Geographical gradients of stability in European land bird communities

Summary European data from 15 long-term censuses of breeding land bird communities were analysed in order to measure community stability. Stability was here operationally defined as year-to-year persistence of community structure (total density, number of species, diversity, evenness of the species-abundance distribution, species list, and frequencies of species). Central Europe and southern Scandinavia formed a zone of fairly stable communities, but more northern communities were fairly unstable. This result contrasts with several recent arguments, but accords well with the classic dogma that instability of biological communities increases northwards in the northern hemisphere.Three theoretical explanations for the difference in stability between northern and southern communities were explored, and causal mechanisms underlying the hypotheses were specified and tested. Considerable evidence supported the hypothesis that environmental (climatic) unpredictability increases northwards and mainly causes the phenomenon observed. Gradients in productivity may, perhaps in interaction with unpredictability, also contribute to geographical differences in stability, but tests suggested that low diversity is not an important cause of northern instability.     

Moisture content and CO2 exchange of lichens. II. Depression of net photosynthesis in Ramalina maciformis at high water content is caused by increased thallus carbon dioxide diffusion resistance

Summary Thalli of Ramalina maciformis were moistened to their maximal water holding capacity, thus, simulating actual conditions following a heavy rainfall. Time courses of net photosynthesis at 17° C and 750 E m^-2 s^-1 light intensity (PAR) were obtained during drying of the thalli. At ambient CO₂ concentrations from 200 to 1,000 ppm, CO₂ uptake of the moist lichens was depressed at high water content. After a certain water loss, net photosynthesis increased to a maximal value and decreased again with further drying of the thalli. The degree of initial depression of photosynthesis decreased with increasing ambient CO₂ concentration, and it was fully absent at 1,600 ppm ambient CO₂. Under these conditions of CO₂ saturation, net photosynthesis remained constant at maximum for many hours and decreased only when substantial amounts of water had been lost. We conclude that the carboxylation capacity of the lichen is not affected by high contents of liquid water. Therefore, the depression of CO₂ uptake of the water saturated lichen at lower (e.g. natural) ambient CO₂ must be due exclusively to increased resistance to CO₂ diffusion from the external air to the sites of carboxylation.     

Comparison of Different Agar Diffusion Methods for the Detection of Antimicrobial Residues in Slaughter Animals

The different agar diffusion methods were compared using antibiotic and sulphonamide-impregnated filter-paper discs and the kidneys of healthy and emergency-slaughtered pigs and cows after slaughter. No method used seemed to be sensitive to all antimicrobial drugs preimpregnated onto discs. Tetracycline yielded a greater zone of inhibition at pH 6 than at pH 8 and aminoglycosides, erythromycin, polymyxin B and lin cornycin at pH 8 than at pH 6. It therefore seems necessary to use different pHs (6 and 8). The addition of trimethoprim to the medium is necessary for the detection of sulphonamides. Bacillus subtilis BGA used as the test organism was more sensitive to sulphonamides on the “Test agar for the inhibitor test” containing trimethoprim than on the “Iso-Sensitest agar” also containing trimethoprim. The addition of trimethoprim to “Test agar for the inhibitor test” is recommended at pH 8 but not at pH 6 because false-positive cases (with inhibition zones > 2 mm) were observed at pH 6 with trimethoprim on the kidneys of healthy pigs.     

Long-term population changes of the most abundant south Finnish forest birds during the past 50 years

Summary 1. Population indices based on bird censuses (especially line transects) are given for south Finnish forest birds (40 species). The indices refer to 1926–27, 1936, 1936–49, 1952–63 and 1973–77.2. Population increases were observed to be much more frequent than decreases. The main reason for the changes is presumably that the structure of the Finnish forests has changed considerably in recent decades. Many bird populations are thus probably well adapted to habitat changes caused by forestry. However, certain species need habitats destroyed by modern forestry (e. g. old forests); in consequence, it is necessary to maintain sufficient old forests areas for conservational purposes.

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Zusammenfassung 1. Für die 40 häufigsten Waldvögel Südfinnlands werden, meist auf der Grundlage von Linientaxierungen, Populationsindices ermittelt. Diese Indices beziehen sich auf die Jahre 1926/27, 1936, 1936–49, 1952–63 und 1973.2. 22 Arten (Gruppe A der Tabelle) haben eindeutig zugenommen. Die Gründe hierfür sind wohl in Veränderungen der Struktur finnischer Wälder zu suchen, nämlich Zunahme der Fläche von Jungbeständen, der Ausdehnung der Strauchschicht in Altbeständen, der Bedeutung der Fichte als Waldbestandteil und schließlich der Waldränder.3. 7 Arten (Gruppe B) nahmen einheitlich zu mit Ausnahme im SW-Teil des Landes, wo die Zunahme sehr gering war. Diese Arten scheinen in gleicher Weise von den Strukturänderungen finnischer Wälder beeinflußt worden zu sein wie die in Gruppe A. Doch wiesen diese 7 Arten schon 1926/27 im SW Finnlands relativ hohe Dichten auf. Da alle Arten dieser Gruppe hauptsächlich im Süden verbreitet sind, bedeutet die Zunahme in Finnland, daß offenbar die meisten Arten dieser Gruppe ihr Areal nach Norden ausdehnten, was schließlich zu einem deutlichen Populationsanstieg im Untersuchungsgebiet führte.4. 7 Arten (Gruppe C) zeigten keine deutlich erkennbaren Trends. Die Erklärung hierfür scheint in hohen jährlichen Fluktuationen der Populationsgröße als auch in möglichen interspezifischen Konkurrenzverhältnissen zu suchen zu sein.5. 4 Arten (Gruppe D) nahmen deutlich ab, wahrscheinlich in erster Linie infolge der Abnahme des Flächenanteils alter Waldbestände oder der zunehmenden Schwierigkeiten, alte Bäume zu finden.6. So wurden also Zunahmetendenzen weit häufiger als Abnahmetendenzen festgestellt. Diese Ergebnisse stimmen mit anderen Untersuchungen von langfristigen Bestandstrends nordeuropäischer Vogelarten überein. Sie weisen ferner daraufhin, daß offenbar viele Vogelpopulationen an die Habiate, die durch moderne Forstwirtschaft entstehen, gut angepaßt sind. Jedoch sollten diese Ergebnisse vom Standpunkt des Naturschutzes aus nicht falsch interpretiert werden. Sinn des Naturschutzes ist nicht, die Populationsgröße sehr häufiger Arten positiv zu beeinflussen, sondern die Abnahme der Populationsgrößen bedrohter Arten zu verhindern. In diesem Zusammenhang sei auf die Notwendigkeit des Schutzes genügend großer Flächen alter Waldbestände hingewiesen, da eine Reihe von Arten davon im höchsten Maße davon abhängig sind.

     

Overexpression of VEGF in Testis and Epididymis Causes Infertility in Transgenic Mice: Evidence for Nonendothelial Targets for VEGF

Vascular endothelial growth factor (VEGF) is a key regulator of endothelial growth and permeability. However, VEGF may also target nonendothelial cells, as VEGF receptors and responsiveness have been detected for example in monocytes, and high concentrations of VEGF have been reported in human semen. In this work we present evidence that overexpression of VEGF in the testis and epididymis of transgenic mice under the mouse mammary tumor virus (MMTV) LTR promoter causes infertility. The testes of the transgenic mice exhibited spermatogenic arrest and increased capillary density. The ductus epididymidis was dilated, containing areas of epithelial hyperplasia. The number of subepithelial capillaries in the epididymis was also increased and these vessels were highly permeable as judged by the detection of extravasated fibrinogen products. Intriguingly, the expression of VEGF receptor-1 (VEGFR-1) was detected in certain spermatogenic cells in addition to vascular endothelium, and both VEGFR-1 and VEGFR-2 were also found in the Leydig cells of the testis. The infertility of the MMTV-VEGF male mice could thus result from VEGF acting on both endothelial and nonendothelial cells of the male genital tract. Taken together, these findings suggest that the VEGF transgene has nonendothelial target cells in the testis and that VEGF may regulate male fertility.     

HIGH ENCYSTMENT SUCCESS OF THE DINOFLAGELLATE SCRIPPSIELLA CF. LACHRYMOSA IN CULTURE EXPERIMENTS 1

Close to 100% encystment efficiency and a yield above 10⁵ cysts·mL ^{? 1} were routinely achieved in full strength f/2 medium‐based batch cultures (883 μM NO₃ ^? and 36 μM PO₄ ^{? 3}) of the marine dinoflagellate Scrippsiella cf. lachrymosa Lewis. Increases in cell density led to nutrient depletion in this enriched medium, which was the most likely cause for initiation of cyst formation. Lowering the concentration of either nutrient to 1/10 the initial levels decreased the encystment efficiency, whereas use of ammonium as the N source resulted in both low cell yield and low encystment efficiency. The mandatory dormancy period was ca. 60 days and was not affected by cold dark storage of the cysts. Cysts produced in the initial phase of sexual reproduction were relatively large (length 47 μm, width 31 μm) with a heavy calcareous cover. Cysts produced thereafter lacked apparent calcareous cover and were smaller (length 29 μm, width 19 μm). The decrease of cyst volume (by a factor of 0.24–0.4) suggested strong resource limitation during the course of encystment. However, after the mandatory dormancy period, germination success of the smaller cysts was higher (80%), compared with the larger cysts that had been produced initially (50%). Germling survival (74%) was independent of cyst type but was enhanced by higher nutrient concentration during incubation. The ratio of initial nutrient concentration in the medium to the cyst yield was used as a proxy to estimate the cellular nutrient quota. The conservative estimates of 9 pmol N·cyst ^{? 1} and 0.4 pmol P·cyst ^{? 1} obtained in this manner are at the low end of the range of previous published estimates for other dinoflagellate cysts. Given the high encystment observed in laboratory experiments, we have no reason to assume an inherently lower encystment success in dinoflagellate field populations. Our results do not challenge the low nutrient paradigm for dinoflagellate sexuality. We believe that the high encystment success and cyst yield of this particular species is at least partly due to its ability to achieve very high cell densities in cultures, which evidently leads to nutrient depletion even in f/2 medium.     

The level of autoantibodies against oxidized LDL is not associated with the presence of coronary heart disease or diabetic kidney disease in patients with non-insulin-dependent diabetes mellitus

Oxidation of low-density lipoprotein (LDL) may be an important factor in the development of diabetic macrovascular and renal complications. The level of autoantibodies against oxidized LDL (oxLDL-Ab) can be used as an index of LDL oxidation in vivo. The purpose of this study was to investigate the association between the level of oxLDL-Ab and the presence of coronary heart disease and renal dysfunction in patients with non-insulin-dependent diabetes mellitus (NIDDM). We determined the plasma levels of oxLDL-Ab in 46 NIDDM patients and 48 well matched non-diabetic control subjects. NIDDM patients had a moderately higher level of oxLDL-Ab than control subjects (0.083 ± 0.051 vs. 0.062 ± 0.045, p = 0.04). However, there was no difference in the level of oxLDL-Ab between subjects with and without coronary heart disease, and the level of oxLDL-Ab was not associated with indices of glomerular filtration rate or urinary albumin excretion.     

Scanning electron microscopic examination of Thiobacillus ferrooxidans on different support matrix materials in packed bed and fluidized bed bioreactors

Summary Thiobacillus ferrooxidans was used in fixed-film bioreactors to oxidize ferrous iron to ferric iron. The test support matrix materials included activated carbon particles, glass beads, and ion-exchange resin particles. The experimental systems included a fluidized bed approach, which was evaluated with activated carbon only, and a packed bed approach which was tested with each of the support matrix materials. The colonization of the matrix surface was examined with scanning electron microscopy. There were contrasting differences in the bacterial colonization and accumulation of Fe(III) precipitates on the matrix surface among the test materials. The packed bed activated carbon bioreactor displayed the fastest kinetics and the highest amount of cell sorption as well as the roughest and most porous matrix surface.     

Missing value imputation improves clustering and interpretation of gene expression microarray data

Background  

Missing values frequently pose problems in gene expression microarray experiments as they can hinder downstream analysis of the datasets. While several missing value imputation approaches are available to the microarray users and new ones are constantly being developed, there is no general consensus on how to choose between the different methods since their performance seems to vary drastically depending on the dataset being used.