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  • 1
    In: Journal of Animal Ecology, May 2012, Vol.81(3), pp.516-523
    Description:  Model analyses show that the stability of population dynamics and food web persistence increase with the strength of interference competition. Despite this critical importance for community stability, little is known about how external factors such as the environmental temperature affect intraspecific interference competition.  We aimed to fill this void by studying the functional responses of two ground beetle species of different body size, and . These functional response experiments were replicated across four predator densities and two temperatures to address the impact of temperature on intraspecific interference competition.  We generally expected that warming should increase the speed of movement, encounter rates and in consequence interference among predator individuals. In our experiment, this expectation was supported by the results obtained for the larger predator, , whereas the opposite pattern characterized the interference behaviour of the smaller predator  These results suggest potentially nontrivial implications for the effects of environmental temperature on intraspecific interference competition, for which we propose an explanation based on the different sensitivity to warming of metabolic rates of both species. As expected, increasing temperature led to stronger interference competition of the larger species, , which exhibited a weaker increase in metabolic rate with increasing temperature. The stronger increase in the metabolic rate of the smaller predator, , had to be compensated by increasing searching activity for prey, which did not leave time for increasing interference.  Together, these results suggest that any generalization how interference competition responds to warming should also take the species’ metabolic response to temperature increases into account.
    Keywords: Food Webs ; Functional Responses ; Global Warming ; Interaction Strength ; Metabolic Rates
    ISSN: 0021-8790
    E-ISSN: 1365-2656
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  • 2
    Language: English
    In: The American Naturalist, 01 July 2017, Vol.190(1), pp.131-143
    Description: Living organisms are constrained by both resource quantity and quality. Ecological stoichiometry offers important insights into how the elemental composition of resources affects their consumers. If resource quality decreases, consumers can respond by shifting their body stoichiometry, avoiding low-quality resources, or up-regulating feeding rates to maintain the supply of required elements while excreting excess carbon (i.e., compensatory feeding). We analyzed multitrophic consumer body stoichiometry, biomass, and feeding rates along a resource-quality gradient in the litter of tropical forest and rubber and oil-palm plantations. Specifically, we calculated macroinvertebrate feeding rates based on consumer metabolic demand and assimilation efficiency. Using linear mixed effects models, we assessed resource-quality effects on macroinvertebrate detritivore and predator communities. We did not detect shifts in consumer body stoichiometry or decreases in consumer biomass in response to declining resource quality, as indicated by increasing carbon-to-nitrogen ratios. However, across trophic levels, we found a strong indication of decreasing resource quality leading to increased consumer feeding rates through altered assimilation efficiency and community body size structure. Our study reveals the influence of resource quality on multitrophic consumer feeding rates and suggests compensatory feeding to be more common across consumer trophic levels than was formerly known.
    Keywords: Resource Quality Depletion ; Ecological Stoichiometry ; Consumer Feeding Rates ; Consumer Resource Interaction ; Multitrophic Communities
    ISSN: 00030147
    E-ISSN: 15375323
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  • 3
    Language: English
    In: Sci Rep, 2018, Vol.8(1), pp.4399-4399
    Description: A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.
    Keywords: Biology;
    ISSN: 2045-2322
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  • 4
    Language: English
    In: Sci Rep, 2017, Vol.7(1), pp.8288-8288
    Description: Herbivory and disturbance are major drivers of biological invasions, but it is unclear how they interact to determine exotic vs. native seedling recruitment and what consequences arise for biodiversity and ecosystem functioning. Previous studies neglected the roles of different, potentially interacting, guilds of generalist herbivores such as rodents and gastropods. We therefore set up a full-factorial rodent exclusion x gastropod exclusion x disturbance x seed-addition experiment in a grassland community in Central Germany and measured early seedling recruitment, as well as species richness, species composition and aboveground biomass. Gastropod herbivory reduced the positive effect of disturbance on seedling recruitment, particularly for exotic species. Rodent herbivory had weak positive effects on seedling recruitment at undisturbed sites, irrespective of species origin. This effect was likely driven by their strong negative effect on productivity. Interactive effects between both herbivore guilds became only evident for species richness and composition. How many species established themselves depended on disturbance, but was independent of species origin. The fewer exotic species that established themselves increased productivity to a stronger extent compared to native species. Our study highlights that joint effects of disturbance, herbivory and species origin shape early recruitment, while they only weakly affect biodiversity and ecosystem functioning.
    Keywords: Article;
    ISSN: 2045-2322
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  • 5
    In: Microbiology, Nov, 1998, Vol.144(11), p.2979(7)
    Description: Research was conducted to examine the existence of a variant of the p50, an adhesin molecule, in Mycoplasma hominis. To investigate the ubiquity of P50 in M hominis and to determine if the isolates, which did not react with the mAb, contain and express the gene encoding P50, the isolates were studied at the mRNA and DNA level. Results indicated that p50 gene sequences were present in all M hominis isolates that were examined.
    Keywords: Mycoplasma -- Genetic Aspects ; Antigens -- Research ; Mutagenesis -- Research
    ISSN: 1350-0872
    E-ISSN: 14652080
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  • 6
    In: European Journal of Immunology, April 2012, Vol.42(4), pp.831-841
    Description: T‐cell activation and the subsequent transformation of activated cells into ‐cell blasts require profound changes in cell volume. However, the impact of cell volume regulation for ‐cell immunology has not been characterized. Here we studied the role of the cell‐volume regulating osmolyte transporter aut for ‐cell activation in aut‐deficient mice. T‐cell mediated recall responses were severely impaired in mice as shown with 16 melanoma rejection and hapten‐induced contact hypersensitivity. CD4 and CD8 cells were unequivocally located within peripheral lymph nodes of unprimed mice but significantly decreased in compared with mice following in vivo activation. Further analysis revealed that aut is critical for rescuing cells from activation‐induced cell death in vitro and in vivo as shown with , superantigen, and antigen‐specific activation. Consequently, reduction of CD4 and CD8 cells in mice upon antigen challenge resulted in impaired in vivo generation of ‐cell memory. These findings disclose for the first time that volume regulation in cells is an element in the regulation of adaptive immune responses and that the osmolyte transporter aut is crucial for ‐cell survival and ‐cell mediated immune reactions.
    Keywords: Activation‐Induced Cell Death ; Cell Volume Regulation ; Taurine Transporter ; T‐Cell Response
    ISSN: 0014-2980
    E-ISSN: 1521-4141
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  • 7
    Language: English
    In: Cell, 1997, Vol.91(5), pp.605-615
    Description: Invasion of human mucosal cells by N. gonorrhoeae via the binding to heparansulfate proteoglycan receptors is considered a crucial event of the infection. Using different human epithelial cells and primary fibroblasts, we show here an activation of the phosphatidylcholine-specific phospholipase C (PC-PLC) and acidic sphingomyelinase (ASM) by N. gonorrhoeae, resulting in the release of diacylglycerol and ceramide. Genetic and/or pharmacological blockade of ASM and PC-PLC cause inhibition of cellular invasion by N. gonorrhoeae. Complementation of ASM-deficient fibroblasts from Niemann-Pick disease patients restored N. gonorrhoeae-induced signaling and entry processes. The activation of PC-PLC and ASM, therefore, is an essential requirement for the entry of N. gonorrhoeae into distinct nonphagocytic human cell types including several epithelial cells and primary fibroblasts.
    Keywords: Biology
    ISSN: 0092-8674
    E-ISSN: 1097-4172
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  • 8
    Language: English
    In: Physiological genomics, 21 November 2011, Vol.43(22), pp.1255-62
    Description: Maternal lipoproteins have been studied extensively in human pregnancies, but little is known about the role of fetal lipoproteins. The vascularized human placenta interfaces between the mother and fetus to transfer nutrients for sustaining pregnancy. Unlike that of adults, fetal high-density lipoprotein (HDL), which is in contact with placental vessels, is characterized by a high proportion of apolipoprotein E (apoE). We hypothesize this unique composition of fetal HDL affects key functions of the growing fetal tissues. The aim was to identify genes regulated by apoE-HDL by incubating human placental endothelial cells (HPEC) with either fetal HDL or apoE-rich reconstituted HDL particles (apoE-rHDL). HPEC were exposed to 15 μg/ml fetal HDL, 15 μg/ml apoE-rHDL, or medium for 16 h, respectively. Microarray analysis determined genes regulated by fetal HDL and apoE. Characterization of HDL particles revealed a different hydrodynamic radius for apoE-rHDL (13.70 nm) compared with fetal HDL (18.11 nm). Stepwise gene clustering after microarray experiments identified 79 differentially expressed genes (P 〈 0.05) when cells were exposed to HDL compared with controls. Among them 16 genes were downregulated, whereas five genes were upregulated by twofold, respectively. When HPEC were incubated with apoE-rHDL 18-fold more genes (1,417, 12% of transcripts) were regulated (P 〈 0.05) in contrast to HDL. Thereof, 172 genes were downregulated and 376 genes upregulated (twofold). In the common subset of 38 genes regulated by both HDL particles, genes involved in cholesterol biosynthesis and cell protection prevailed. Strikingly, results suggest that HDL has the capability of regulating metallothioneins, which may have an effect on oxidative stress in HPEC.
    Keywords: Gene Expression Regulation ; Apolipoproteins E -- Genetics ; Endothelial Cells -- Metabolism ; Lipoproteins, HDL -- Genetics ; Placenta -- Metabolism
    ISSN: 10948341
    E-ISSN: 1531-2267
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  • 9
    Language: English
    In: Sci Rep, 2017, Vol.7(1), pp.12628-12628
    Description: Increased Lipoprotein associated phospholipase A (LpPLA) has been associated with inflammatory pathologies, including Type 2 Diabetes. Studies on LpPLA and Gestational Diabetes Mellitus (GDM) are rare, and have focused mostly on maternal outcome. In the present study, we investigated whether LpPLA activity on foetal lipoproteins is altered by maternal GDM and/or obesity (a major risk factor for GDM), thereby contributing to changes in lipoprotein functionality. We identified HDL as the major carrier of LpPLA activity in the foetus, which is in contrast to adults. We observed marked expression of LpPLA in placental macrophages (Hofbauer cells; HBCs) and found that LpPLA activity in these cells was increased by insulin, leptin, and pro-inflammatory cytokines. These regulators were also increased in plasma of children born from GDM pregnancies. Our results suggest that insulin, leptin, and pro-inflammatory cytokines are positive regulators of LpPLA activity in the foeto-placental unit. Of particular interest, functional assays using a specific LpPLA inhibitor suggest that high-density lipoprotein (HDL)-associated LpPLA exerts anti-oxidative, athero-protective functions on placental endothelium and foetus. Our results therefore raise the possibility that foetal HDL-associated LpPLA might act as an anti-inflammatory enzyme improving vascular barrier function.
    Keywords: Biology;
    ISSN: 2045-2322
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  • 10
    Language: English
    In: Cellular Physiology and Biochemistry, June 2012, Vol.29(5-6), pp.809-818
    Description: Background: Cardiac action potential repolarisation is determined by K+ currents including IKs. IKs channels are heteromeric channels composed of KCNQ1 and KCNE E-subunits. Mutations in KCNQ1 are associated with sinus bradycardia, familial atrial fibrillation (fAF) and/or short QT syndrome as a result of gain-of-function, and long QT syndrome (LQTS) due to loss-of-function in the ventricles. Here, we report that the missense mutation R231C located in S4 voltage sensor domain is associated with a combined clinical phenotype of sinus bradycardia, fAF and LQTS. We aim to understand the molecular basis of the complex clinical phenotype. Methods: We expressed and functionally analyzed the respective channels kinetics in Xenopus laevis oocytes. The molecular nature of the residue R231 was studied by homology modeling and molecular dynamics simulation. Results: As a result, the mutation reduced voltage sensitivity of channels, possibly due to neutralization of the positive charge of the arginine side chain substituted by cysteine. Modeling suggested that the charge carrying side chain of R231 is positioned suitably to transfer transmembrane voltages into conformational energy. Further, the mutation altered the functional interactions with KCNE subunits. Conclusion: The mutation acted in a E-subunit dependent manner, suggesting IKs function altered by the presence of different KCNE subunits in sinus node, atria and ventricles as the molecular basis of sinus bradycardia, fAF and LQTS in mutation carriers.
    Keywords: Original Paper ; Kcne ; Heart ; Arrhythmia ; Oocyte ; Kv7.1 ; Kvlqt1 ; Biology ; Chemistry
    ISSN: 1015-8987
    E-ISSN: 1421-9778
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