Can transposable element copy number distribution parameters be estimated from natural populations of Drosophila melanogaster?

The copy frequency distribution of a transposable element family in a Drosophila melanogaster natural population is generally characterised by the values of the Charlesworths' model parameters α and β (Charlesworth & Charlesworth, 1983). The estimation of these parameters is made using the observed distribution of the occupied sites in a population sample. Several results have been interpreted as due either to the influence of stochastic factors or to deterministic factors (transposition, excision, selection…). The accuracy of this method was tested by estimations performed on samples from simulated populations. The results show that with the sample size usually used for natural population studies, the confidence intervals are too large to reasonably deduce either the element copy number distribution or the values of transposition and excision rate and selective coefficients.     

Seemingly Unrelated Generalized Linear Models

By using deviance standardized residuals, the seemingly unrelated regression estimation procedure is extended to generalized linear models, and fitted by an iterative procedure. The matrix of cross products of standardized residuals is asymptotically multivariate normal, and can be used for further multivariate analyses and for hypothesis testing.     

Desert ants Cataglyphis fortis use self-induced optic flow to measure distances travelled

While foraging, desert ants of the genus Cataglyphis use a vector navigation (route integration) system for homing. Any vector navigation system requires that the animal is able to evaluate the angles steered and the distances travelled. Here we investigate whether the ants acquire the latter information by monitoring self-induced optic flow. To answer this question, the animals were trained and tested within perspex channels in which patterns were presented underneath a transparent walking platform. The patterns could be moved at different velocities (up to > 0.5 the ant's walking speed) in the same or in the opposite direction relative to the direction in which the animal walked. Experimental manipulations of the optic flow influenced the ant's homing distances (Figs. 2 and 4). Distance estimation depends on the speed of self-induced image motion rather than on the contrast frequency, indicating that the motion sensitive mechanism involved is different from mechanisms mediating the optomotor response. Experiments in which the ants walked on a featureless floor, or in which they wore eye covers (Fig. 6), show that they are able also to use additional (probably kinesthetic) cues for assessing their travel distance. Hence, even though optic flow cues are not the only ones used by the ants, the experiments show that ants are obviously able to exploit such cues for estimation of travel distance.     

A Random Field Approach to Transect Counts of Wildlife Populations

Line transect counting of a wildlife population is considered a sampling from a planar marked point process, where the marks describe the detectability of the animals. Sampling properties of transect counts and a new density estimator are derived from a counting process, which is a shot-noise field induced by the marked point process. A general formula for the sampling variance of a transect is derived and applied to compare five common types of transects. Some stereological connections of transect sampling and density estimators are shown.     

The Use of Proton Chemical Shifts to Define the Solution Structure of a Dimeric Peptide

For flexible peptides, nuclear Overhauser Effects (NOE) experiments do not provide enough information to ensure a correct definition of their solution structure. The use of distance constraints, derived from the knowledge of proton chemical shifts, is developed to restrict the number of possible conformations. In the case of flexible molecules, randomization appears as an important factor of the correct estimation of the chemical shifts from the 3D structure. The refinement of the solution structure of the highly flexible AVP-like parallel dimer is described to illustrate this process.     

Assessing the Effect of the Best Treatment. A Non-parametric Inference Problem

For patients of a certain type, a number of treatments are available. The effect of each such treatment is assumed to be described by a shift model; it is, however, admitted that there may be an interaction between patient and treatment, meaning in particular that the treatment which is best for one patient is not necessarily best for another. The problem is the following: if each patient is given the treatment which is optimal for that particular patient, will this produce a significant effect and, if so, how large is the effect?     

Tests for Trends in Incidence Rate Ratios

Breslow (1984) described an efficient score test for trend in incidence density rate ratios for cohort studies under a conditional Poisson or binomial model employing maximum likelihood estimation of the rate parameters. In this communication, an alternative derivation of this statistic that is based on an unconditional approach is provided, along with an examination of associated goodness-of-fit tests and methods of confidence interval estimation. The procedures are illustrated by a cohort study of ischemic heart disease mortality following industrial exposure to carbon disulfide.