Study of ectoparasitism of ultramicrobacteria of the genus <Emphasis Type="Italic">Kaistia</Emphasis>, strains NF1 and NF3 by electron and fluorescence microscopy

Transmission electron and fluorescence microscopy was used to study the character of the interaction of free-living ultramicrobacterial (UMB) strains NF1 and NF3, affiliated with the genus Kaistia, and seven species of gram-positive and gram-negative heterotrophic bacteria. Strains NF1 and NF3 were found to exhibit parasitic activity against gram-positive Bacillus subtilis and gram-negative Acidovorax delafildii. UMB cells are tightly attached to the envelopes of the victim cells and induce their lysis, thus demonstrating the features of typical ectoparasitism. The selectivity of parasitism of the studied UMB to the victim bacteria has been shown: only two soil microorganisms of the seven test objects, B. subtilis ATCC 6633 and an aerobic gramnegative bacterium A. delafildii 39, were found to be sensitive to UMB attack. Other bacteria (Micrococcus luteus VKM Ac-2230, Staphylococcus aureus 209-P, Pseudomonas putida BS394, Escherichia coli C 600, and Pantoea agglomerans ATCC 27155) were not attacked by UMB. It was established for the first time that free-living UMB may be facultative parasites not only of phototrophic bacteria, as we have previously demonstrated [1], but of heterotrophic bacteria as well. The UMB under study seem to play an important role in the regulation of the quantity of microorganisms and in the functioning of microbial communities in some natural ecotopes.     

Stochastic host-parasite interaction models

 We contribute to the discussion of causes and effects of aggregation (overdispersion) of macroparasite counts, focussing particularly upon the effects of clumped infections and parasite-induced host mortality. The simple nonlinear stochastic model for the evolution of the parasite load of a single host, investigated in Isham (1995), is extended to allow three parasite stages (larval, mature and offspring), and to allow durations of these stages to be non-exponentially distributed. As in the earlier work, exact algebraic results are possible, providing insight into the aggregation mechanisms, as long as the only source of interaction between host and parasites is an excess host mortality linearly related to the parasite load. Results are obtained on the distribution of parasite lad and on host survival. In particular, although parasite-induced host mortality is usually thought of as a process that reduces parasite aggregation (Anderson and Gordon 1982), it is shown that, for this model, parasite-induced host mortality cannot cause the index of dispersion to fall below unity. Host heterogeneity and disease control are also discussed. An approximation based on moment assumptions appropriate to a specially-constructed multivariate negative binomial distribution is proposed. This approximation, which is applicable to other processes, and an alternative based on the multivariate normal distribution are compared with exact results. Received: 17 December 1998 / Revised version: 2 June 1999     

Optical resolution by preferential crystallization of 4-methylpiperidinium hydrogen (RS)-phenylsuccinate

Gibbs energy of racemate formation, binary melting point diagram, and ternary solubility diagram suggested that 4-piperidinium hydrogen (RS)-phenylsuccinate [(RS)-4-MP salt] exists in a conglomerate. Appropriate conditions were explored on the basis of free energy of critical nucleation in a supersaturated solution to resolve efficiently (RS)-4-MP salt by preferential crystallization. Successive preferential crystallization of (RS)-4-MP salt in ethanol at 20°C gave (R)- and (S)-4-MP salts of 90–94% optical purities. Optically pure (R)- and (S)-phenylsuccinic acids were obtained by recrystallization of the (R)- and (S)-4-MP salts, followed by treatment of the salts purified with hydrochloric acid. © 1994 Wiley-Liss, Inc.     

Nonparametric estimation of the concordance correlation coefficient under univariate censoring

Assessing agreement is often of interest in clinical studies to evaluate the similarity of measurements produced by different raters or methods on the same subjects. Lin's (1989, Biometrics 45, 255-268) concordance correlation coefficient (CCC) has become a popular measure of agreement for correlated continuous outcomes. However, commonly used estimation methods for the CCC do not accommodate censored observations and are, therefore, not applicable for survival outcomes. In this article, we estimate the CCC nonparametrically through the bivariate survival function. The proposed estimator of the CCC is proven to be strongly consistent and asymptotically normal, with a consistent bootstrap variance estimator. Furthermore, we propose a time-dependent agreement coefficient as an extension of Lin's (1989) CCC for measuring the agreement between survival times among subjects who survive beyond a specified time point. A nonparametric estimator is developed for the time-dependent agreement coefficient as well. It has the same asymptotic properties as the estimator of the CCC. Simulation studies are conducted to evaluate the performance of the proposed estimators. A real data example from a prostate cancer study is used to illustrate the method.     

Multiscale ordination: a method for detecting pattern at several seales

Multivariate analyses of vegetation data have been restricted to a single scale of sampling, or multiscale sampling has been restricted to a single species. However, vegetation scientists need to be able to explore spatial relationships of many species over many scales. We present a modification of Noy-Meir & Anderson's (1971) method of multiscale ordination by summing two-term local covariance matrices and smoothing the component profiles. The advantages of our method are: 1) results are less subject to the starting position of the transect, 2) matrices may be added at any block size, and 3) plots of factor scores are smoothed by a moving weighted average to better reveal patterns at a prescribed scale.This procedure provides statistical associations of species over a range of scales. The scales which exhibit the association to the maximum extent are then determined from multiscale ordination. The relationships of different associations and their scales can then be examined. The application of the method to fabricated data proved successful in recovering the structure built into the data. When used on real vegetation data, from a community and a landscape, the method revealed the details of species associations over a range of scales, and of the relationships among associations.Abbreviations PCA = Principal Components Analysis - DCA = Detrended Correspondence Analysis - TTLC = Two-Term Local Covariance     

Relationship between genetic distance and heterosis for yield and morphological traits in winter canola (Brassica napus L.)

Genetic distance among canola cultivars was estimated through multivariate analysis. Thirty cultivars from various sources were analyzed and clustered based upon five morphological characteristics and yield components-crown diameter, number of branches plant^-1, number of pods plant^-1, number of seeds pod^-1 and yield plant^-1 -and placed in three distinct clusters. Two cultivars from each cluster were selected as parents and 15 partial-diallel inter- and intra-cluster crosses were made between the six selected parents and evaluated at two locations in Michigan in 1990/1991. The association between genetic distance and mid-parent heterosis was investigated. The correlation between genetic distance and heterosis was positive and highly significant for seed yield, number of pods plant^-1, and number of seeds pod^-1. Clustering, based on yield and yield-component traits, demonstrated that inter-cluster heterosis was greater than intra-cluster heterosis in the majority of cases.     

Organization of the lamin scaffold in the internal nuclear matrix of normal and transformed hepatocytes

Nuclear lamins are among the more abundant proteins making up the internal nuclear matrix, but very little is known about their structure in the nucleoplasm. Using immunoelectron microscopy, we demonstrate the organization of lamins in the nuclear matrix isolated from rat hepatocytes for the first time. Lamin epitopes are arrayed both in locally ordered clusters and in quasi-regular rows. Fourier filtering of the images demonstrates that the epitopes are placed at the nodes and halfway between the nodes of square or rhombic lattices that are about 50 nm on each side, as well as along rows at regular ∼25-nm intervals. In addition, we have compared this structure with that of the internal nuclear matrix isolated from persistent hepatocyte nodules. In transformed hepatocytes, the islands of lamin lattice are lost, and only a partial regularity in the rows of gold particles remains. We suggest that orthogonal lattice assembly might be an intrinsic property of lamin molecules, and that the disassembly may be triggered by simple molecular events such as phosphorylation.     

Habitat suitability modelling for Hirola (Beatragus hunteri) in Tsavo East National Park,Kenya

Hirola (Beatragus hunteri) is one of the most critically endangered antelope whose population is in decline, and its extinction might be the first loss of a mammalian genus in Africa since evolution of modern man. This decline has been attributed to, but is not limited to, habitat loss. Despite hirola introduction to Tsavo East National Park, its population has been stagnating at about 100 since 1996, and the reasons for this are not well documented. This research was aimed at determining the species’ distribution in relation to environmental variables. Data on the presence of hirola were collected between 2008 and 2011 through long‐term monitoring of hirola using aerial census and ground tracking. From this, a model was developed to predict the species’ habitat preferences. The model predicted that hirola preferred areas close to supplemented water, roads, seasonal rivers and water logged areas but avoided areas close to wooded grassland, tsetse infested and rapidly drained areas. This research concludes that hirola distribution depends on availability of fresh grass shoots, shade plants and tsetse‐free areas. To increase hirola carrying capacity in Tsavo East National Park, it calls for habitat manipulation through irrigation of rapidly drained areas, provision of supplemented water, prescribed burning and introduction of tsetse control strategies.     

Classification trees as an alternative to linear discriminant analysis

Linear discriminant analysis (LDA) is frequently used for classification/prediction problems in physical anthropology, but it is unusual to find examples where researchers consider the statistical limitations and assumptions required for this technique. In these instances, it is difficult to know whether the predictions are reliable. This paper considers a nonparametric alternative to predictive LDA: binary, recursive (or classification) trees. This approach has the advantage that data transformation is unnecessary, cases with missing predictor variables do not require special treatment, prediction success is not dependent on data meeting normality conditions or covariance homogeneity, and variable selection is intrinsic to the methodology. Here I compare the efficacy of classification trees with LDA, using typical morphometric data. With data from modern hominoids, the results show that both techniques perform nearly equally. With complete data sets, LDA may be a better choice, as is shown in this example, but with missing observations, classification trees perform outstandingly well, whereas commercial discriminant analysis programs do not predict classifications for cases with incompletely measured predictor variables and generally are not designed to address the problem of missing data. Testing of data prior to analysis is necessary, and classification trees are recommended either as a replacement for LDA or as a supplement whenever data do not meet relevant assumptions. It is highly recommended as an alternative to LDA whenever the data set contains important cases with missing predictor variables.     

Genetic parameters for producer-recorded health data in Canadian Holstein cattle

Health traits are of paramount importance for economic dairy production. Improvement in liability to diseases has been made with better management practices, but genetic aspects of health traits have received less attention. Dairy producers in Canada have been recording eight health traits (mastitis (MAST), lameness (LAME), cystic ovarian disease (COD), left displaced abomasum (LDA), ketosis (KET), metritis (MET), milk fever (MF) and retained placenta (RP)) since April 2007. Genetic analyses of these traits were carried out in this study for the Holstein breed. Edits on herd distributions of recorded diseases were applied to the data to ensure a sufficient quality of recording. Traits were analysed either individually (MAST, LAME, COD) or were grouped according to biological similarities (LDA and KET, and MET, MF and RP) and analysed with multiple-trait models. Data included 46 104 cases of any of the above diseases. Incidence ranged from 2.3% for MF to 9.7% for MAST. MET and KET also had an incidence below 4.0%. Variance components were estimated using four different sire threshold models. The differences between models resulted from the inclusion of days at risk (DAR) and a cow effect, in addition to herd, parity and sire effects. Models were compared using mean squared error statistic. Mean squared error favoured, in general, the sire and cow within sire model with regression on DAR included. Heritabilities on the liability scale were between 0.02 (MET) and 0.21 (LDA). There was a moderate, positive genetic correlation between LDA and KET (0.58), and between MET and RP (0.79).