Demography in stochastic environments. I. Exact distributions of age structure

The steady state distribution of age structure is studied for populations with two age classes and stochastic vital rates. For a serially uncorrelated dichotomic vital rate the distribution of age structure is found analytically to be a singular steplike function; outside a specific region of vital rate values the singular function crosses a threshold to a smooth function. For a vital rate following a correlated two state Markov process the joint distributions of age structure and environment are found analytically to be singular steplike functions; again a threshold marks a transition to a smooth function. For fecundities which are serially uncorrelated but continuously distributed the age structure distribution is obtained as a smooth analytic function for all parameter values. These explicit results have applications to studies of age structure and average growth rate.     

CLIX: a search algorithm for finding novel ligands capable of binding proteins of known three-dimensional structure.

A computer algorithm, CLIX, capable of searching a crystallographic data-base of small molecules for candidates which have both steric and chemical likelihood of binding a protein of known three-dimensional structure is presented. The algorithm is a significant advance over previous strategies which consider solely steric or chemical requirements for binding. The algorithm is shown to be capable of predicting the correct binding geometry of sialic acid to a mutant influenza-virus hemagglutinin and of proposing a number of potential new ligands to this protein.     

The biofilm architecture of sixty opportunistic pathogens deciphered using a high throughput CLSM method

This study proposes a high throughput method based on Confocal Laser Scanning Microscopy (CLSM) combined with the use of 96-wells microtiter plates compatible with high resolution imaging for the study of biofilm formation and structure. As an illustration, the three-dimensional structures of biofilms formed by 60 opportunistic pathogens were thus observed and quantified. The results revealed the diversity of biofilm architectures. Specific spatial arrangement such as the mushroom-like structures already described for Pseudomonas aeruginosa was observed. Other features, such as hollow voids in microcolonies of Salmonella enterica strain Agona, were identified for the first time. The combined use of microplates and confocal imaging proved to be a good alternative to the other high throughput methods commonly used as it enables the direct, insitu, qualitative and quantitative characterization of biofilm architecture. This high content method should lead to a clearer understanding of the structure-function relationships implicated in biofilms traits.     

How Many Seed Transfer Zones Are Necessary for the Preservation of the Genetic Identity of Austrocedrus chilensis Natural Populations in Argentina?

Two different studies based on isozymes that include genetic structure analysis have arrived at contrasting conclusions regarding the minimum number of seed transfer zones for Patagonian cypress (Austrocedrus chilensis) in Argentina that are required in order to avoid genetic contamination in restoration programs. Unfortunately, the more recent article lacks discussion on these controversial results, which is, therefore, the purpose of this article. The reliability of the markers used and the sampling performed in these studies are evaluated comparatively. The later study found higher levels of diversity and differentiation but paradoxically suggested that only two seed transfer zones would be enough to preserve the genetic identity of the natural populations of the species, whereas the earlier study concluded that at least five are necessary. Arguments are presented here for the case that definition of fewer than five genetically homogeneous groups is absolutely inappropriate and implies a probable risk of genetic contamination and maladaptation.