790 research outputs found
Rapid bioconcentration of steroids in the plasma of three-spined stickleback Gasterosteus aculeatus exposed to waterborne testosterone and 17β-oestradiol
The relationship over time between the concentrations of two steroids, singly and in combination, in a static exposure system and in the blood of three-spined stickleback Gasterosteus aculeatus, held within the exposure system was investigated. Groups of three-spined stickleback were exposed (nominally) to either 1000 ng l1 17β-oestradiol (E2), testosterone (T) or E2 and T in combination at the same concentrations for 6 days. Both water and fish were sampled at intervals and steroid concentrations in both compartments were determined. The plasma steroid time profile revealed a rapid bioconcentration within the first 6 h of exposure. The plasma steroid levels attained at this time point (20–90 ng ml1) were up to 50-fold (E2) and 200-fold (T) greater than the actual levels of steroid measured in the exposure water, while levels in the blood of control fish did not exceed 4 ng ml1. The substantial elevation of plasma steroid levels relative to the concentrations of steroid to which the fish were exposed in the ambient water gives scope for delivery of the steroids to target endocrine tissues at levels far in excess of what might be predicted on the basis of passive branchial uptake alone. These results are discussed in relation to endocrine disruption, and in particular the occurrence of effects in fish exposed to levels of endocrine active substances that are seemingly physiologically irrelevant
Convective Fingering of an Autocatalytic Reaction Front
We report experimental observations of the convection-driven fingering
instability of an iodate-arsenous acid chemical reaction front. The front
propagated upward in a vertical slab; the thickness of the slab was varied to
control the degree of instability. We observed the onset and subsequent
nonlinear evolution of the fingers, which were made visible by a {\it p}H
indicator. We measured the spacing of the fingers during their initial stages
and compared this to the wavelength of the fastest growing linear mode
predicted by the stability analysis of Huang {\it et. al.} [{\it Phys. Rev. E},
{\bf 48}, 4378 (1993), and unpublished]. We find agreement with the thickness
dependence predicted by the theory.Comment: 11 pages, RevTex with 3 eps figures. To be published in Phys Rev E,
[email protected], [email protected], [email protected]
Diversity and community biomass depend on dispersal and disturbance in microalgal communities
The evidence for species diversity effects
on ecosystem functions is mainly based on studies not
explicitly addressing local or regional processes
regulating coexistence or the importance of community
structure in terms of species evenness. In experimental
communities of marine benthic microalgae,
we altered the successional stages and thus the strength
of local species interactions by manipulating rates of
dispersal and disturbance. The treatments altered
realized species richness, evenness and community
biomass. For species richness, dispersal mattered only
at high disturbance rates; when opening new space,
dispersal led to maximized richness at intermediate
dispersal rates. Evenness, in contrast, decreased with
dispersal at low or no disturbance, i.e. at late successional stages. Community biomass showed a nonlinear
hump-shaped response to increasing dispersal at
all disturbance levels.We found a positive correlation
between richness and biomass at early succession, and
a strong negative correlation between evenness and
biomass at late succession. In early succession both
community biomass and richness depend directly on
dispersal from the regional pool, whereas the late
successional pattern shows that if interactions allow
the most productive species to become dominant,
diverting resources from this species (i.e. higher
evenness) reduces production. Our study emphasizes
the difference in biodiversity–function relationships
over time, as different mechanisms contribute to the
regulation of richness and evenness in early and late
successional stages
Preoperative systemic inflammation predicts postoperative infectious complications in patients undergoing curative resection for colorectal cancer
The presence of systemic inflammation before surgery, as evidenced by the glasgow prognostic score (mGPS), predicts poor long-term survival in colorectal cancer. The aim was to examine the relationship between the preoperative mGPS and the development of postoperative complications in patients undergoing potentially curative resection for colorectal cancer. Patients (n=455) who underwent potentially curative resections between 2003 and 2007 were assessed consecutively, and details were recorded in a database. The majority of patients presented for elective surgery (85%) were over the age of 65 years (70%), were male (58%), were deprived (53%), and had TNM stage I/II disease (61%), had preoperative haemoglobin (56%), white cell count (87%) and mGPS 0 (58%) in the normal range. After surgery, 86 (19%) patients developed a postoperative complication; 70 (81%) of which were infectious complications. On multivariate analysis, peritoneal soiling (P<0.01), elevated preoperative white cell count (P<0.05) and mGPS (P<0.01) were independently associated with increased risk of developing a postoperative infection. In elective patients, only the mGPS (OR=1.75, 95% CI=1.17-2.63, P=0.007) was significantly associated with increased risk of developing a postoperative infection. Preoperative elevated mGPS predicts increased postoperative infectious complications in patients undergoing potentially curative resection for colorectal cancer
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