990 resultados para TROPHIC RELATIONSHIPS
Resumo:
The gain coefficient of the strongest 3p --> 3s, J = 2 --> 1 lasing transition at 23.6 nm in the Ne-like Ge collisional excitation scheme has been measured, using the fundamental wavelength from a Nd:glass laser (1.06-mu-m), for a range of incident intensities on massive stripe targets up to 2.2 cm in length. From a threshold incident laser intensity of approximately 6 x 10(12) W/cm2, the gain coefficient rises to approximately 4.5 cm-1 for an irradiation intensity of approximately 2.5 x 10(13) W/cm2, tending towards still higher gain coefficients at higher incident intensities. For targets of maximum length, a gain-length product gL almost-equal-to 10 was reached with a resultant output power at 23.6 nm estimated to be at the approximately kW level. The beam divergence decreased with length to a minimum of approximately 7 mrad but no significant trend in beam pointing with plasma length was observed. From the trend in the gain coefficient, it appears that for a fixed energy laser irradiating a approximately 100-mu-m wide slab targets, an incident intensity of I(i) approximately 1.2 x 10(13) W/cm2 represents an optimum working level, assuming that plasma length is not limited by refractive effects. In addition to the usual valence electron excited 3p --> 3s transitions, the gain coefficient for the core excited 1s(2)2s2p(6)3d --> 1s(2)2s2p(6)3p transition at 19.9 nm has been measured to be approximately 1.5 cm-1 for an incident irradiance of approximately 2.5 x 10(13) W/cm2.
Resumo:
The current morphological classification of the Demospongiae G4 clade was tested using large subunit ribosomal RNA (LSU rRNA) sequences from 119 taxa. Fifty-three mitochondrial cytochrome oxidase 1 (CO1) barcoding sequences were also analysed to test whether the 28S phylogeny could be recovered using an independent gene. This is the largest and most comprehensive study of the Demospongiae G4 clade. The 28S and CO1 genetrees result in congruent clades but conflict with the current morphological classification. The results confirm the polyphyly of Halichondrida, Hadromerida, Dictyonellidae, Axinellidae and Poecilosclerida and show that several of the characters used in morphological classifications are homoplasious. Robust clades are clearly shown and a new hypothesis for relationships of taxa allocated to G4 is proposed. (C) 2011 Elsevier Inc. All rights reserved.
Resumo:
This study reports the potent myoactivity of flatworm FMRFamide-related peptides (FaRPs) on isolated muscle fibers of the human blood fluke, Schistosoma mansoni. The turbellarian peptides YIRFamide (EC50 4 eta M), GYIRFamide (EC50 1 eta M). and RYIRFamide (EC50 7 eta M), all induced muscle contraction more potently than the cestode FaRP GNFFRFamide (EC50 500 eta M). Using a series of synthetic analogs of the flatworm peptides YIRFamide, GYIRFamide and RYIRFamide, the structure-activity relationships of the muscle FaRP receptor were examined. With a few exceptions, each residue in YIRFamide is important in the maintenance of its myoactivity. Alanine scans resulted in peptides that were inactive (Ala(1), Ala(2), Ala(3) and Ala(4) YIRFamide; Ala(4) and Ala(5) RYIRFamide) or had much reduced potencies (Ala(1), Ala(2) and Ala(3) RYIRFamide). Substitution of the N-terminal (Tyr(1)) residue of YIRFamide with the non-aromatic residues Thr or Arg produced analogs with greatly reduced potency. Replacement of the N-terminal Tyr with aromatic amino acids resulted in myoactive peptides (FIRFamide, EC50 100 eta M; WIRFamide, EC50 0.5 eta M). The activity of YIRFamide analogs which possessed a Leu(2), Phe(2) or Met(2) residue (EC50's 10, 1 and 3 eta M, respectively) instead of Ile(2) was not significantly altered, whereas, YVRFamide had a greatly reduced (EC50 200 eta M) activity. Replacement of the Phe(4) with a Tyr(4) (YIRYamide) also greatly lowered potency. Truncated analogs were either inactive (FRFamide, YRFamide, HRFamide, RFamide, Famide) or had very low potency (IRFamide and MRFamide), with the exception of nLRFamide (EC50 20 eta M). YIRF free acid was inactive. In summary, these data show the general structural requirements of this schistosome muscle FaRP receptor to be similar, but not identical, to those of previously characterized molluscan FaRP receptors. (C) 1997 Elsevier Science Inc.
Resumo:
Marine ecosystems and their associated populations are increasingly at risk from the cumulative impacts of many anthropogenic threats that increase the likelihood of species extinction and altered community dynamics. In response, marine reserves can be used to protect exploited species and conserve biodiversity. The increased abundance of predatory species in marine reserves may cause indirect effects along chains of multi-trophic interactions. These trophic cascades can arise through direct predation, density-mediated indirect interactions (DMIIs), or indirect behavioural effects, termed trait-mediated indirect interactions (TMIIs). The extent of algal cover and the abundance of 4 primary consumers were determined in Lough Hyne, which was designated Europe's first marine nature reserve in 1981. The primary consumers were the sea urchin Paracentrotus lividus, the topshell Gibbula cineraria, the oyster Anomia ephippium, and the scallop Chlamys varia. The abundances of 3 starfish species (Marthasterias glacialis, Asterias rubens, and Asterina gibbosa) were also determined, as were 2 potential crustacean predators, Necora puber and Carcinus maenas. These data were compared with historical data from a 1962 (prey) and a 1963 (predator) survey to determine the nature of community interactions over adjacent trophic levels. The present study reveals a breakdown in population structure of the 4 surveyed prey species. Marine reserve designation has led to an increase in predatory crabs and M. glacialis, a subsequent decrease in primary consumers, especially the herbivore P. lividus, and an increase in macroalgal cover which is indicative of a trophic cascade. The study shows that establishing a Marine Reserve does not guarantee that conservation benefits will be distributed equally.
Resumo:
Recent research has generally shown that a small change in the number of species in a food web can have consequences both for community structure and ecosystem processes. However 'change' is not limited to just the number of species in a community, but might include an alteration to such properties as precipitation, nutrient cycling and temperature, all of which are correlated with productivity. Here we argue that predicted scenarios of global change will result in increased plant productivity. We model three scenarios of change using simple Lotka-Volterra dynamics, which explore how a global change in productivity might affect the strength of local species interactions and detail the consequences for community and ecosystem level stability. Our results indicate that (i) at local scales the average population size of consumers may decline because of poor quality food resources, (ii) that the strength of species interactions at equilibrium may become weaker because of reduced population size, and (iii) that species populations may become more variable and may take longer to recover from environmental or anthropogenic disturbances. At local scales interaction strengths encompass such properties as feeding rates and assimilation efficiencies, and encapsulate functionatty important information with regard to ecosystem processes. Interaction strengths represent the pathways and transfer of energy through an ecosystem. We examine how such local patterns might be affected given various scenarios of 'global change' and discuss the consequences for community stability and ecosystem functioning. (C) 2004 Elsevier GmbH. All rights reserved.
Resumo:
Signal Transducers and Activators of Transcription (STAT) proteins are a group of latent cytoplasmic transcription factors involved in cytokine signaling. STAT3 is a member of the STAT family and is expressed at elevated levels in a large number of diverse human cancers and is now a validated target for anticancer drug discovery.. Understanding the dynamics of the STAT3 dimer interface, accounting for both protein-DNA and protein-protein interactions, with respect to the dynamics of the latent unphosphorylated STAT3 monomer, is important for designing potential small-molecule inhibitors of the activated dimer. Molecular dynamics (MD) simulations have been used to study the activated STAT3 homodimer:DNA complex and the latent unphosphorylated STAT3 monomer in an explicit water environment. Analysis of the data obtained from MD simulations over a 50 ns time frame has suggested how the transcription factor interacts with DNA, the nature of the conformational changes, and ways in which function may be affected. Examination of the dimer interface, focusing on the protein-DNA interactions, including involvement of water molecules, has revealed the key residues contributing to the recognition events involved in STAT3 protein-DNA interactions. This has shown that the majority of mutations in the DNA-binding domain are found at the protein-DNA interface. These mutations have been mapped in detail and related to specific protein-DNA contacts. Their structural stability is described, together with an analysis of the model as a starting-point for the discovery of novel small-molecule STAT3 inhibitors.