Patterning of impoundment impact on chironomid assemblages and their environment with use of the self-organizing map (SOM)

The paper assesses the impact of the Jeziorsko dam reservoir on chironomid assemblages and selected environmental factors in the Warta River, Poland, by means of patterns recognized with the self-organizing map (SOM, Kohonen unsupervised artificial neural network). Over 1988–1996, in four annual cycles, a total of 233 monthly samples were collected in a seven order section of the river at two sites: WAA (backwater) located about 2 km upstream from the Jeziorsko Reservoir, and WAB (tailwater) located about 1.5 km downstream from the reservoir's dam. At each site three habitats were selected: H₁, H₂ and H₃ at WAA, and H₁₁, H₁₂ and H₁₃ at WAB. H₁ and H₁₁ were located in the depositional area close to the banks, H₂ and H₁₂ about 6–7 m towards the mid-river and H₃ and H₁₃ in the mid-river. SOM effectively vertically separated H₁ and H₁₁ (bank habitats) from H₃ and H₁₃ (the mid-river zone of both sites) and H₂ (the transition zone of the upstream site). The H₁₂ samples were scattered all over SOM but still exhibited a slight temporal gradient. At the end of the study the water discharge, especially in summers, stabilized at WAB at a level lower than natural and as a result submerged macrophytes appeared at H₁₂ making the abundance of macroinvertebrates increase very quickly. Moreover, a weaker horizontal grouping of samples by season and by site of collection (upstream or downstream from the reservoir) was observed over SOM: 1) bank upstream habitat H₁, with hydrological regime resembling natural, was separated from the downstream H₁₁, which enlarged and contracted in response to dam operation, 2) deeper habitats were less dependent on water level and this is why they underwent seasonal fluctuations. To sum up, the deepest habitats were most resistant to water level fluctuations, while the formerly most productive habitat at the tailwater WAB site, H₁₁, became the most negatively impacted. Nevertheless, the reservoir has not negatively influenced chironomid density, because the latter increased closer the mid-river, at H₁₂, where large patches of macrophytes developed.     

Rapid removal of unincorporated label and proteins from DNA sequencing reactions

This article presents a simple and rapid method for removal of unincorporated label and proteins from DNA sequencing reactions by using Wizard purification resin. This method can be successfully applied for preparation of end-labeled oligonucleotides free of unincorporated label, which is important in experiments (including DNA sequencing) when the level of background should be as low as possible. Also, this method is effective in removal of proteins from DNA sequencing reactions.     

The selection of aptamers specific for membrane molecular targets

A growing number of RNA aptamers have been selected experimentally using the SELEX combinatorial approach, and these aptamers have several advantages over monoclonal protein antibodies or peptides with respect to their applications in medicine and nanobiotechnology. Relatively few successful selections have been reported for membrane molecular targets, in contrast to the situation with non-membrane molecular targets. This review compares the procedures and techniques used in selections against membrane proteins and membrane lipids. In the case of membrane proteins, the selections were performed against soluble protein fragments, detergent-membrane protein mixed micelles, whole cells, vesicles derived from cellular membranes, and enveloped viruses. Liposomes were used as an experimental system for the selection of aptamers against membrane lipids. RNA structure-dependent aptamer binding for rafts in lipid vesicles was reported. Based on the selected aptamers against DOPC and the amino acid tryptophan, a specific passive membrane transporter composed of RNA was constructed. The determination of the selectivity of aptamers appears to be a crucial step in a selection, but has rarely been fully investigated. The selections, which use whole cells or vesicles derived from membranes, can yield aptamers not only against proteins but also against membrane lipids.     

Intramembranaceous ossification analyses by a proton microprobe

The proton induced X-ray emission method in combination with a proton microprobe was applied to study the intramembranaceous ossification. As material sections of mouse embryo skulls from the 17th and 19th day of gestation were used. The morphology of the sample was examined by routine histochemical procedure performed on the sections adjacent to that irradiated by the proton microprobe. The measurements were made in line scan and raster scan mode. The concentrations of P, S, Cl, K, Ca, Fe and Zn were determined at each irradiated point. The average element concentrations were calculated for four parts of each section (bone, cartilage, mesenchymal tissue close to the bone and mesenchymal tissue in other places). The distributions of Ca and P (less markedly than Ca) concentrations almost exclusively correlate with localization of the bone while S, Cl and K concentrations show preference to the cartilage. The amount of inorganic material in flat bones of the 17-day embryo amounts to 14% of the dry mass. The material is characterized by a Ca/P ratio of about 1.6. In the embryo 2 days older the amount of the inorganic phase is practically the same (15%) while the Ca/P ratio approaches 2. This suggests the presence of the precursor phase in the flat bone calcification. It is possible that octacalcium phosphate (Ca/P ratio equals to 1.72) is formed at the onset of the flat bone mineralization which transforms rapidly (in 2 days) to a more stable mineral (defective hydroxyapatite).     

LIFE-HISTORY CONSEQUENCES OF ADAPTATION TO LARVAL NUTRITIONAL STRESS IN DROSOPHILA

Many animal species face periods of chronic nutritional stress during which the individuals must continue to develop, grow, and/or reproduce despite low quantity or quality of food. Here, we use experimental evolution to study adaptation to such chronic nutritional stress in six replicate Drosophila melanogaster populations selected for the ability to survive and develop within a limited time on a very poor larval food. In unselected control populations, this poor food resulted in 20% lower egg‐to‐adult viability, 70% longer egg‐to‐adult development, and 50% lower adult body weight (compared to the standard food on which the flies were normally maintained). The evolutionary changes associated with adaptation to the poor food were assayed by comparing the selected and control lines in a common environment for different traits after 29–64 generations of selection. The selected populations evolved improved egg‐to‐adult viability and faster development on poor food. Even though the adult dry weight of selected flies when raised on the poor food was lower than that of controls, their average larval growth rate was higher. No differences in proportional pupal lipid content were observed. When raised on the standard food, the selected flies showed the same egg‐to‐adult viability and the same resistance to larval heat and cold shock as the controls and a slightly shorter developmental time. However, despite only 4% shorter development time, the adults of selected populations raised on the standard food were 13% smaller and showed 20% lower early‐life fecundity than the controls, with no differences in life span. The selected flies also turned out less tolerant to adult malnutrition. Thus, fruit flies have the genetic potential to adapt to poor larval food, with no detectable loss of larval performance on the standard food. However, adaptation to larval nutritional stress is associated with trade‐offs with adult fitness components, including adult tolerance to nutritional stress.