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1.
Alf?NorkkoEmail author Simon?F.?Thrush Vonda?J.?Cummings Greig?A.?Funnell Anne-Maree?Schwarz Neil?L.?Andrew Ian?Hawes 《Polar Biology》2004,27(8):482-494
At Cape Evans on Ross Island, Antarctica, the rhodophyte Phyllophora antarctica is the dominant primary producer in terms of biomass from 10 to >30 m depth. The vast majority of Phyllophora occurs as accumulations of unattached plants. Whilst decomposition and incorporation of macroalgal drift material into the food web is rapid in temperate ecosystems, we predicted these processes to be slow in Antarctica. We address the functional role of macroalgal detritus in fuelling the biodiversity of benthic communities at Cape Evans during the summers of 2001 and 2002. Specifically we (a) describe the distribution and biomass of attached and drift algae, (b) assess the photosynthetic capacity and degradation of drift accumulations using in situ fluorometry, (c) assess the effect of patches of drift Phyllophora on underlying macrofaunal communities, and, (d) use stable isotopes to investigate the possible uptake of Phyllophora by macrofauna. We found drift Phyllophora accumulations throughout the depth range investigated (3–31 m), with peak biomasses of 140±30 g dwt m–2 in the 15–25 m depth strata. At this depth stratum Phyllophora was a conspicuous habitat element with the % cover on the seafloor averaging 30%. While initially the drift algal accumulations appeared in good health we measured significant declines in photosynthetic capacity between years suggesting ongoing, albeit slow, degradation of the drift algal accumulations. Our results demonstrate that Phyllophora drift accumulations have a structuring role on soft-sediment communities, which increases in strength with the gradual degradation of the algae. The longevity of Phyllophora is enhanced by secondary metabolites, which serve as protection against grazers, and their extreme shade adaptation. However, our carbon and nitrogen stable isotope data of polychaetes and amphipods associated with Phyllophora suggest that macroalgal detritus enters the food web, and although this process is slow, Phyllophora accumulations might serve to dampen the seasonality in food supply providing higher trophic levels with a more constant food source. 相似文献
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Blake C. Ballif Aaron Theisen Ryan N. Traylor Devon Lamb Thrush Caroline Astbury Dennis Bartholomew Kim L. McBride Robert E. Pyatt Kate Shane Wendy E. Smith William B. Gallentine M. Katharine Rudd Julia A. Keene Jean P. Pfotenhauer Pawel Stankiewicz Bassem A. Bejjani 《American journal of human genetics》2010,86(3):454-461
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Holloway GP Thrush AB Heigenhauser GJ Tandon NN Dyck DJ Bonen A Spriet LL 《American journal of physiology. Endocrinology and metabolism》2007,292(6):E1782-E1789
A reduction in fatty acid oxidation has been associated with lipid accumulation and insulin resistance in the skeletal muscle of obese individuals. We examined whether this decrease in fatty acid oxidation was attributable to a reduction in muscle mitochondrial content and/or a dysfunction in fatty acid oxidation within mitochondria obtained from skeletal muscle of age-matched, lean [body mass index (BMI) = 23.3 +/- 0.7 kg/m2] and obese women (BMI = 37.6 +/- 2.2 kg/m2). The mitochondrial marker enzymes citrate synthase (-34%), beta-hydroxyacyl-CoA dehydrogenase (-17%), and cytochrome c oxidase (-32%) were reduced (P < 0.05) in obese participants, indicating that mitochondrial content was diminished. Obesity did not alter the ability of isolated mitochondria to oxidize palmitate; however, fatty acid oxidation was reduced at the whole muscle level by 28% (P < 0.05) in the obese. Mitochondrial fatty acid translocase (FAT/CD36) did not differ in lean and obese individuals, but mitochondrial FAT/CD36 was correlated with mitochondrial fatty acid oxidation (r = 0.67, P < 0.05). We conclude that the reduction in fatty acid oxidation in obese individuals is attributable to a decrease in mitochondrial content, not to an intrinsic defect in the mitochondria obtained from skeletal muscle of obese individuals. In addition, it appears that mitochondrial FAT/CD36 may be involved in regulating fatty acid oxidation in human skeletal muscle. 相似文献
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Background
Whether inhaled corticosteroids suppress airway inflammation in chronic obstructive pulmonary disease (COPD) remains controversial. We sought to determine the effects of inhaled corticosteroids on sputum indices of inflammation in stable COPD.Methods
We searched MEDLINE, EMBASE, CINAHL, and the Cochrane Databases for randomized, controlled clinical trials that used induced sputum to evaluate the effect of inhaled corticosteroids in stable COPD. For each chosen study, we calculated the mean differences in the concentrations of sputum cells before and after treatment in both intervention and control groups. These values were then converted into standardized mean differences to accommodate the differences in patient selection, clinical treatment, and biochemical procedures that were employed across original studies. If significant heterogeneity was present (p < 0.10), then a random effects model was used to pool the original data. In the absence of significant heterogeneity, a fixed effects model was used.Results
We identified six original studies that met the inclusion criteria (N = 162 participants). In studies with higher cumulative dose (≥ 60 mg) or longer duration of therapy (≥ 6 weeks), inhaled corticosteroids were uniformly effective in reducing the total cell, neutrophil, and lymphocyte counts. In contrast, studies with lower cumulative dose (< 60 mg) or shorter duration of therapy (< 6 weeks) did not demonstrate a favorable effect of inhaled corticosteroids on these sputum indices.Conclusions
Our study suggests that prolonged therapy with inhaled corticosteroids is effective in reducing airway inflammation in stable COPD. 相似文献6.
Sharkey KJ Fernandez C Morgan KL Peeler E Thrush M Turnbull JF Bowers RG 《Journal of mathematical biology》2006,53(1):61-85
The process of infection during an epidemic can be envisaged as being transmitted via a network of routes represented by a
contact network. Most differential equation models of epidemics are mean-field models. These contain none of the underlying
spatial structure of the contact network. By extending the mean-field models to pair-level, some of the spatial structure
can be contained in the model. Some networks of transmission such as river or transportation networks are clearly asymmetric,
whereas others such as airborne infection can be regarded as symmetric. Pair-level models have been developed to describe
symmetric contact networks. Here we report on work to develop a pair-level model that is also applicable to asymmetric contact
networks. The procedure for closing the model at the level of pairs is discussed in detail. The model is compared against
stochastic simulations of epidemics on asymmetric contact networks and against the predictions of the symmetric model on the
same networks.
DEFRA funded project FC1153 相似文献
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The input of terrestrial silt and clay (hereafter mud) into coastal environments can alter sediment grain size distribution affecting the structure and functioning of benthic communities. The relationship between sediment mud content and macrofaunal community structure has been well documented, but not the effects on ecosystem function. In 143 plots from the mid-intertidal sites in 9 estuaries, we measured sediment properties, macrofaunal community composition and fluxes of O2 and NH4 + across the sediment–water interface to derive process-based measures of ecosystem function across the sand–mud gradient. We observed reductions in measures of macrofaunal diversity and decreases in the maximum density of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH4 + efflux (NH4 +) and biomass standardized gross primary production (GPPChl-a ) also decreased with increasing mud content. Environmental predictors explained 34–39% (P = 0.005–0.01) of the total variation in ecosystem function in distance-based linear models. After partitioning out the effect of mud, A. stutchburyi abundance was positively correlated and explained 25 and 23% (P = 0.0001) of the variation of SOC and NH4 +, respectively. Also, mud content (negatively correlated) and temperature (positively correlated) explained 26% of variability in GPPChl-a (P = 0.0001). Our results highlight the importance of increased mud content and the associated reduction in the abundance of strongly interacting key species on the loss of ecosystem function in intertidal sand flats. 相似文献
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Significance of nucleotide sequence alignments: a method for random sequence permutation that preserves dinucleotide and codon usage 总被引:10,自引:0,他引:10
The similarity of two nucleotide sequences is often expressed in terms of
evolutionary distance, a measure of the amount of change needed to
transform one sequence into the other. Given two sequences with a small
distance between them, can their similarity be explained by their base
composition alone? The nucleotide order of these sequences contributes to
their similarity if the distance is much smaller than their average
permutation distance, which is obtained by calculating the distances for
many random permutations of these sequences. To determine whether their
similarity can be explained by their dinucleotide and codon usage, random
sequences must be chosen from the set of permuted sequences that preserve
dinucleotide and codon usage. The problem of choosing random dinucleotide
and codon-preserving permutations can be expressed in the language of graph
theory as the problem of generating random Eulerian walks on a directed
multigraph. An efficient algorithm for generating such walks is described.
This algorithm can be used to choose random sequence permutations that
preserve (1) dinucleotide usage, (2) dinucleotide and trinucleotide usage,
or (3) dinucleotide and codon usage. For example, the similarity of two
60-nucleotide DNA segments from the human beta-1 interferon gene
(nucleotides 196-255 and 499-558) is not just the result of their nonrandom
dinucleotide and codon usage.
相似文献
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