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Dramatic Variation (dramatic + variation)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

The structure of bacterial communities in the western Arctic Ocean as revealed by pyrosequencing of 16S rRNA genes

ENVIRONMENTAL MICROBIOLOGY, Issue 5 2010
David L. Kirchman
Summary Bacterial communities in the surface layer of the oceans consist of a few abundant phylotypes and many rare ones, most with unknown ecological functions and unclear roles in biogeochemical processes. To test hypotheses about relationships between abundant and rare phylotypes, we examined bacterial communities in the western Arctic Ocean using pyrosequence data of the V6 region of the 16S rRNA gene. Samples were collected from various locations in the Chukchi Sea, the Beaufort Sea and Franklin Bay in summer and winter. We found that bacterial communities differed between summer and winter at a few locations, but overall there was no significant difference between the two seasons in spite of large differences in biogeochemical properties. The sequence data suggested that abundant phylotypes remained abundant while rare phylotypes remained rare between the two seasons and among the Arctic regions examined here, arguing against the ,seed bank' hypothesis. Phylotype richness was calculated for various bacterial groups defined by sequence similarity or by phylogeny (phyla and proteobacterial classes). Abundant bacterial groups had higher within-group diversity than rare groups, suggesting that the ecological success of a bacterial lineage depends on diversity rather than on the dominance of a few phylotypes. In these Arctic waters, in spite of dramatic variation in several biogeochemical properties, bacterial community structure was remarkably stable over time and among regions, and any variation was due to the abundant phylotypes rather than rare ones. [source]

Cultural Variations in the Placebo Effect: Ulcers, Anxiety, and Blood Pressure

MEDICAL ANTHROPOLOGY QUARTERLY, Issue 1 2000
Daniel E. Moerman
An analysis of the control groups in double-blind trials of medicines demonstrates broad variation,from 0 to 100 percent,in placebo effectiveness rates for the same treatment for the same condition. In two cases considered here, drug healing rates covary with placebo healing rates; placebo healing is the ultimate and inescapable "complementary medicine. " Several factors can account for the dramatic variation in placebo healing rates, including cultural ones. But because variation differs by illness, large placebo effects for one condition do not necessarily anticipate large placebo effects for other conditions as well. Deeper understanding of the intimate relationship between cultural and biological processes will require close ethnographic scrutiny of the meaningfulness of medical treatment in different societies, [placebo effect, ulcer disease, anxiety, hypertension, cross-cultural variation] [source]

Genetic divergence does not predict change in ornament expression among populations of stalk-eyed flies

MOLECULAR ECOLOGY, Issue 12 2005
JOHN G. SWALLOW
Abstract Stalk-eyed flies (Diptera: Diopsidae) possess eyes at the ends of elongated peduncles, and exhibit dramatic variation in eye span, relative to body length, among species. In some sexually dimorphic species, evidence indicates that eye span is under both intra- and intersexual selection. Theory predicts that isolated populations should evolve differences in sexually selected traits due to drift. To determine if eye span changes as a function of divergence time, 1370 flies from 10 populations of the sexually dimorphic species, Cyrtodiopsis dalmanni and Cyrtodiopsis whitei, and one population of the sexually monomorphic congener, Cyrtodiopsis quinqueguttata, were collected from Southeast Asia and measured. Genetic differentiation was used to assess divergence time by comparing mitochondrial (cytochrome oxidase II and 16S ribosomal RNA gene fragments) and nuclear (wingless gene fragment) DNA sequences for c. five individuals per population. Phylogenetic analyses indicate that most populations cluster as monophyletic units with up to 9% nucleotide substitutions between populations within a species. Analyses of molecular variance suggest a high degree of genetic structure within and among the populations; > 97% of the genetic variance occurs between populations and species while < 3% is distributed within populations, indicating that most populations have been isolated for thousands of years. Nevertheless, significant change in the allometric slope of male eye span on body length was detected for only one population of either dimorphic species. These results are not consistent with genetic drift. Rather, relative eye span appears to be under net stabilizing selection in most populations of stalk-eyed flies. Given that one population exhibited dramatic evolutionary change, selection, rather than genetic variation, appears to constrain eye span evolution. [source]

Strength of C,H Bonds at Nitrogen , -Position:Implication for Metabolic Stability of Nitrogen-containing Drug Molecules

CHINESE JOURNAL OF CHEMISTRY, Issue 4 2008
Xiang-Ming MENG
Abstract The available experimental ,C-H BDEs of a variety of amine-containing molecules were examined by using the G3B3 and CBS-Q methods. The verified values were employed to benchmark and calibrate the density functional theory methods. It was found that the (U)BHandH/6-311++G(2df, 2p)//(U)B3LYP/6-31G(d) method was a fast and accurate method for calculating C,H BDEs at nitrogen , -positions. By using the newly benchmarked BHandH method, the ,C,H BDEs in a number of nitrogen-containing drug molecules were calculated, where a dramatic variation of the ,C,H BDEs was discovered. To understand this variation, the effects of mono- and double-substitution at both carbon and nitrogen atoms on the ,C-H BDEs were systematically studied. The origin of the substitution effects was thoroughly discussed in terms of four categories of substituents. [source]