Which locus has the oldest allele?

This paper studies aspects of the distribution of non-mutant ancestors of a sample of gametes in a two-locus infinitely-many-alleles model. The ancestral process of two gametes is considered in detail. Included are algorithms for calculating the probability that the oldest allele is from the first locus, and the expected age of the oldest allele. Extensions to an r-locus model in the cases of complete linkage and independence are also studied.     

Semiterrestrial meiofauna inhabiting a wet campo in central Brazil, with special reference to the Copepoda (Crustacea)

The wet campo (campo úmido) marsh type is widely distributed in the cerrado region of central Brazil. These marshes develop on slopes along margins of gallery forests where the water table persists at or near the soil surface year-round. Their grass and sedge vegetation covers spongy, highly organic (not peaty) soils. Ground and surface water seeping through the wet campos tends to be slightly acidic (pH about 5), ion-poor (conductivity less than 10 µS cm^–1) and well oxygenated.A typical freshwater meiofaunal community develops in those wet campos where soils remain moist throughout the year (moisture content more than about 60% of soil wet weight). Such a community was studied from 1979–1982 in a wet campo in a protected natural area on the Fazenda Água Limpa of the Universidade de Brasília. It was dominated by nematodes, rotifers and harpacticoid copepods, and included protozoans, turbellarians, cyclopoid copepods, cladocerans, ostracods, oligochetes, hydracarines and several families of aquatic insect larvae. This community was most fully developed in the wetter areas.Species richness of the copepod community is the highest yet recorded in a freshwater system. The 29 species of harpacticoid copepods and 4 species of cyclopoid copepods displayed pronounced zonation which seemed best correlated with soil moisture content and water regime.     

The chemistry of wet deposition for a tallgrass prairie ecosystem: inputs and interactions with plant canopies

The chemistry and nutrient inputs of wet deposition, and the N chemistry of throughfall, were characterized for a tallgrass prairie in north-central Kansas. Dominant ions in wetfall were NH ₄ ⁺ , Ca²⁺, H⁺, NO ₃ ^- , and SO ₄ ^2- ; weighted mean pH was 4.79. Principal sources of ions appeared to be natural emissions and wind-blown soils. Concentrations of NO ₃ ^- -N, NH ₄ ⁺ -N, and organic N in wet deposition were 0.31, 0.30, and 0.17 mg/L, respectively, resulting in N inputs of 2.5, 2.5, and 1.4 kg · ha^-1 · yr^-1. Comparisons with bulk precipitation suggested that at least 50% of atmospheric N inputs were from dry deposition. Concentrations of NO ₃ ^- -N, NH ₄ ⁺ -N, and organic N in unburned prairie throughfall were 0.27, 0.28, and 1.28 mg/L, and in burned prairie throughfall were 0.33, 0.37, and 0.91 mg/L, respectively. The prairie canopy intercepted up to 48% of incident precipitation. Lower inorganic N and higher organic N concentrations in throughfall relative to wet deposition probably resulted from leaf uptake of N and immobilization by microbes associated with the standing dead plant materials of the prairie canopy. The removal of these materials by fire is important in maintaining N availability for tallgrass prairie. Much of the N immobilization appeared to have been of N that was supplied to the prairie canopy by dry deposition.     

Outer acrosomal membrane of guinea pig spermatozoa: Isolation and structural characterization

We describe a protocol to isolate a highly enriched fraction of outer acrosomal membrane from guinea pig spermatozoa and present new data on the ultrastructure of this membrane domain. Cauda epididymal spermatozoa were suspended into a low ionic strength buffer and subjected to brief homogenization; this stripped the plasma membrane from the spermatozoa and severed the acrosomal apical segment from the spermatozoon. The crescent-shaped apical segments retained the outer acrosomal membrane and specific components of the acrosomal matrix. Enriched fractions of apical segments were isolated on discontinuous sucrose gradients and the outer acrosomal membrane purified by subsequent centrifugation onto Percoll density gradients. The isolated outer acrosomal membrane did not form vesicles, but instead rolled up into spiral sheets. Both thin section and negatively stained specimens revealed a paracrystalline arrangement of filaments associated with the luminal surface of the membrane. The isolated outer acrosomal membrane revealed a limited number of polypeptides by SDS-PAGE, and the polypeptide pattern was distinct from the plasma membrane fraction. The isolated acrosomal membranes possessed no oubain sensitive Na+, K+-ATPase activity, whereas about 20% of the ATPase activity of the plasma membrane enriched fraction was inhibited by oubain. The potential function of the structural differentiations of the outer acrosomal membrane in the membrane fusion events of the acrosome reaction is discussed.     

Fractionation of K-562 cells on the basis of their surface properties by partitioning in two-polymer aqueous-phase systems

The K-562 cell line is a culture of human leukemia stem cells originally derived from a patient with chronic myelogenous leukemia in blast crisis. We have subjected such cells, in the log phase of growth, to countercurrent distribution in a charge-sensitive dextran-polyethylene glycol aqueous-phase system, a method that fractionates cells on the basis of subtle differences in their surface properties, and found that: (1) The cell population is heterogeneous since it is composed of cells with different partition ratios. (2) There is a correlation between increasing cell partition ratios and increasing cell electrophoretic mobilities. (3) Cells under different parts of the distribution curve have dissimilar ratios of cells in different parts of the cell cycle, a phenomenon that may, at least partially, be the basis for the subfractionation of these cells. There is a clear tendency for cells in G₀+G₁+early S to decrease and for those in late S+G₂+M to increase with increasing partition ratios. (4) Sialic acid is a major surface charge component of the cells as evidenced by a dramatic drop in their partition ratios after treatment with neuraminidase.     

Structure of primary Japanese beech (Fagus japonica maxim.) forests in the Chichibu Mountains,central Japan,with special reference to regeneration processes

The floristic composition, structure and dynamics of three primaryFagus japonica stands were investigated in the Chichibu Mountains.F. japonica was dominant [RD(%): 64.9–87.0] and showed a slightly inverse J-shaped DBH class distribution in the quadrats [No. of canopy stems (H>20m): 87–138/ha]. The stems ofF. japonica for each size were distributed in the form of colonies, being scattered almost uniformly, and arranged in positive association with each other. Detailed examination of the bases of the stem groups forming colonies revealed that most of them originated from the bases of dead mother stems and that they were from common stools [No. of large stems (H>10 m) per stool: 6–11]. Among six major canopy gaps observed, only one included stems sprouting from the outer part ofF. japonica stools, while all the others were occupied by individuals of species other thanF. japonica. After tree-fall, several undercanopyF. japonica stems remained. Thus canopy gaps in these forest stands recovered through the sprouting of remainingF. japonica stools or by new sprouting ofF. japonica individuals adjacent to the gaps. However, it was considered difficult to fill canopy gaps only with sprouts when the distance between the center of a gap and that of a stool surpasses the crown vector. Such places that are not fully occupied by sprouts will be filled by individuals of other canopy and/or under-canopy species.     

生态系统的天气环境模拟模型

无论对于自然的还是人为管理的生态系统,天气都是最重要的一种环境条件。用系统分析方法对生态系统进行的研究使天气模拟越来越成为非常必要的了。本文首先介绍了一个美国天气模拟模型(WGEN)的数学原理。它用马尔柯夫链和Γ-分布组成降水量子模型,产生逐日降水量。用弱平稳过程和调和分析为工具建立另一个子模型,产生逐日最高温度、最低温度和太阳辐射量。通过常规的统计学方法或灰靶白化方法可以估计模型参数。于是,就可由WGEN生出Alabama州天气模型ALWGEN和北京天气模型BJWGEN。考虑到篇幅有限,本文没有具体介绍上述估计方法,也只是扼要介绍了用Monte Carlo Bootstrap方法进行模型校验和验证的问题。最后,简单地讨论了天气模拟模型的应用。如IPM研究中的风险分析,生态系统管理决策,农业生态区域规划等课题,对天气模型都有现实的或潜在的需要。     

时间序列谱分析在作物究研中的应用探讨(一)

本文分两个部分分别探讨了单一和两维时间序列谱分析在研究作物量变过程规律中的意义、应用的原理和方法,并通过实例结果的分折表明这些方法的可行性,所揭示的生物学意义和这些方法的应用在研究作物量变过程中将可能具有的广泛的研究前景。     

Tracheole migration in an insect wing

Summary Insect tissues are supplied with oxygen by a system of long and highly branched cuticular tubes known as tracheae and tracheoles. During the growth of with imaginal discs in moths and butterflies, tracheole cells migrate distally from the base of the disc. Tracheoles radiate in a distal direction through the extracellular space sandwiched between the upper and lower epithelial surfaces of the wing.Migration of most cells is assumed to be governed by forces intrinsic to the cell. However, the movement of tracheoles is apparently a passive process whose motive force resides in adjacent epithelial cells. After epithelial cells are exposed to ecdysteroid hormones, these cells extend basal processes that are attracted to oxygen-rich tracheoles. By applying traction to the tracheoles with which they establish intimate contact, epithelial cells may control the pattern of their distribution within wing tissue.