Are environmental factors responsible for geographic variation in the sex ratio of the Greenlandic seed‐bug Nysius groenlandicus?

Until recently nothing indicated an unequal sex ratio in the widespread Greenland seed‐bug Nysius groenlandicus (Zetterstedt) (Heteroptera: Lygaeidae). However, recently populations more or less devoid of males were discovered in high arctic Northeast Greenland. This initiated an inspection of the entire material of the species collected in Greenland and now preserved at the Zoological Museum, University of Copenhagen. It was found that the sex ratio varied significantly among different locations. In most cases females were most abundant, but males were either scarce or absent only in samples from Northeast Greenland, indicating that here the species reproduces asexually. This paper demonstrates that the differing sex distributions can be explained by climatic factors (temperature, precipitation) and that the degree of continentality (distance from the open sea) promotes female‐biased sex ratios.     

Is topmouth gudgeon Pseudorasbora parva responsible for the decline in sunbleak Leucaspius delineatus populations?

In England, a severe decline of introduced sunbleak Leucaspius delineatus populations has been attributed to the introduction of the invasive topmouth gudgeon Pseudorasbora parva . In France, however, after 4 years of P. parva colonization in a large natural lake, no demonstrated impacts on the native L. delineatus populations have been observed. This suggests that the original impacts observed in England, such as spawning inhibition and high mortality, were the result of an emerging pathogen, the rosette-like agent, hosted by L. delineatus rather than P. parva .     

Environmental factors responsible for switching on the SO₄²⁻ excretory system in the kidney of seawater eels

Eels are unique in that they maintain lower plasma SO(4)(2-) concentration in SO(4)(2-)-rich (～30 mM) seawater (SW) than in SO(4)(2-)-poor (<0.3 mM) freshwater (FW), showing drastic changes in SO(4)(2-) regulation between FW and SW. We previously showed that the expression of renal SO(4)(2-) transporter genes, FW-specific Slc13a1 and SW-specific Slc26a6a, changes profoundly after transfer of FW eels to SW, which results in the decrease in plasma SO(4)(2-) concentration after 3 days in SW. In this study, we attempted to identify the environmental factor(s) that trigger the switching of SO(4)(2-) regulation using changes in plasma and urine SO(4)(2-) concentrations and expression of the transporter genes as markers. Transfer of FW eels to 30 mM SO(4)(2-) or transfer of SW eels to SO(4)(2-)-free SW did not change the SO(4)(2-) regulation. Major divalent cations in SW, Mg(2+) (50 mM) and Ca(2+) (10 mM), were also ineffective, but 50 mM NaCl was effective for switching the SO(4)(2-) regulation. Further analyses using choline-Cl and Na-gluconate showed that Cl(-) is a primary factor and Na(+) is permissive for the Cl(-) effect. Since plasma SO(4)(2-) and Cl(-) concentrations were inversely correlated, we injected various solutions into the blood and found that Cl(-) alone triggered the switching from FW to SW-type regulation. Furthermore, the inhibitor of Na-Cl cotransporter (NCC) added to media significantly impaired the expression of SW-specific Slc26a6a in 150 mM NaCl. In summary, it appears that Cl(-) ions in SW are taken up into the circulation via the NCC together with Na(+), and the resultant increase in plasma Cl(-) concentration enhances SO(4)(2-) excretion by the kidney through downregulation of absorptive Slc13a1 and upregulation of excretory Slc26a6a, resulting in low plasma SO(4)(2-) concentration in SW.     

Are snake populations in widespread decline?

Long-term studies have revealed population declines in fishes, amphibians, reptiles, birds and mammals. In birds, and particularly amphibians, these declines are a global phenomenon whose causes are often unclear. Among reptiles, snakes are top predators and therefore a decline in their numbers may have serious consequences for the functioning of many ecosystems. Our results show that, of 17 snake populations (eight species) from the UK, France, Italy, Nigeria and Australia, 11 have declined sharply over the same relatively short period of time with five remaining stable and one showing signs of a marginal increase. Although the causes of these declines are currently unknown, we suspect that they are multi-faceted (such as habitat quality deterioration, prey availability), and with a common cause, e.g. global climate change, at their root.     

Are the same Compounds in Microcystis responsible for Toxicity to Daphnia and Inhibition of its Filtering Rate?

Three strains of Microcystis when supplied to Daphnia in mixtures with Scenedesmus differed in their power to inhibit filtering rates. The axenic strain PCC 7806 had the strongest effect (93% inhibition with 50% Microcystis in the food). This strain was toxic to daphnids since Daphnia died faster under these conditions than without any food. Strain PCC 7806 also exhibited strong toxicity against mice (LD₅₀ 22 mg/kg). When the toxicity against Daphnia and mice was tested with cells of Microcystis PCC 7806 which has been subjected to various extraction procedures, the extraction of freeze-thawed cells with water slightly reduced the mouse toxicity, eliminated Daphnia toxicity and reduced the inhibition of the filtering rate. After treatment with a lipophilic solvent, the cells of PCC 7806 still showed low mouse toxicity, but no longer inhibition of the filtering rate and no toxicity to Daphnia. Thus, our data suggest that Daphnia toxicity and inhibition of the filtering rate are caused by different compounds, but we cannot rule out the possibility that the factors toxic to mice and inhibitory to the filtering rate are identical.     

Are microRNAs responsible for cardiac hypertrophy in fish and mammals? What we can learn in the activation process in a zebrafish ex vivo model

Recent studies have correlated dysregulated miRNA expression with diseased hearts. With the aim of developing an easily manipulated experimental model, phenylephrine (PE) was added to cultured zebrafish hearts to study the expression of miR1 and miR133a by qRT-PCR. Both miRs were downregulated, with greater downregulation leading to higher hypertrophy. The involvement of this miRs was confirmed by the in-vivo inoculation of complementary sequences (AmiR1 and AmiR133a). HSP70 (involved in transporting proteins and in anti-apoptosis processes) was increased in both treatments. Hyperplasia was observed in the epicardium based on WT1 expression (embryonic epicardial cell marker) in both the PE treatment and AmiR133a treatment. The treatment with AmiR1 showed only cardiomyocyte hypertrophy. This ex-vivo model revealed that miR1 and miR133a play a key role in activating early processes leading to myocardium hypertrophy and epicardium hyperplasia and confirmed the expected similarities with hypertrophic disease that occurs in humans.     

Are biotic factors significant in influencing the distribution of halophytes in saline habitats?

The influence of biotic factors on the distribution and establishment of halophytes is being considered in this review. Physicochemical factors, such as salinity and flooding, often are considered to be the determining factors controlling the establishment and zonational patterns of species in salt marsh and salt desert environments. Sharp boundaries commonly are found between halophyte communities even though there is a gradual change in the physicochemical environment, which indicates that biotic interactions may play a significant role in deterining the distribution pattern of species and the composition of zonal communities. Competition is hypothesized to play a key role in determining both the upper and lower limits of species distribution along a salinity gradient. Field and laboratory experiments indicate that the upper limits of distribution of halophytes into less saline or nonsaline habitats is often determined by competition. There appears to be a reciprocal relationship between the level of salt tolerance of species and their ability to compete with glycophytes in less saline habitats. Halophytes are not competitive in nonsaline habitats, but their competitive ability increases sharply in saline habitats. Allelopathic effects have been reported in salt desert habitats, but have not been reported along salinity gradients in salt marshes. Some species of halophytes that are salt accumulators have the ability to change soil chemistry. Chemical inhibition of intolerant species occurs when high concentrations of sodium are concentrated in the surface soils of salt desert plant communities that are dominated by salt-accumulating species. Establishment of less salt-tolerant species is inhibited in the vicinity of these salt-accumulating species. Herbivory is reported to cause both an increase and a decrease in plant diversity in salt marsh habitats. Heavy grazing is reported to eliminate sensitive species and produce a dense cover of graminoids in high marsh coastal habitats. However, in other marshes, grazing produced bare patches that allowed annuals and other low marsh species to invade upper marsh zonal communities. A retrogression in plant succession may occur in salt marshes and salt deserts because of heavy grazing. Intermediate levels of grazing by sheep, cattle, and horses could produce communities with the highest species richness and heterogeneity. Grazing by geese produced bare areas that had soils with higher salinity and lower soil moisture than vegetated areas, allowing only the more salt-tolerant species to persist. Removal of geese from areas by use of inclosures caused an increase in species richness in subarctic salt marshes. Invertebrate herbivores could also inhibit the survival of seeds and the ability of plants to establish in marshes. Parasites could play a significant role in determining the species composition of zonal communities, because uninfected rarer species are able to establish in the gaps produced by the death of parasitized species.     

Are hydrophobins and/or non-specific lipid transfer proteins responsible for gushing in beer? New hypotheses on the chemical nature of gushing inducing factors

Gushing of beer is characterised by the fact that immediately after opening a bottle a great number of fine bubbles are created throughout the volume of beer and ascend quickly under foam formation, which flows out of the bottle. This infuriating gushing phenomenon has been, and still is, a problem of world-wide importance to the brewing industry. It is generally assumed that the causes of malt-derived gushing are due to the use of "weathered" barley or wheat and the growth of moulds in the field, during storage and malting. We now develop a hypothesis connecting several lines of evidence from different laboratories. These results indicate that the fungal hydrophobins, hydrophobic components of conidiospores or aerial mycelia, are gushing-inducing factors. Furthermore, increased formation of ns-LTPs (non-specific lipid transfer proteins), synthesised in grains as response to fungal infection, and their modification during the brewing process may be responsible for malt-derived gushing.     

Are changes in breeding habitat responsible for recent population changes of long-distance migrant birds?

Capsule: The direction and magnitude of changes in structure of UK woodlands since the 1980s, are inconsistent with them playing a causative role in the declines of four migrant bird species in upland oak woods.

Aims: To investigate whether changes in woodland structure were a possible cause of population changes of four Afro-Palearctic migrants (Wood Warbler Phylloscopus sibilatrix, Tree Pipit Anthus trivialis, Pied Flycatcher Ficedula hypoleuca and Common Redstart Phoenicurus phoenicurus) in the upland oakwoods of western and northern Britain.

Methods: Bird population estimates and measures of woodland structure were recorded in two time periods 1982–85 and 2003–04 across six regions of the UK. We modelled the effect of habitat change and initial habitat state on population changes between the two time periods. The predicted effects of habitat change on populations were then compared with observed population changes across the different regions.

Results: All four species underwent population declines; there were also significant increases in ground cover and understorey cover. The number of birds in 2003–04 was influenced by habitat structure at this time in addition to showing regional differences. Change in bird numbers varied between regions and was affected by both the initial habitat state and change in habitat structure, with regional variation in the effect of habitat change. There was however no relationship between the predicted effect of change in habitat structure on population size and observed regional population changes.

Conclusions: Changes in woodland structure are unlikely to be the main driver of population change in these four migrant bird species, and large-scale factors affecting demographics in other parts of their breeding range or in their wintering areas are likely reasons for local population declines.     

Are lipid phase transitions responsible for chilling damage in human platelets?

In previous studies we have proposed that the well-known chilling-induced activation of human blood platelets can be ascribed at least in part to a thermotropic phase transition in membrane lipids. The evidence that this is the case is reviewed and amplified in this review, followed by an examination of the available physical data concerning phase transitions in lipid mixtures that mimic the mixture found in platelet membranes. Assuming complete mixing at all temperatures and equal contributions of the members of the mixture to the phase transition, the lipid mixture found in platelets should give values for Tm ranging from about 1 degrees C to about 16 degrees C, depending on the isomers present in the mixture. (The former value is not in agreement with the observed Tm, but the latter is in excellent agreement.) However, examination of the phase diagram for a binary pair of lipids found in platelet membranes shows that ideal mixing almost certainly does not occur; instead of a linear phase diagram, a convex one was obtained. This shape for the phase diagram, which would displace Tm to an unexpectedly elevated temperature, is in agreement with previously published phase diagrams for mixtures of this type. The prediction, based on thermodynamic properties of lipids found in the platelets, is that Tm will be displaced upward in more complex mixtures of the composition found in platelets, a prediction that requires experimental testing.     

Is glucokinase responsible for the anomeric specificity of glycolysis in pancreatic islets?

At a low concentration of D-glucose (3.3 mM), the phosphorylation rate of this hexose in rat pancreatic islet homogenates incubated at 8 degrees C is higher with the beta- than with the alpha-anomer, as expected from the anomeric specificity of hexokinase. In the presence of a high concentration of glucose 6-phosphate (3.0 mM), which inhibits hexokinase but not glucokinase, the phosphorylation rates of the two anomers are not significantly different from one another. Nevertheless, in intact islets exposed at 8 degrees C to the same low concentration of D-glucose, the alpha-anomer augments, more than the beta-anomer, the production of lactic acid and net uptake of 45Ca. At the same concentration (3.3 mM), the alpha-anomer is also more potent than the beta-anomer in enhancing insulin release from perfused pancreases stimulated at 37 degrees C by L-leucine or by the combination of Ba2+ and theophylline. It is concluded that the participation of glucokinase is not essential for the anomeric specificity of glycolysis and insulin release in rat pancreatic islets.     

Is selection responsible for the low level of variation in the last intron of the ZFY locus?

DNA variability was investigated in the last intron of the Y-chromosome-specific zinc finger gene, ZFY, and its X homolog on Xp21.3, ZFX. No polymorphisms were found in the 676-bp ZFY segment in a sample of 205 world-wide-distributed Y chromosomes, other than a solitary nucleotide variant in one individual (nucleotide diversity pi = 0.0014%). In contrast, 10 segregating sites (pi = 0.082%) were identified within 1,089 bp of the ZFX sequence in a sample of 336 X chromosomes. Four of these polymorphisms, which contributed most of the diversity, were located within an Alu insert disrupting the ZFY-ZFX homology (pi Alu = 0.24%). The diversity in the homologous portion of the ZFX intron, although higher than that in ZFY, was lower than that found in genomic segments believed to evolve neutrally; interspecies divergence in both segments was also reduced. Although this suggests that the evolution of both ZFY and ZFX homologs may not be entirely neutral, both Tajima and HKA tests did not reject neutrality. The lack of statistical significance may be attributed to a lack of power in these tests (the low divergence and variability values reduce the power of the HKA and Tajima tests, respectively); furthermore, Homo sapiens has recently undergone a rapid population growth, and selection is more difficult to detect in an expanding population. Therefore, the failure to reject neutrality does not necessarily indicate the absence of selection. In this context, the phylogenetic argument was given more weight in out interpretations. The high level of sequence identity in ZFY and ZFX segments, in spite of their separation 80-130 MYA, reflects a lower mutation rate as compared with other segments believed to undergo unconstrained evolution. Thus, the possibility of weak selection contributing to the low level of nucleotide diversity in the last ZFY intron cannot be excluded and should be kept in mind in the population genetics studies based on Y chromosome variability.     

Exploiting the apoptotic process for management of HIV: Are we there yet?

CD4⁺ T cells die in individuals infected with HIV, either as a result of direct HIV infection or as uninfected innocent bystanders. Possible mechanisms for bystander killing include generation of viral products such as Tat or gp120 and expression of death receptor ligands, such as FasL, that engage functional death receptors on uninfected cells. This review covers the sometimes conflicting in vitro and ex vivo studies that address these possible mechanisms of HIV-associated cell death. It is an intriguing possibility that manipulation of cell death processes, to decrease bystander death or increase death of infected cells, in patients infected with HIV might provide a useful adjunct to antiretroviral therapy.     

Are the short-photoperiod-induced decreases in serum prolactin responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters?

Serum prolactin (PRL) decreases in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters following short-photoperiod exposure. Both species also exhibit short-photoperiod-induced changes in body and lipid mass, but in opposite directions; Syrian hamsters increase and Siberian hamsters decrease their body weight, changes reflected nearly exclusively in their carcass lipid content. The purpose of these experiments was to determine whether the photoperiod-induced changes in PRL were responsible for the seasonal changes in energy balance in Syrian and Siberian hamsters by using the strategy of experimentally producing serum PRL levels opposite to those normally associated with the photoperiod in which the animals were housed. In long photoperiods serum PRL was reduced to short-day levels by subcutaneous (s.c.) CB-154 (bromoergocryptine, a dopamine agonist) injections. In short photoperiods, serum PRL was elevated to long-day levels in Syrian hamsters by ectopic pituitary explants, and in Siberian hamsters, serum PRL was elevated by chronic s.c. infusions of ovine PRL (oPRL). In both species, manipulations of serum PRL did not affect food intake, carcass composition, or the wet weight of various white and brown adipose tissue pads (WAT and BAT, respectively). Body weight increased in CB-154-treated Syrian hamsters and decreased in Siberian hamsters, an effect partially reversed by coadministration of oPRL in Syrian, but not Siberian, hamsters. Thus, lowering serum PRL to short-day levels in long-day-housed hamsters of both species mimicked the directional change in body weight appropriate for each species when they are exposed to short days. This effect of CB-154 on body weight may be a result of some as yet unidentified effect of dopaminergic stimulation on overall growth since 1) these changes in body weight were not reflected as changes in lipid mass, as occurs naturally following short-day exposure for each species, and 2) neither species exhibited a reciprocal change in body weight when serum PRL was experimentally elevated in short days. Alternatively, it may be that once the energetic responses to short-day exposure have been fully expressed, the ability of PRL to stimulate the target sites of action for PRL for these responses may be decreased. BAT protein content, cytochrome oxidase activity (measures of metabolic growth of this tissue), and retroperitoneal total and specific lipoprotein lipase (LPL) activities were increased by CB-154 treatment in Syrian hamsters.(ABSTRACT TRUNCATED AT 400 WORDS)     

Are the actively respiring cells (CTC+) those responsible for bacterial production in aquatic environments?

The 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) staining method is commonly and increasingly used to detect and to enumerate actively respiring cells (CTC+ cells) in aquatic systems. However, this method remains controversial since some authors promote this technique while others pointed out several drawbacks of the method. Using flow cytometry (FCM), we showed that CTC staining kinetics vary greatly from one sample to another. Therefore, there is no universal staining protocol that can be applied to aquatic bacterial communities. Furthermore, using (3)H-leucine incorporation, it was shown that the CTC dye has a rapid toxic effect on bacterial cells by inhibiting protein synthesis, a key physiological function. The coupling of radioactive labelling with cell sorting by FCM suggested that CTC+ cells contribute to less than 60% of the whole bacterial activity determined at the community level. From these results, it is clearly demonstrated that the CTC method is not valid to detect active bacteria, i.e. cells responsible for bacterial production.     

Are rare variants responsible for susceptibility to complex diseases?

Little is known about the nature of genetic variation underlying complex diseases in humans. One popular view proposes that mapping efforts should focus on identification of susceptibility mutations that are relatively old and at high frequency. It is generally assumed-at least for modeling purposes-that selection against complex disease mutations is so weak that it can be ignored. In this article, I propose an explicit model for the evolution of complex disease loci, incorporating mutation, random genetic drift, and the possibility of purifying selection against susceptibility mutations. I show that, for the most plausible range of mutation rates, neutral susceptibility alleles are unlikely to be at intermediate frequencies and contribute little to the overall genetic variance for the disease. Instead, it seems likely that the bulk of genetic variance underlying diseases is due to loci where susceptibility mutations are mildly deleterious and where there is a high overall mutation rate to the susceptible class. At such loci, the total frequency of susceptibility mutations may be quite high, but there is likely to be extensive allelic heterogeneity at many of these loci. I discuss some practical implications of these results for gene mapping efforts.     

Demography of grey partridges Perdix perdix in Poland in the years 1991–2004: reasons of population decline

Grey partridge Perdix perdix populations were monitored in the years 1991–2004 in ten agricultural areas (100–200 km² each) located in various regions of Poland. Spring density (call counts in March/April) and parameters describing reproductive success (counts of adult and young birds in coveys found in August) were estimated, and annual survival rate of adult birds was calculated. In the 1990s, the mean spring density of grey partridge in Poland showed a threefold decrease. In 1993 (the year of the highest mean density), from 4.6 pairs/km² to 20.0 pairs/km² were found in individual areas; whereas in 2004, there were from 0.4 pairs/km² to 8.3 pairs/km². The mean brood-production rate in individual years ranged from 29% to 49% (overall mean 36.8%), the chick-survival rate from 31% to 56% (43.1%), the young production from 1.6 to 2.8 young per adult (2.32 young/adult) and the annual survival rate of adult birds from 25% to 33% (28.3%). The population decrease in the 1990s was connected with the drop of reproductive success, including both the brood-production rate and the chick-survival rate, as well as with the decline of annual survival rate of adult birds. The decrease of brood-production rate and adult-survival rate probably resulted mainly from increased abundance of nest and incubating female predators (particularly foxes). Fluctuations in chick-survival rate were related to weather conditions, but also slight long-term decline was recorded, probably due to more intensive pesticide use.     

Is pathological metabolism in the parental organism responsible for defective and monstrous development of the offspring?

Ohne Zusammenfassung

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Is pathological metabolism in the parental organism responsible for defective and monstrous development of the offspring?

     

Are the progestins responsible for breast cancer risk during hormone therapy in the postmenopause? Experimental vs. clinical data

Evidence is increasing suggesting that adding progestins to estrogen replacement therapy may be more harmful then beneficial, however it is debatable whether all progestins act equally on breast epithelial cells.

Experimental data with the comparison of various progestins in the same in vitro model present a rather high evidence that there may be differences between the various progestins regarding breast cancer risk. Especially of concern may be to differentiate between primary and secondary risk i.e. between benign and malignant breast epithelial cells.

The epidemiological studies and especially the Women's Health Initiative (WHI) trial, so far the only prospective placebo-controlled interventional study, demonstrate an increased risk under combined estrogen/progestin therapy, but they have the limitations that they up to now cannot discriminate between the various progestins mostly due to too small or not comparable patient numbers in the subgroups with the various progestins. However, there is evidence that the natural progesterone, possibly also the transdermal usage of synthetic progestins, may avoid an increased risk, but this must be proven in further clinical trials.