Population dynamics and habitat connectivity affecting the spatial spread of populations – a simulation study

In this paper we show how the spatialconfiguration of habitat quality affects the spatial spread of apopulation in a heterogeneous environment. Our main result is thatfor species with limited dispersal ability and a landscape withisolated habitats, stepping stone patches of habitat greatlyincrease the ability of species to disperse. Our results showthat increasing reproductive rate first enables and thenaccelerates spatial spread, whereas increasing the connectivity has aremarkable effect only in case of low reproductive rates. Theimportance of landscape structure varied according to thedemographic characteristics of the population. To show this wepresent a spatially explicit habitat model taking into accountpopulation dynamics and habitat connectivity. The population dynamicsare based on a matrix projection model and are calculated on eachcell of a regular lattice. The parameters of the Leslie matrix dependon habitat suitability as well as density. Dispersal between adjacentcells takes place either unrestricted or with higher probability inthe direction of a higher habitat quality (restricted dispersal).Connectivity is maintained by corridors and stepping stones ofoptimal habitat quality in our fragmented model landscape containinga mosaic of different habitat suitabilities. The cellular automatonmodel serves as a basis for investigating different combinations ofparameter values and spatial arrangements of cells with high and lowquality.This revised version was published online in May 2005 with corrections to the Cover Date.     

Evaluation of the effectiveness of selected measures against bovine spongiform encephalopathy (BSE) in Switzerland by use of the basic reproduction ratio R0

The effectiveness of two measures against Bovine Spongiform Encephalopathy (BSE), the compulsory processing of animal by products to meat and bone meal (MBM) at 133 degrees C under 3 bars of pressure for 20 minutes in February 1993 and the exclusion of fallen stock, heads with eyes and spinal cord of cattle older than 30 month from MBM production in April 1996, was evaluated in a process model. The transmission of BSE by calculation of the basic reproduction ratio R0 was modelled.The results were verified by use of a cohort model, based on observed surveillance data. Prior to 1990, before the ban of feeding MBM to ruminants, R0, as calculated in the process model, was above 1, coherent with a slowly progressing BSE epidemic. Since 1991, values of R0 were low at 0.06.The corresponding R0 values derived from the cohort model were higher, the lowest value 0.13 calculated for 1996. Given such low R0 values, the epidemic should have died out. Additionally, no influence of the two measures was obvious at that time given the low level of R0. The discrepancy between the results of the two models is evidence for a dependency of the BSE epidemic from an infection source not considered in the process model. This infection source is most likely importation of feed ingredients and MBM.     

The effects of formulation on the immunostimulatory activity of dihydroheptaprenol

Holstein steer calves received a single injection of Miglyol (Sasol Chemical Industries, Ltd.) subcutaneously as a placebo, dihydroheptaprenol (DHP) (4 mg/kg) emulsified with lecithin subcutaneously, DHP in solution in Miglyol (4 mg/kg) subcutaneously, or DHP in solution in Miglyol (4 mg/kg) intranasally. The DHP emulsified in lecithin emulsion administered subcutaneously caused a substantial increase in body temperature, total leukocyte count, total neutrophil count, neutrophil cytochrome-c reduction, and neutrophil iodination 24 hours after administration and, for some of the parameters, at 48 hours. The DHP formulation in Miglyol did not have any of these effects when administered subcutaneously or intranasally. The carrier and formulation of DHP apparently have major effects on the biologic activity of DHP.     

Homogenization conditions affect the oxidative stability of fish oil enriched milk emulsions: oxidation linked to changes in protein composition at the oil-water interface

Fish oil was incorporated into milk under different homogenization temperatures (50 and 72 degrees C) and pressures (5, 15, and 22.5 MPa). Subsequently, the oxidative stability of the milk and changes in the protein composition of the milk fat globule membrane (MFGM) were examined. Results showed that high pressure and high temperature (72 degrees C and 22.5 MPa) resulted in less lipid oxidation, whereas low pressure and low temperature (50 degrees C and 5 MPa) resulted in faster lipid oxidation. Analysis of protein oxidation indicated that especially casein was prone to oxidation. The level of free thiol groups was increased by high temperature (72 degrees C) and with increasing pressure. Furthermore, SDS-PAGE and confocal laser scanning microscopy (CLSM) indicated that high temperature resulted in an increase in beta-lactoglobulin adsorbed at the oil-water interface. This was even more pronounced with higher pressure. Less casein seemed to be present at the oil-water interface with increasing pressure. Overall, the results indicated that a combination of more beta-lactoglobulin and less casein at the oil-water interface gave the most stable emulsions with respect to lipid oxidation.     

Mutations in U4atac snRNA, a component of the minor spliceosome, in the developmental disorder MOPD I

Small nuclear RNAs (snRNAs) are essential factors in messenger RNA splicing. By means of homozygosity mapping and deep sequencing, we show that a gene encoding U4atac snRNA, a component of the minor U12-dependent spliceosome, is mutated in individuals with microcephalic osteodysplastic primordial dwarfism type I (MOPD I), a severe developmental disorder characterized by extreme intrauterine growth retardation and multiple organ abnormalities. Functional assays showed that mutations (30G>A, 51G>A, 55G>A, and 111G>A) associated with MOPD I cause defective U12-dependent splicing. Endogenous U12-dependent but not U2-dependent introns were found to be poorly spliced in MOPD I patient fibroblast cells. The introduction of wild-type U4atac snRNA into MOPD I cells enhanced U12-dependent splicing. These results illustrate the critical role of minor intron splicing in human development.     

Displacement imaging in porous media using the line scan NMR technique

Displacement imaging is a recent, powerful NMR method with which distributions of displacements can be acquired of e.g. fluids within a porous medium. Both motion parallel and perpendicular to the flow direction may be observed within a time window of a few milliseconds to several seconds. By combining displacement imaging with the line scan technique, one-dimensionally resolved measurements with a high temporal resolution ( < 1 min) of the spatial dependency of motion can be obtained. Here we present displacement images of flow through two simple model systems for soil: an unconsolidated glass bead water system and a sintered glass bead filter. It is demonstrated that the combination of displacement imaging and spatial resolution along a line is important to access both bulk displacement and local displacements in relation to the local porosity.