌根真菌孢子种群组成和季相变化

对４ 种移栽到温室中的蕨类植物根际土壤中的ＶＡ 菌根真菌孢子种群组成和季相变化进行了研究, 结果发现, ＶＡ菌根真菌孢子的产生具有明显的宿主依赖性和季相变化。在相同气候条件下, 不同植物根际土壤中的ＶＡ菌根真菌种群组成不同; 同种ＶＡ 菌根真菌在不同宿主植物根际土壤中, 孢子的丰富度有很大的差异。本文对影响ＶＡ菌根真菌孢子种群组成和季相变化的因素进行了讨论。     

The regulation of the dynamics of human populations

The important aspects of population dynamics are shown in a model along with the changes of population structure, the reasons for these changes and the conditions under which such changes take place. Subsequently, the reasons for these population dynamic processes which can be arranged in a three step scale are shown. Here, it must be differentiated between endogenous processes, due to factors inherent in the population, and exogenous ones caused by external forces effecting structural changes. The population political trends has to be incorporated as a part of the exogenous factors. The questions of regularities in the population dynamics are shown in the examples of important population theories in history. At the same time the theoretically possible borders are described, within which, due to purely physiological reasons, a population dynamic process has to occur. However, these borders will never be reached. Examination of the inertia of the population dynamic processes suggests an examination of the questions about the probability of the self-destructive processes in population dynamics. Considering the strong self-regulatory processes within a population the hypothesis of a population extinction is refuted.     

Estimation of the Number of Classes in a Population

The problem of estimating M, the number of classes in a population, is formulated as an occupancy problem in which N items are drawn from M urns. Under the assumption of a uniform distribution for the number of classes in the population, the sufficient statistic for M, which is the number of distinct classes observed, does not depend upon the number of repetitions in the sample. Point and interval estimates of M are developed using maximum likelihood and the method of moments. Both techniques give rise to the same basic equation which requires a simple iterative solution. These same techniques are used in the more general situation in which the classes can be further subdivided according to type.     

Anthropometry and the biological structure of the Hvar population

Biological structure of the population of the island of Hvar was investigated by using the data on anthropometric variation among nine village populations; 24 body and 14 head dimensions were analysed from 487 male and 437 female adult subjects. Univariate and multivariate analyses revealed heterogeneity among the populations, which says much for the strength of the isolating factors on the island. Using correlations of anthropometric and geographic distance, the observed patterns of variation among villages were closely related to geography, suggesting migration to be an important factor in the formation of the island's population structure. Populations of the examined villages were further grouped to form the population of the eastern part and the population of the western part of the island, which have an ethnodemographic and sociocultural basis. The analyses revealed heterogeneity between the populations and thus provided evidence to support the hypothesis about the existence of the genetically different groups living in the same biotope.     

On the phosphorus budget of a perennial herbSolidago altissima population

The same methods were used to study the phosphorus budget of aSolidago altissima population on the flood plain of the Tone River as were used for the nitrogen budget studies. The standing crop of phosphorus and the phosphorus flow through the population were determined seasonally and annually. The annual absorption of phosphorus was 2.25 g/m²/year, which is the same as the annual return to the environment. Turnover rates of phosphorus were calculated. Whether expressed seasonally or annually, turnover rates of phosphorus were larger than those of nitrogen. Phosphorus utility, net dry matter productivity of a unit amount of phosphorus absorbed, in this population was 1,060. This was in the range reported on other perennial herb communities. Phosphorus cycling in the population was quantified. Total phosphorus input to organs and the amount of phosphorus recycled in the living plants were 3.67 g/m²/year and 1.42 g/m²/year, respectively. The proportion of recycling to the total movement of phosphorus in the plant was 39%, which was lower than that of nitrogen. Comparing the phosphorus and nitrogen budgets in the population, it was concluded that larger recycling of an element results in a smaller turnover rate of the element in the population.     

Estimation of the amount of inbreeding due to subdivision of a population

In a large population which is subdivided into isolated or partially isolated subpopulations polymorphic for a gene locus, there is an excess of homozygotes due to the subdivision. This excess increases with the variance of the gene frequency. The excess can be measured by the “coefficient of inbreeding.” The aim of this paper is to estimate this coefficient, which is a function of various population parameters. We suggest several different estimates, which are the same functional form of unbiased estimates of the population parameters. These estimates are shown to be consistent. They have been compared by numerical methods among themselves and with two other estimates suggested previously.     

Measurement of the intraspecific variation in population growth rate under controlled conditions in the clonal parthenogen Daphnia magna

Clones of parthenogenetically reproducing females of Daphnia magna were developed from females derived from the same wild population. Significant differences were found between the population growth rates of such clones under controlled conditions. Such variation showed no clear relationship to electrophoretic differences at the GOT and esterase-1 loci between the clones. The extent to which such variation represents fitness variation in the wild population from which the animals were derived is considered. Methods are proposed for potentially distinguishing between possible causes of negative correlations between fitness components by studying the effects of such components upon total fitness.     

Density dependence and the control of helminth parasites

1. The transient dynamics and stability of a population are determined by the interplay between species density, its spatial distribution and the positive and negative density-dependent processes regulating population growth. 2. Using the human-helminth parasite system as an example, we propose that the life-stage upon which negative density dependence operates will influence the rate of host reinfection following anthelmintic chemotherapy, and the likely success of control programmes. 3. Simple deterministic models are developed which highlight how a parasite species whose population size is down-regulated by density-dependent establishment will reinfect a host population at a faster rate than a species with density-dependent parasite fecundity. 4. Different forms of density dependence can produce the same equilibrium behaviour but different transient dynamics. Under-representing the nature and magnitude of density-dependent mechanisms, and in particular those operating upon establishing life-stages, may cause the resilience of the parasite population to a control perturbation to be underestimated.     

Changing of the dynamics modes in populations with age and sex structure

Using a mathematical model of the number dynamics in a population with age and sex structure, the relationships were studied between the number of newborns and that of mature females and males. In addition, we studied transitions between different modes of population dynamics which were dependent on changes in not only the population parameters, such as reproduction intensity, survival, and self-regulation, but also in mating pair formation. Population dynamics was found to manifest multistability; i.e., the alternative dynamics modes were observed at the same values of the population parameters but under different initial conditions.     

The genetics of transient populations: Research at the metapopulation level

The metapopulation concept allows us to generate new models, in which each single local population is in disequilibrium (from both demographic and genetic points of view) but the whole is stable. We review recent empirical and theoretical results showing the relevance of the metapopulation level, in particular for understanding the evolution of those traits that do not experience the same selective forces during the different demographic stages of each local population.     

Variation in the life-span of clones derived from human diploid cell strains

The doubling potential of several hundred clones derived from WI-38 and WI-26 cell cultures has been determined. Clones were isolated at various population doubling levels (PDLs) during the finite in vitro life-span of the mass (uncloned) cultures. In all cases, there was a large variation in population doubling potential (or life-span) among the clones isolated from a single mass culture. When clones were isolated from mass cultures which had undergone eight or nine population doublings, only about 50% of the clones were capable of more than eight population doublings. This percentage was further reduced when clones were isolated from mass cultures at higher PDLs. Mass cultures appear to be composed of two subpopulation classes: one with a low population doubling potential, and the other with a higher population doubling potential. Nevertheless, the highest doubling potential observed in clones isolated from any single culture was about the same as the doubling potential of the mass culture from which single cells were taken.     

Paleogenetics of the late Roman-early Byzantine cemeteries at Sayala,Egyptian Nubia

Out of the five late Roman-early Byzantine cemeteries at Sayala, the three large burial complexes CI-III were found to represent the same population not only on the basis of 76·6% of the metric features already studied, but also of 72·9% of the 48 non-metric features examined in the present paper. The remaining features, which show different frequencies, were most probably related to some social and/or genetic isolation of the three subgroups (“lineages”) of the same basic population.The left-right asymmetry of the frequencies was practically irrelevant; sex differences were however present in one-third of the features observed.Some of the traits showed unusually high frequencies, revealing a high rate of inbreeding within a homogeneous population.To evaluate the relationships among the CI-III people and the neighbouring populations, 22 discrete traits were compared with the same traits studied in 11 Ancient Egyptian samples by Berry, Berry & Ucko (1967) and in 6 contemporary African Negro samples by Rightmire (1972). It was shown that the Sayala CI-III population does not resemble either of these groups. The fourth contemporary Sayala sample from A cemetery was also found to be not related with the CI-III sample on the basis of the same traits. The fifth contemporary Sayala sample from N cemetery was too small to be tested. Moreover, the comparison between the CI-III population and the C-group population of Sayala also revealed the lack of genetic continuity. The isolated position found in the CI-III population of Sayala agrees with the hypothesis that it would represent the Blemmyes, people originating from the Eastern Desert.     

Utility of Microcosm Studies for Predicting Phylloplane Bacterium Population Sizes in the Field

Population sizes of two ice nucleation-active strains of Pseudomonas syringae were compared on leaves in controlled environments and in the field to determine the ability of microcosm studies to predict plant habitat preferences in the field. The P. syringae strains investigated were the parental strains of recombinant deletion mutant strains deficient in ice nucleation activity that had been field tested for their ability to control plant frost injury. The population size of the P. syringae strains was measured after inoculation at three field locations on up to 40 of the same plant species that were studied in the growth chamber. There was seldom a significant relationship between the mean population size of a given P. syringae strain incubated under either wet or dry conditions in microcosms and the mean population size which could be recovered from the same species when inoculated in the field. Specifically, on some plant species, the population size recovered from leaves in the field was substantially greater than from that species in a controlled environment, while for other plant species field populations were significantly smaller than those observed under controlled conditions. Population sizes of inoculated P. syringae strains, however, were frequently highly positively correlated with the indigenous bacterial population size on the same plant species in the field, suggesting that the ability of a particular plant species to support introduced bacterial strains is correlated with its ability to support large bacterial populations or that indigenous bacteria enhance the survival of introduced strains. Microcosm studies therefore seem most effective at assessing possible differences between parental and recombinant strains under a given environmental regime but are limited in their ability to predict the specific population sizes or plant habitat preferences of bacteria on leaves under field conditions.     

Population dynamics of the African elephant (Loxodonta africana)

Recent studies on elephant populations from East Africa and from Zambia have suggested that as population density increases, so does the mean age at puberty and the mean calving interval. At the same time there is also an increase in the proportion of old females that are reproductively inactive. By constructing elephant population models, it is possible to investigate the extent to which these "homeostatic mechanisms" will regulate an elephant population. The models indicate that a change in the duration of the calving interval is more important as a population regulating mechanism than a change in the age at puberty, and that the proportion of old reproductively inactive females is of little significance. The importance of neonatal mortality in controlling population growth is emphasised by the models, and they also show that an annual population increase of 4% would be close to the maximum value.     

Estimating the distribution of selection coefficients from phylogenetic data with applications to mitochondrial and viral DNA

The distribution of selection coefficients of new mutations is of key interest in population genetics. In this paper we explore how codon-based likelihood models can be used to estimate the distribution of selection coefficients of new amino acid replacement mutations from phylogenetic data. To obtain such estimates we assume that all mutations at the same site have the same selection coefficient. We first estimate the distribution of selection coefficients from two large viral data sets under the assumption that the viral population size is the same along all lineages of the phylogeny and that the selection coefficients vary among sites. We then implement several new models in which the lineages of the phylogeny may have different population sizes. We apply the new models to a data set consisting of the coding regions from eight primate mitochondrial genomes. The results suggest that there might be little power to determine the exact shape of the distribution of selection coefficient but that the normal and gamma distributions fit the data significantly better than the exponential distribution.     

The Quasispecies for the Wright–Fisher Model

We consider the classical Wright–Fisher model of population genetics. We prove the existence of an error threshold for the mutation probability per nucleotide, below which a quasispecies is formed. We show a new phenomenon, specific to a finite population model, namely the existence of a population threshold: to ensure the stability of the quasispecies, the population size has to be at least of the same order as the genome length. We derive an explicit formula describing the quasispecies.     

大白菜细胞核复等位雄性不育基因定位

以大白菜不育材料"939A"为母本,携带恢复基因的材料YDQ56A为父本构建隐性雄性不育F1S4分离群体,利用混合分组分析法(BSA)对不育基因初定位;同时以"939A"为母本,携带保持基因的材料yellow sason为父本构建显性雄性不育F2分离群体,对不育基因进行精细定位。结果在F1S4群体中获得与不育基因连锁的标记2个,A08_1900和Br ID111035,与不育基因分别相距8.8c M和2.5c M,物理距离为804.1kb;F2群体中不育单株与可育单株分离比符合3∶1,不育基因表现为显性。通过标记验证,F2和F1S4两个群体定位结果一致,均位于A08染色体末端,通过新标记的筛选获得不育基因两侧紧密连锁的标记Br19470306和Br19675586,与不育基因分别相距1.6c M和2.4c M,物理距离205.28kb,其中包含58个基因。该结果为大白菜雄性不育系的利用以及转育奠定了基础。     

微分方程在描述两群体进化过程中的应用

为了解释生物进化各种过程,在一定的条件下,通过定向选择推导出的微分方程可以研究两个共享同一资源但同时又互不杂交的同类群体的进化过程。虽然人们的直觉是大群体往往能占有生存的良机,但是这种认识是片面的。通过微分方程的各种模拟结果可以得出结论：一方面在简单的适应面上,即当一个群体发生有利突变而产生具有优势的后代,那么无论初始条件如何这个群体将最后侵蚀掉另一群体。大群体因有利突变等概率产生而有更大的几率获得生存的优势。另一方面在略微复杂的适应面上,如果两个群体都发生有利突变只是发生的时间不同。在相同的境遇下,小群体相比大群体反而有更大的可能存活下来而不被灭绝。     

内蒙古和林格尔土城子农业人群与林西井沟子游牧人群股骨中部的生物力学对比

肢骨的形态结构可以反映人类进化、古代人群的生存适应性活动和生存环境等重要信息。基于“骨骼功能适应”和“杠杆原理”,有学者对不同生计方式的古代人群下肢股骨开展了大量的研究工作,但是,国内外尚未有关于农业人群和游牧人群股骨之间差异性研究的报道。本文选取两个具有代表性的古代人群,即内蒙古和林格尔土城子戍边农业人群和内蒙古林西井沟子游牧人群进行对比研究。通过对股骨骨干中部横断面生物力学分析发现,农业人群股骨粗壮度与游牧人群之间具有显著差异。前者的平均粗壮度较大,后者女性组下肢骨的活动强度明显较小,这可能与游牧人群经常从事骑马活动而下肢骨活动强度相对较少有关。农业人群股骨指数的变异范围均大于游牧人群,这可能与前者男性的士兵身份有关;同时,也提示土城子男性组股骨所反映的行为活动信息并不代表真正意义上的纯农业人群下肢骨行为模式,而是一种农业和士兵行为的混合模式。在性别分工上,井沟子组的男女性均从事骑马活动,两侧股骨受力较为一致,在两侧不对称性程度和骨干横断面形状上的男女差异不大;男性股骨的粗壮度要明显大于女性,这与井沟子组男性还从事一定的狩猎行为有关。与游牧人群女性较为纤细的股骨不同,土城子组女性作为典型的农业人群代表,其下肢骨整体的活动强度较大,几乎与同组的男性和井沟子组男性相当,组内的性别差异相对较小;骨干横断面形状的显著性差异说明,土城子组内部男性和女性的行为活动方式存在明显的性别分工。本文研究结果说明农业人群女性的下肢骨活动强度较大,在行为活动方式上,戍边农业人群具有更为明显的性别分工。